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Airborne imagery of a disintegrating Sargassum drift line
Abstract
Airborne hyperspectral and thermal infrared imagery collected over the Florida Current provide a view of the disintegration of a Sargassum drift line in 5 m s−1 winds. The drift line consists mostly of rafts 20–80 m2 in size, though aggregations larger than 1000 m2 also occur. Rafts tend to be elongated, curved in the upwind direction, and 0.1–0.5 °C warmer than the surrounding ocean surface. Long weed ‘trails’ extending upwind from the rafts are evidence of plants dropping out and being left behind more rapidly drifting rafts. The raft line may be a remnant of an earlier Sargassum frontal band, which is detectible as an upwind thermal front and areas of submerged weed. Issues are identified that require future field measurements.Research highlights► A Sargassum drift line disintegrates under a wind speed of 5 m s−1. ► Weed left behind more rapidly drifting rafts form long upwind ‘trails’. ► Wave drag may be creating a distinct raft-and-trail morphology. ► Remnant frontal accumulations of only submerged Sargassum occur upwind.
... Where structure is otherwise limited, Sargassum aggregations offer refuge from predation, shelter from water movement, and productive foraging and nursery habitat 4,5,[19][20][21] . Sargassum aggregations may also provide warmer environments for associated fauna by absorbing solar energy and reducing water movement and heat dispersal 22,23 , thereby increasing water temperature relative to open water. ...
... We expect that holopelagic Sargassum may serve a similar function for associated fauna. Airborne thermal infrared imagery 22 and ex situ temperature measurements of seawater with and without Sargassum 23 support the prediction that Sargassum aggregations are warmer than open water. However, thermal profiles of Sargassum aggregations have not been evaluated in situ, and knowledge of thermal characteristics of Sargassum aggregations is otherwise limited. ...
... Sampling was conducted during daylight hours when the solar disk was not obstructed by clouds and in sea states of Beaufort Force ≤ 3. Sampling was restricted to these conditions to minimize variation in incoming solar radiation and water movement and control for temporal variation in environmental conditions that affect seawater temperature 32 and Sargassum aggregation state 33 . Drifting Sargassum occurs as dispersed fragments and individual thalli or "clumps" 17,21,33,34 typically 0.1-0.5 m across 3 ; lines or "windrows" of Sargassum aggregated parallel with the wind direction and stabilized by Langmuir circulation 2,3 varying in width from < 0.5 m to several m 22,33,34 ; and "mats" or "rafts" of aggregated Sargassum several m in extent up to tens or hundreds of m across 3,17,22,33,34 , which may be associated with windrows 33,34 or occur as discrete aggregations more likely to form in calm conditions 2,3 . Sargassum distribution in the Sargasso Sea is irregular and patchy 3 , large aggregations are uncommon, and clumps and windrows are most frequently observed in groups of 1-5 33 . ...
Drifting aggregations of Sargassum algae provide critical habitat for endemic, endangered, and commercially important species. They may also provide favorable microclimates for associated fauna. To quantify thermal characteristics of holopelagic Sargassum aggregations, we evaluated thermal profiles of 50 aggregations in situ in the Sargasso Sea. Sea surface temperature (SST) in the center of aggregations was significantly higher than in nearby open water, and SST differential was independent of aggregation volume, area, and thickness. SST differential between aggregation edge and open water was smaller than those between aggregation center and aggregation edge and between aggregation center and open water. Water temperature was significantly higher inside and below aggregations compared to open water but did not vary inside aggregations with depth. Holopelagic Sargassum aggregations provide warmer microhabitats for associated fauna, which may benefit marine ectotherms, though temperature differentials were narrow (up to 0.7 °C) over the range of aggregation sizes we encountered (area 0.01–15 m2). We propose a hypothetical curve describing variation in SST differential with Sargassum aggregation size as a prediction for future studies to evaluate across temporal and geographic ranges. Our study provides a foundation for investigating the importance of thermal microhabitats in holopelagic Sargassum ecosystems.
... Holopelagic Sargassum may be observed in multiple states (Fig. 1;Parr, 1939;Butler et al., 1983;Marmorino et al., 2011;Ody et al., 2019). Fragments are short fronds less than 20 cm in length, broken off a clump. ...
... Windrows are defined as aggregations of many fragments and/or clumps in a line generally arranged parallel to the wind direction (Figs. 1B and 1C); they may extend for multiple km distance and range in width from <0.5 m to several m (Woodcock, 1950;Marmorino et al., 2011). Mats are densely-packed holopelagic Sargassum fragments and/or clumps with a clear edge, irregular to round shape, and 5 to 100s m distance across. ...
... Often mats are observed associated with a windrow, exhibiting noticeably greater diameter/width (4-5 times) compared to the average of the windrow itself (Figs. 1D and 1E;Marmorino et al., 2011;Ody et al., 2019); under calm conditions, mats may be observed as completely independent features not connected to a windrow (Parr, 1939). The processes controlling formation and dissipation of holopelagic Sargassum windrows and mats as well as the timescale of transitions between local aggregation states remain poorly understood. ...
Between 2011 and 2020, 6,790 visual observations of holopelagic Sargassum were recorded across the North Atlantic Ocean to describe regional distribution, presence, and aggregation state at hourly and 10 km scales. Influences of oceanographic region and wind/sea conditions as well as temporal trends were considered; marine megafauna associates documented the ecological value of aggregations. Holopelagic Sargassum was present in 64% of observations from the western North Atlantic. Dispersed holopelagic Sargassum fragments and clumps were found in 97% of positive observations whereas aggregated windrows (37%) and mats (1%) were less common. Most field observations noted holopelagic Sargassum in quantities below the AFAI algorithm detection limit for the MODIS sensor. Aggregation state patterns were similar across regions; windrow proportion increased with higher wind speeds. In 8 of 10 years in the Sargasso Sea holopelagic Sargassum was found in over 65% of observations. In contrast, the Tropical Atlantic and Caribbean Sea exhibited greater inter-annual variability (1–88% and 11–78% presence, respectively) that did not align with extremes in central Atlantic holopelagic Sargassum areal coverage determined from satellite observations. Megafauna association patterns varied by taxonomic group. While some study regions were impacted by holopelagic Sargassum dynamics in the equatorial Atlantic, the Sargasso Sea had consistently high presence and operated independently. Field observations capture important dynamics occurring at fine spatiotemporal scales, including transient aggregation processes and ecological value for megafauna associates, and therefore remain essential to future studies of holopelagic Sargassum .
... There has been constant progress in the development of remote sensing for floating marine vegetation such as Sargassum species, in order to provide accurate information on their distribution and to quantify their coverage area and biomass (e.g. [21,29,30,[38][39][40][41][42][43][44][45][46][47][48]). The occurrence of large pelagic Sargassum aggregations in the Tropical North Atlantic was first detected from space in 2011 using the MEdium Resolution Imaging Spectrometer (MERIS, on board the ENVISAT satellite), with a spatial resolution of 300 m [29]. ...
... These images, with a cross track of 290 km, were acquired in coastal areas (20 km) only, and thus provided very low ocean coverage. The high resolution of this sensor allowed us to observe pixels with quasi-total Sargassum coverage, leading to a very strong red-edge signal, with a maximum reflectance shifted to 800 nm (compared to a maximum around 700 nm for pixel observing Sargassum mixed with water; [38,43]). The FAI index, based on the 833 nm MSI spectral band, associated with the 665 nm and 1610 nm bands, thus seems to be the best suited to detect Sargassum with MSI. ...
... Windrows were formed upwind of the raft that progressively disintegrated. This observation is fully consistent with the 'raft and trail' shape reported by [38], observed under a wind speed of 5 m s -1 . Nevertheless, large rafts (types [4][5] were observed at wind speeds of 4-11 m s -1 . ...
The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m,
VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m2 area) nested within larger ones (of hundreds of km2). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.
... There has been constant progress in the development of remote sensing for floating marine vegetation such as Sargassum species, in order to provide accurate information on their distribution and to quantify their coverage area and biomass (e.g. [21,29,30,[38][39][40][41][42][43][44][45][46][47][48]). The occurrence of large pelagic Sargassum aggregations in the Tropical North Atlantic was first detected from space in 2011 using the MEdium Resolution Imaging Spectrometer (MERIS, on board the ENVISAT satellite), with a spatial resolution of 300 m [29]. ...
... These images, with a cross track of 290 km, were acquired in coastal areas (20 km) only, and thus provided very low ocean coverage. The high resolution of this sensor allowed us to observe pixels with quasi-total Sargassum coverage, leading to a very strong red-edge signal, with a maximum reflectance shifted to 800 nm (compared to a maximum around 700 nm for pixel observing Sargassum mixed with water; [38,43]). The FAI index, based on the 833 nm MSI spectral band, associated with the 665 nm and 1610 nm bands, thus seems to be the best suited to detect Sargassum with MSI. ...
... Windrows were formed upwind of the raft that progressively disintegrated. This observation is fully consistent with the 'raft and trail' shape reported by [38], observed under a wind speed of 5 m s -1 . Nevertheless, large rafts (types [4][5] were observed at wind speeds of 4-11 m s -1 . ...
The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m, VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five-class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m2 area) nested within larger ones (of hundreds of km2). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.
... Ocean surface winds aid in both the aggregation and disintegration of SPDCs. For example, Marmorino et al. [19] found that winds in excess of 5 m s −1 (10 knots) resulted in the disintegration of SPDCs. Within the North Atlantic, the distribution of SPDCs is influenced by the North Equatorial Drift, Caribbean Current, Gulf Stream System, and Canaries Current, which surround the Sargasso Sea [18]. ...
... Sargassum lines may disintegrate during periods of high seasurface wind velocity [19]. Thus, wind velocity may influence our ability to detect Sargassum. ...
... We examined this relationship in three ways. We simply counted the number of scenes with and without SPDC detections above and below the 5 m s −1 threshold noted by Marmorino et al. [19]. Using Spearman's rank correlation test, we examined the correlation between wind velocity and the area of SPDCs observed in each image. ...
Compared with our understanding of most aspects of sea turtle biology, knowledge of the surface-pelagic juvenile life stages remains limited. Young North Atlantic cheloniids (hard-shelled sea turtles) are closely associated with surface-pelagic drift communities (SPDCs), which are dominated by macroalgae of the genus Sargassum. We quantified SPDCs in the eastern Gulf of Mexico, a region that hosts four species of cheloniids during their surface-pelagic juvenile stage. Landsat satellite imagery was used to identify and measure the areal coverage of SPDCs in the eastern Gulf during 2003-2011 (1323 images). Although the SPDC coverage varied annually, seasonally, and spatially, SPDCs were present year-round, with an estimated mean area of SPDC in each Landsat image of 4.9 km
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(SD = 10.1). The area of SPDCs observed was inversely proportional to sea-surface wind velocity (Spearman's r = -0.33, p <; 0.001). The SPDC coverage was greatest during 2005, 2009, and 2011 and least during 2004 and 2010, but the 2010 analysis was affected by the Deepwater Horizon oil spill, which occurred within the study region. In the eastern Gulf, the area of SPDC peaked during June-August of each year. Although the SPDC coverage appeared lower in the eastern Gulf than in other regions of the Gulf and the North Atlantic, surface-pelagic juvenile green, hawksbill, Kemp's ridley, and loggerhead turtles were found to be using this habitat, suggesting that eastern Gulf SPDCs provide developmental habitats that are critical to the recovery of four sea turtle species.
... Gower and King (2011) applied a Maximum Chlorophyll Index to MERIS data (with 709 nm wavelength) for detection of Sargassum. Marmorino et al. (2011) performed airborne hyperspectral and thermal infrared investigations of the Sargassum drift line in waters off the East Coast of Florida, USA. Cui et al. (2012) compared the ability of different satellite data to monitor green macroalgae blooms, including the charge-couple device (CCD) data, SAR data, and spectra radiometer data. ...
... Satellite remote sensing can monitor green macroalgae patches floating on the ocean surface. Presently, the spectral radiometer has been generally applied to monitor green macroalgae blooms from the air and from space (Hu et al., 2010;Gower and King, 2011;Marmorino et al., 2011), but only under cloud free conditions. However, mid latitude areas, such as the Yellow Sea and East China Sea are often covered by cloud. ...
... Unlike the spectral radiometer, which can capture ocean color changes to depths of 10 m beneath the water surface (Marmorino et al., 2011), SAR can only observe the ocean surface. Therefore, the proposed index factors are only applicable to detect macroalgae bloom patches that reach the ocean surface, which show up as bright bands in SAR images due to enhanced strong backscatter. ...
... Cameras were deployed under two types of pelagic sargassum aggregation states: mats and windrows ( Figure 2). Mats were classified as densely packed aggregations of sargassum with an irregular to round shape and measured 5 to 100s of meters in diameter (distance across) (Marmorino et al., 2011;Goodwin et al., 2022). Windrows were defined as aggregations of sargassum generally arranged in a line and ranged from 0.5 meter to several meters in diameter (Marmorino et al., 2011;Goodwin et al., 2022). ...
... Mats were classified as densely packed aggregations of sargassum with an irregular to round shape and measured 5 to 100s of meters in diameter (distance across) (Marmorino et al., 2011;Goodwin et al., 2022). Windrows were defined as aggregations of sargassum generally arranged in a line and ranged from 0.5 meter to several meters in diameter (Marmorino et al., 2011;Goodwin et al., 2022). The term 'raft' is hereinafter used to refer to aggregations of mats and/or windrows. ...
Mass accumulations of pelagic sargassum (Sargassum natans and S. fluitans) in the Tropical Atlantic, across the Caribbean and off the coast of West Africa, are causing extensive ecological and socioeconomic harm. The extraordinary volumes of sargassum influxes could also provide a business opportunity if innovative ways are developed to utilise the raw material. In-water harvesting provides the best opportunity to collect substantial amounts of ‘fresh’ sargassum that can be used in a variety of applications. However, sargassum rafts are living and diverse ecosystems with a range of associated fauna including fish that are targeted by fishers. The consequences of in-water harvesting of sargassum on the biodiversity, including associated fishes, remain poorly understood. Characterisation of this biodiversity within nearshore and offshore environments is needed to help guide best harvest practices and assess possible impacts on fishing opportunities. We assessed the free-swimming fauna associated with sargassum rafts at various distances from shore with the use of underwater video recordings. Over a three-month period, a total of 35 underwater surveys were conducted off the eastern and southern coastline of Barbados. Thirteen species (12 fishes and one comb jelly) from 8 families were identified, with the family Carangidae representing the greatest number of species (n=6). Application of the MaxN metric (maximum number of individuals of a species seen during deployment) revealed significant correlations with raft characteristics notably raft volume, raft distance from shore and water depth. The three environmental variables accounted for 9% of the variation (adjusted R²) in the free-swimming community composition with raft volume being the major driver of species richness. This aligns with ecological theory and supports our hypothesis that larger rafts would host greater species richness. The results demonstrate a strong affiliation between pelagic sargassum rafts and species biodiversity and abundance that will need to be considered by managers when seeking a best compromise between protecting beaches from inundation by sargassum and protecting biodiversity and fishing opportunities.
... These floating mats range greatly in size from small patches less than 0.5 m in horizontal diameter up to huge mats 50 m in diameter [1,4]. Several factors contribute to this broad range in sizes. ...
... Several factors contribute to this broad range in sizes. For example, sustained calm conditions can allow Sargassum mats to form large aggregations, but harsher weather conditions such as high winds can break up large mats of Sargassum or create narrower windrows [4]. As the algae approach the shoreline, wave action can break up mats into significantly smaller sizes. ...
A mutualistic symbiosis exists between the alga Sargassum spp. and two shrimp species, Latreutes fucorum and Leander tenuicornis. However, little is known about how these shrimp locate and establish their host alga. Both visual and chemical cues are potentially available. A previous study has looked at both cue variables with results that are mixed. Specifically, these same shrimp species used chemical cues only when visible cues were available simultaneously. Visual cues would be presumably restricted at night, but chemical cues are potentially available continuously. This current research elaborates on the previous study to fully understand Sargassum shrimp chemoreception. Increases in sample sizes and both a 4-chambered and Y-maze apparatus were used to test whether the shrimp could detect Sargassum cues, dimethylsulfoniopropionate (DMSP) (a chemical excreted by some marine algae), and conspecific cues. Neither shrimp species showed a strong directional response to any of the chemical cues, but the Sargassum and DMSP cues did cause more shrimp to exhibit searching behavior. Additionally, several differences in responses between male and female shrimp were found for each cue. A lowered dilution of DMSP was also tested to determine sensitivity of L. fucorum shrimp to the chemical cue; although searching behavior was triggered, conclusions about quantifying the sensitivity could not be made. Overall, these results show the shrimp can detect chemical cues—in the absence of visual cues—that could affect initiating and maintaining this shrimp/algal symbiosis.
... There is a growing body of research using remote sensing for detecting several species of floating algae, including giant kelp (Augenstein et al., 1991;Bell et al., 2015b;Cavanaugh et al., 2011Cavanaugh et al., , 2010Deysher, 1993;Donnellan and Foster, 1999;Fyfe et al., 1999;Kim et al., 2010), Sargassum (Dierssen et al., 2015;Gower et al., 2006;Gower and King, 2008;Marmorino et al., 2011;Wang and Hu, 2016), and green algae (Cui et al., 2012;Keesing et al., 2011;Ma et al., 2009;Shi and Wang, 2009). In comparison, relatively few studies have used satellite remote sensing to map bull kelp due to the challenge of detecting the generally smaller beds found in close proximity to rocky shorelines (Stekoll et al., 2006). ...
... Alternatively, some studies use data from historical maps, classified aerial photography, and algae harvesting records (Casal et al., 2011;Cavanaugh et al., 2010;Deysher, 1993;Donnellan and Foster, 1999). In some cases, such as the pelagic Sargassum survey by Marmorino et al. (2011), alternatives for field data were not available and accuracy assessment was omitted. Similarly, several studies of the Ulva bloom in the Yellow Sea proceeded without field data (Keesing et al., 2011;Ma et al., 2009), however, local knowledge was used as the bloom was Volent et al. (2007) observed by many vessels during the 2008 Olympic sailing preparations. ...
The distribution and abundance of the canopy-forming kelp Nereocystis luetkeana is of increasing concern for environmental management and conservation in coastal regions due to its importance as a foundation species. Mapping kelp forests aids in understanding their health, productivity, and response to environmental conditions. Remote sensing using satellites is an increasingly accessible tool for mapping nearshore habitats allowing for applications such as long-term monitoring and large- and small-scale surveys. This paper provides a review of passive optical remote sensing techniques for detection and mapping of floating macro-algae, and adapts these techniques for detecting Nereocystis luetkeana, demonstrating their application through a comprehensive case study, from imagery acquisition to map validation. This review with associated case study communicates to non-remote sensing experts a road map to use remote sensing technology for mapping kelp habitats. Keywords: Kelp, Remote sensing, Habitat mapping, Macro algae, Digital image processing, Review
... Traditional remote sensing methods can be used to identify the presence or absence of large mats of floating vegetation (Cavanaugh, Siegel, Kinlan, & Reed, 2010;Gower, Hu, Borstad, & King, 2006;Hu, 2009). Airborne hyperspectral and thermal infrared imagery has also been used to evaluate Sargassum rafts along the Florida Current (Marmorino, Miller, Smith, & Bowles, 2011), but the potential to spectrally discriminate between different types of floating vegetation using remote sensing imagery has yet to be determined. ...
... As vegetation is submerged below the water surface, the spectra will get significantly lower in red and NIR to the point where the enhanced red edge reflectance produced by vegetation is completely absorbed by the water column. From airborne remote sensing, it is difficult to determine whether pixels with only a small NDVI signal occurred because of sparse vegetation, as modeled here, or because they are more deeply submerged in the water column (Marmorino et al., 2011). ...
... Similarly, Dierssen et al. (2015) utilised an airborne imaging spectrometer to distinguish a mass of floating sargassum and seagrass at 1 m resolution. Airborne hyperspectral and thermal infrared imagery has also been used to generate spectra of floating aggregations of submerged sargassum (Marmorino et al., 2011). This high spectral resolution monitoring and mapping technique is commonly used to characterise the reflectance of natural surfaces in a variety of environments such as forest canopies for species identification (for example, Malenovský et al., 2019;Asner et al., 2015), and agriculture for crop health and type (for example Bian et al., 2013;Su, 2020). ...
... Similarly, Dierssen et al. (2015) utilised an airborne imaging spectrometer to distinguish a mass of floating sargassum and seagrass at 1 m resolution. Airborne hyperspectral and thermal infrared imagery has also been used to generate spectra of floating aggregations of submerged sargassum (Marmorino et al., 2011). This high spectral resolution monitoring and mapping technique is commonly used to characterise the reflectance of natural surfaces in a variety of environments such as forest canopies for species identification (for example, Malenovský et al., 2019;Asner et al., 2015), and agriculture for crop health and type (for example Bian et al., 2013;Su, 2020). ...
... En el caso de S. fluitans, su presencia ha sida reportada en centro y Norteamérica, en el sureste y suroeste de Asia, en ciertas islas del Caribe y principalmente en el Atlántico(Széchy et al., 2012).En zonas de calmas, el sargazo forma grandes agrupaciones que describen parches semicirculares cuyos diámetros alcanzan longitudes de hasta 50 m (aproximadamente 2000 m 2 de área). Por otro lado, en condiciones de vientos fuertes, el sargazo tiende a agruparse en dirección del viento describiendo largas filas de menos de 0.5 m de ancho (Figura 2) que se relacionan con las celdas de circulación de Langmuir(Marmorino et al., 2011). ...
The massive arrival of sargassum to the Caribbean and Gulf of Mexico has been reported from 2011 until 2016, nevertheless, during summer 2015 the event was described as extreme and unprecedented. In the Mexican Caribbean, the state of Quintan Roo was severely affected, 9700 m3 of sargassum were collected monthly per kilometer of shore, leaving only 10% of the beaches cleaned (Rodriguez-Martínez et al., 2016). Puerto Morelos reef lagoon was one of the most affected areas, with more than 6 600 m3 per kilometer of sargassum arriving monthly. This resulted in huge piles of decaying organic matter which lead to the eutrophication and pollution of the water due to decomposition by-products. Consequently, nearshore seagrass meadows and coral communities were lost (Silva et al.,2016; van Tussenbroek et al., 2017). On the other hand, the use of heavy machinery caused the compaction and erosion of the beach as well as the destruction of turtle nests. Due to the magnitude of the arrival of sargassum and its effects on the shore, is of utmost importance to understand its origin, the periodicity with which it occurs, as well as the conditions that promote its circulation inside and outside coastal regions. The present work provides relevant information that contribute to the understanding of the last aspect of this phenomenon: its behaviour in a reef lagoon. Sargassum coverage on the beach was estimated from average images from a fixed coastal video monitoring station located in the academic unit Arrecife de Puerto Morelos from the ICMyL, UNAM. Coverage areas were obtained from imagery analysis techniques, the results were rectified in order to obtain real measures for creating a time series of daily coverage values. Several events of arrival and separation of sargassum were registered and linked with measured data of oceanographic variables (wave height, wind speed, sea level). The time series of sargassum accumulation showed two accumulation peaks in September and November. Sargassum maximum coverage was reached on September with more than 8 550 m2 and by December the coverage diminished until 1733m2 of sargassum on average. To characterize better these events, the coupled wave hydrodynamic Delft3D-SWAN model was used using waves and wind as forcing parameters. Discharges were employed to simulate the presence of sargassum ouitside the lagoon. Both modeling and measured data show that during low wind and wave conditions, weak outflows are observed reaching a maximum velocity around 0.096 m/s, resulting in the increase of the residence time of sargassum. On the contrary, under intense wind and waves conditions flows over 0.15 m/s are observed which in turn increases the lagoon dynamics and thus the outflow of sargassum from the system.
... Sargassum (Fucales, Phaeophyceae) are present worldwide in tropical and subtropical environments (Niermann, 1986). All the described Sargassum species are benthic except two pelagic ones: Sargassum natans and Sargassum fluitans, initially reported by C. Columbus (Lapointe and Hanisak, 1985), and mainly confined to the Gulf of Mexico and Sargasso Sea, where they are found accreted together into lines and mats (Marmorino et al., 2011). Even if climatic events (e.g., hurricanes) could spread them onshore, pelagic Sargassum landings in massive amounts were never reported elsewhere than the Caribbean area (Loffler and Hoey, 2017). ...
Massive Sargassum beachings occurred since 2011 on Caribbean shores. Sargassum inundation events currently involve two species, namely S. fluitans and S. natans circulating and blooming along the North Atlantic subtropical gyre and in the entire Caribbean region up to the Gulf of Mexico. Like other brown seaweeds, Sargassum have been shown to bioaccumulate a large number of heavy metals, alongside with some organic compounds including the contamination by historical chlordecone pollution in French West Indies (FWI), an insecticide used against the banana’s weevil Cosmopolites sordidus. The present study reports, during two successive years, the concentration levels of heavy metals including arsenic in Martinique and Guadeloupe (FWI). We found that Sargassum can also accumulate a high concentration of chlordecone. Sargassum contamination by chlordecone is observed in areas close to contaminated river mouth but can be partly due to chlordecone desorption when secondary drifted on chlordecone-free shore. Our results further demonstrate that algae bleaching raises a number of questions about inorganic and organic pollutant (i) bioaccumulation, at sea for arsenic and close to river plumes for chlordecone, (ii) transport, and (iii) dissemination, depending the shoreline and the speciation for arsenic and/or metabolization for both.
... Sargassum (Fucales, Phaeophyceae) are present worldwide in tropical and subtropical environments (Niermann, 1986). All the described Sargassum species are benthic except two pelagic ones: Sargassum natans and Sargassum uitans, initially reported by C. Columbus (Lapointe and Hanisak, 1985), and mainly con ned to the Gulf of Mexico and Sargasso Sea where they are found accreted together into lines and mats (Marmorino et al., 2011). Even if climatic events (e.g. ...
Massive Sargassum beachings occur since 2011 on Caribbean shores. Sargassum inundation events currently involve two species, namely S. fluitans and S. natans that are circulating and blooming along the North Atlantic subtropical gyre and in the entire Caribbean region up to the Gulf of Mexico. Alike other brown seaweeds, Sargassum have been shown to bioaccumulate a large number of heavy metals, alongside with some organic compounds including the contamination by historical chlordecone pollution in French West Indies (FWI), an insecticide used against the banana’s weevil Cosmopolites sordidus. The present study reports, during two successive years, the concentration levels of heavy metals including arsenic in Martinique and Guadeloupe (FWI). We found that Sargassum can also accumulate high concentration of chlordecone. Sargassum contamination by chlordecone is observed in areas that are close to contaminated river mouth. Our results further demonstrate that algae bleaching raises a number of questions about inorganic and organic pollutants bioaccumulation, transport and dissemination.
... Research which appeared to focus on specific events generally collected evidence of Sargassum immediately after or in response to the emergence of a bloom over water bodies or the appearance of Sargassum mats in coastal or beach areas. For example, in response to a bloom off the coast of Florida, Marmorino et al (2011) [39] used airborne imagery to collect evidence of the Sargassum raft. Similarly, Oyesiku and Egunyomi (2014) [46] responded to reports of Sargassum in Nigeria by visiting the site and collecting samples. ...
Sargassum algal blooms on ocean surfaces and landings of huge Sargassum mats on beaches is an emerging global environmental challenge with wide socio-economic and environmental implications. Literature on Sargassum growth cycles, travel patterns, species and morphotypes, and quantified impacts have tended to focus on a geographic region, or a specific event. Few, if any, publications document long term continuous monitoring of Sargassum blooms in large areas such as the Pacific, or the tropical Atlantic. To address this gap, this paper systematically reviews the global evidence of Sargassum bloom monitoring beyond the Sargasso Sea, and identifies gaps in the evidence base of floating and landing influxes. This systematic review uses combinations of two key terms relating to Sargassum and monitoring, and utilises the resources in ISI Web of Knowledge, Scopus and Google Scholar. The analysis moves us past a classic literature review, and produces an unbiased assessment of empirical research on Sargassum monitoring from 1960 to 2019. We find a significant research focus on open-ocean blooms and floating mats whereas research on beach landings and their associated impacts is comparatively limited. Research is focused within specific countries or water bodies (notably, the Gulf of Mexico, the Caribbean and North Atlantic Ocean) and tends not to comprehensively assess neighbouring or regional shorelines, for example, West Africa and Central America. There was a lack of consistency in the application of methods for quantifying Sargassum biomass volume (including dry/wet weight, unit of measurement, and spatial extent of calculations). Further, in many publications Sargassum species identification was omitted. Given current attempts to understand the drivers and impacts of the exponential growth in Sargassum in some parts of the world, a consistent and replicable research approach to monitoring Sargassum could support creation of a Sargassum evidence database. To move this agenda forwards, we propose a definition for a Sargassum 'event': a continuous bloom of any Sargassum in open oceans, or, an aggregation of landed Sargassum, with the potential to disrupt social, economic or ecosystem functioning, or to impact human health. This review highlights the importance of standardising Sargassum monitoring methods to facilitate improved documentation of temporal and spatial patterns of Sargassum blooms and beach landings.
... Winds, waves and currents aggregate these surface drifters into configurations that range from widely dispersed clumps to large neustonic rafts tens of meters wide and windrows that extend across the ocean surface for tens of kilometres (e.g. Marmorino et al., 2011;Ody et al., 2019). In the Sargasso Sea, the pelagic Sargassum taxa are part of the natural ecosystems in the mid-Atlantic. ...
... Winds, waves and currents aggregate these surface drifters into configurations that range from widely dispersed clumps to large neustonic rafts tens of meters wide and windrows that extend across the ocean surface for tens of kilometres (e.g. Marmorino et al., 2011;Ody et al., 2019). In the Sargasso Sea, the pelagic Sargassum taxa are part of the natural ecosystems in the mid-Atlantic. ...
... The study showed that satellite water colour image could be used to visualize sea surface and coastal chlorophyll concentration patterns. Furthermore, Marmorino et al. (2011) were able to detect Sargassum rafts occurrence over Florida Current using Airborne hyperspectral and thermal infrared imagery. described Sargassum distributions patterns in the Northern Atlantic Ocean (area off North Brazil, from the Caribbean to the West African coast), by using the Medium Resolution Imaging Spectrometer (MERIS) images and Moderate Resolution Imaging Spectroradiometer (MODIS) on which they perform maximum chlorophyll index (MCI) and MODIS Red Edge (MRE) similar to the Floating Algae Index (FAI). ...
Since 2011, large amounts of seaweed Sargassum species were observed in sea water and on West African beaches, among them the Nigerian coast which is significantly affected. Through satellite observations, based on fluorescence values (0.2 – 0.3 W·m −2·μm −1 ·sr −1 ), we were able to detect recurrent occurrence of Sargassum throughout these last years in Nigeria. GPS coordinates from previous studies and satellite imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS Aqua) were used to monitor the expansion Sargassum patterns from 2011 to 2016. During this period, the fluorescence spread along the Eastern to Western coasts, and the seasonal distribution resulted in difficulties impacting the livelihood of the population. Consequently, fishery, tourism activities and food security are threatened. However, further studies using remote sensing techniques need to done in order to differentiate the species and appropriately estimate the masses.
... Mid-and long-wave infrared (electromagnetic wavelengths ranging from 3 to 14 µm) imagery was found to be an effective remote sensing tool, capable of visualizing upper ocean hydrodynamics with unparalleled detail. A growing number of airborne studies [10][11][12][13][14][15][16] demonstrated the power of this remote sensing modality to detect and image a wide variety of dynamical processes taking place at or below the air-sea interface. A mid-or long-wave infrared camera is capturing passive radiation emitted by the water no deeper than the skin layer, i.e., tens of microns. ...
This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1–14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and to reference depths of retrieved currents.
... Winds, waves and currents aggregate these surface drifters into configurations that range from widely dispersed clumps to large neustonic rafts tens of meters wide and windrows that extend across the ocean surface for tens of kilometres (e.g. Marmorino et al., 2011;Ody et al., 2019). In the Sargasso Sea, the pelagic Sargassum taxa are part of the natural ecosystems in the mid-Atlantic. ...
... Pelagic Sargassum, a complex of two co-occurring species of floating marine brown macroalgae (Sargassum natans, Sargassum fluitans; Class Phaeophyceae), is commonly found in surface waters of the Sargasso Sea and the northwestern Gulf of Mexico (GOM) (Lapointe 1995, Gower andKing 2008), areas where ocean eddies tend to retain and consolidate deployed surface drifters. Winds and ocean currents aggregate the Sargassum into large neustonic rafts tens of meters wide (Marmorino et al. 2011) and weed lines (windrows) that extend across the ocean surface for tens of kilometers (Butler et al. 1983, Hu et al. 2105, Hu et al. 2016). These Sargassum features provide habitat for a large and diverse assemblage of marine organisms (Coston-Clements et al. 1991, Wells and Rooker 2004, Hoffmayer et al. 2005, Hallett, 2011, Huffard et al. 2014) but may also raft invasive species. ...
... When a raft starts to disintegrate due to abiotic factors or intense grazing, mobile rafters may abandon the sinking raft and hop onto nearby, intact rafts; this process has been suggested by Hobday (2000b) for mobile fauna capable of swimming. Macrophyte rafts are not homogeneously distributed in the ocean, but rather are usually concentrated in frontal systems and drift rows (Hinojosa et al. 2010, Marmorino et al. 2011, Witherington et al. 2012). In such situations, large numbers of fl oating macrophytes of all ages and successional stages come together, offering ample opportunity for mobile organisms to move between rafts. ...
... However, these pixels are not counted in long-term statistics, thus would have minimal impacts on the statistical results once sufficient number of images is used in the statistics. On the other hand, non-optimal observing conditions such as variable winds and currents may have significant impacts on the statistical results (Gower & King, 2011;Marmorino, Miller, Smith, & Bowles, 2011;Szekielda, Marmorino, Bowles, & Gillis, 2010;Woodcock, 1993). Under high winds, Sargassum may be dissipated and become undetectable to MODIS imagery while they may still be observed in high-resolution airborne imagery or field sampling through neuston net tows. ...
Sargassum washing ashore on the beaches of the Caribbean Islands since 2011 has caused problems for the local environments, tourism, and economies. Although preliminary results of Sargassum distributions in the nearby oceans have been obtained using measurements from the Medium Resolution Imaging Spectrometer (MERIS), MERIS stopped functioning in 2012, and detecting and quantifying Sargassum distributions still face technical challenges due to ambiguous pixels from clouds, cloud shadows, cloud adjacency effect, and large-scale image gradient. In this paper, a novel approach is developed to detect Sargassum presence and to quantify Sargassum coverage using the Moderate Resolution Imaging Spectroradiometer (MODIS) alternative floating algae index (AFAI), which examines the red-edge reflectance of floating vegetation. This approach includes three basic steps: 1) classification of Sargassum-containing pixels through correction of large-scale gradient, masking clouds and cloud shadows, and removal of ambiguous pixels; 2) linear unmixing of Sargassum-containing pixels; and, 3) statistics of Sargassum area coverage in pre-defined grids at monthly, seasonal, and annual intervals. In the absence of direct field measurements to validate the results, limited observations from the Hyperspectral Imager for the Coastal Ocean (HICO) measurements and numerous local reports support the conclusion that the elevated AFAI signals are due to the presence of Sargassum instead of other floating materials, and various sensitivity analyses are used to quantify the uncertainties in the derived Sargassum area coverage. The approach was applied to MODIS observations between 2000 and 2015 over the Central West Atlantic (CWA) region (0–22°N, 63–38°W) to derive the spatial and temporal distribution patterns as well as the total area coverage of Sargassum. Results indicate that the first widespread Sargassum distribution event occurred in 2011, consistent with previous MERIS findings. Since 2011, only 2013 showed a minimal Sargassum coverage similar to the period of 2000 to 2010; all other years showed significantly more coverage. More alarmingly, the summer months of 2015 showed mean coverage of > 2000 km2, or about 4 times of the summer 2011 coverage and 20 times of the summer 2000 to 2010 coverage. Analysis of several environmental variables provided some hints on the reasons causing the inter-annual changes after 2010, yet further multi-disciplinary research (including in situ measurements) is required to understand such changes and long-term trends in Sargassum coverage.
... 20 %- Thiel and Gutow 2005a). Rafting suspension feeders benefit from the concentration of their rafts and suspended organic material in surface 6 Marine Litter as Habitat and Dispersal Vector fronts generated by the convergence of surface waters, wind-induced Langmuir cells and other surface features (Woodcock 1993;Marmorino et al. 2011). The accumulation of suspended matter and nutrients in these convergence zones apparently fuels diverse rafting communities on floating abiotic substrata, which also encompass primary producers, herbivores, and predators. ...
Identifying and eliminating the sources of microplastic to habitats is crucial to reducing the social, environmental and economic impacts of this form of debris. Although eliminating sources of pollution is a fundamental component of environmental policy in the U.S.A. and Europe, the sources of microplastic and their pathways into habitats remain poorly understood compared to other persistent, bioaccumulative and/or toxic substances (i.e. priority pollutants; EPA in U.S. Environmental Protection Agency 2010–2014 Pollution Prevention (P2) Program Strategic Plan. Washington, USA, pp. 1–34, 2010; EU in Official J Eur Union L334:17–119, 2010). This chapter reviews our understanding of sources and pathways of microplastic, appraises terminology, and outlines future directions for meaningfully integrating research, managerial actions and policy to understand and reduce the infiltration of microplastic to habitats. © 2015, Springer International Publishing. All Rights Reserved.
... 20 %- Thiel and Gutow 2005a). Rafting suspension feeders benefit from the concentration of their rafts and suspended organic material in surface fronts generated by the convergence of surface waters, wind-induced Langmuir cells and other surface features (Woodcock 1993;Marmorino et al. 2011). The accumulation of suspended matter and nutrients in these convergence zones apparently fuels diverse rafting communities on floating abiotic substrata, which also encompass primary producers, herbivores, and predators. ...
Floating anthropogenic litter provides habitat for a diverse community of marine organisms. A total of 387 taxa, including pro- and eukaryotic micro-organisms, seaweeds and invertebrates, have been found rafting on floating litter in all major oceanic regions. Among the invertebrates, species of bryozoans, crustaceans, molluscs and cnidarians are most frequently reported as rafters on marine litter. Micro-organisms are also ubiquitous on marine litter although the composition of the microbial community seems to depend on specific substratum characteristics such as the polymer type of floating plastic items. Sessile suspension feeders are particularly well-adapted to the limited autochthonous food resources on artificial floating substrata and an extended planktonic larval development seems to facilitate colonization of floating litter at sea. Properties of floating litter, such as size and surface rugosity, are crucial for colonization by marine organisms and the subsequent succession of the rafting community. The rafters themselves affect substratum characteristics such as floating stability, buoyancy, and degradation. Under the influence of currents and winds marine litter can transport associated organisms over extensive distances. Because of the great persistence (especially of plastics) and the vast quantities of litter in the world’s oceans, rafting dispersal has become more prevalent in the marine environment, potentially facilitating the spread of invasive species. © 2015, Springer International Publishing. All Rights Reserved.
... Indeed, such a reflectance trough has also been reported in Dierssen et al. (2015) from field measurements and by several airborne missions. In addition to the PHILLS measurements over the Florida Keys (Szekielda et al., 2010), Marmorino, Miller, Smith, and Bowles (2011) used a Compact Airborne Spectro-graphic Imager (CASI) on an aircraft to measure hyperspectral signal between 400 and 1000 nm from Sargassum rafts off SE Florida, and showed a spectral trough around 625 nm. Mehrtens et al. (2009) used an AISA Eagle (AWI) hyperspectral sensor (400-970 nm, 2.9 nm) on a motor glider to measure Sargassum and other seaweed rafts near the island of Helgoland (Germany, North Sea), and also reported a spectral trough around 625 nm. ...
Remote detection of pelagic Sargassum is often hindered by its spectral similarity to other floating materials and by the inadequate spatial resolution. Using measurements from multi-spectral satellite sensors (Moderate Resolution Imaging Spectroradiometer or MODIS), Landsat, WorldView-2 (or WV-2) as well as hyperspectral sensors (Hyperspectral Imager for the Coastal Ocean or HICO, Airborne Visible-InfraRed Imaging Spectrometer or AVIRIS) and airborne digital photos, we analyze and compare their ability (in terms of spectral and spatial resolutions) to detect Sargassum and to differentiate it from other floating materials such as Trichodesmium, Syringodium, Ulva, garbage, and emulsified oil. Field measurements suggest that Sargassum has a distinctive reflectance curvature of ~ 630. nm due to its chlorophyll c pigments, which provides a unique spectral signature when combined with the reflectance ratio between brown (~ 650. nm) and green (~ 555. nm) wavelengths. For a 10-nm resolution sensor on the hyperspectral HyspIRI mission currently being planned by NASA, a stepwise rule to examine several indexes established from 6 bands (centered at 555, 605, 625, 645, 685, 755. nm) is shown to be effective to unambiguously differentiate Sargassum from all other floating materials Numerical simulations using spectral endmembers and noise in the satellite-derived reflectance suggest that spectral discrimination is degraded when a pixel is mixed between Sargassum and water. A minimum of 20-30% Sargassum coverage within a pixel is required to retain such ability, while the partial coverage can be as low as 1-2% when detecting floating materials without spectral discrimination. With its expected signal-to-noise ratios (SNRs ~ 200:1), the hyperspectral HyspIRI mission may provide a compromise between spatial resolution and spatial coverage to improve our capacity to detect, discriminate, and quantify Sargassum.
... In the N Atlantic, pelagic Sargassum has been observed in such windrows extending over tens to hundreds of miles (Carr 1986). Drift lines of floating Sargassum are transient structures that disintegrate when wind exceeds a certain threshold speed (Marmorino et al. 2011). Johnson and Richardson (1977) suggested that the downwelling of surface waters in the zones of convergence might carry Sargassum below a critical depth where the thalli lose buoyancy and finally sink to the seafloor, thereby exporting biomass from the surface to the deep sea benthos (Schoener and Rowe 1970). ...
... In the N Atlantic, pelagic Sargassum has been observed in such windrows extending over tens to hundreds of miles (Carr 1986). Drift lines of floating Sargassum are transient structures that disintegrate when wind exceeds a certain threshold speed (Marmorino et al. 2011). Johnson and Richardson (1977) suggested that the downwelling of surface waters in the zones of convergence might carry Sargassum below a critical depth where the thalli lose buoyancy and finally sink to the seafloor, thereby exporting biomass from the surface to the deep sea benthos (Schoener and Rowe 1970). ...
A wide diversity of floating seaweeds is found in temperate and subpolar regions of the world’s oceans where sea surface currents and winds determine their traveling velocities and directions. The importance of floating seaweeds as dispersal agents for associated organisms and for the algae themselves varies depending on the supply from benthic source populations and on their persistence at the sea surface. Persistence of floating algae depends on water temperature, grazing activity, epifaunal load, and, to a lesser extent, on prevailing irradiance conditions. In temperate regions, persistence of floating algae is primarily limited by warm sea surface temperatures and high densities of motile and sessile epifauna whereas at higher latitudes algae can successfully compensate grazer-induced tissue loss by continuous growth at the prevailing low water temperatures. Accordingly, floating seaweeds can bridge large oceanic distances especially at high latitudes allowing for connectivity among distant benthic populations of algae and associated rafters.
... This was achieved here with airborne assessment of algal biomass, but only on one particular day. This is an opportunistic study, similar to the processing of a disintegrating Sargassum raft previously observed with an airbone hyperspectral sensor in the ocean (Marmorino et al. 2011) and the observations of rafts by Belsher et al. (1990) in Moorea using 20-m resolution SPOT multispectral images. The potential optical remote sensing for monitoring algal rafts is high, but warrants further investigation. ...
The proliferation of two native brown algae, Turbinaria ornata and Sargassum pacificum, was observed on high islands of French Polynesia since the early 1980s. High swells frequently remove algae from their substratum, floating algae concentrate due to local currents in specific lagoon locations, and large compact rafts eventually form. A study of the prospective industrial use of drifting algae was conducted, including estimates of biomass, biomass renewal and agronomical trials. Harvesting rafts could efficiently limit the geographic expansion of proliferating populations and their associated nuisance. The drifting biomass in rafts around Moorea Island was estimated at 13,062 ± 1,998 kg dry mass based on aerial photographs acquired on 31 August 1997. To measure the renewal rate and temporal variation of the raft biomass, we completely harvested one of the larger rafts in February 2002, which was quickly renewed within 10 days. In situ and airborne assessments of biomass show a range of variation between 178 kg and 8.5 t of dry algae. Steady resource availability is required for industrial exploitation, and we demonstrate that drifting algae represent a valuable and significant renewable resource for French Polynesia. Moreover, agronomical enrichment trials using drifting algae as organic additives gave promising perspectives for agriculture uses, with an increase in size, dry mass and root development for maize plants.
... The Sargasso Sea is bisected by the subtropical convergence zone (STCZ), a frontal region which is often associated with increased productivity (Andersen et al. 2011). Sargassum floating on the surface ranges in size from fist-sized clumps to massive rafts tens of meters in diameter (Marmorino et al. 2011) forming contiguous features possibly extending 100 miles or more (Carr 1986). ...
Pelagic forms of the brown algae (Phaeophyceae) Sargassum spp. and their conspicuous rafts are defining characteristics of the Sargasso Sea in the western North Atlantic. Given rising temperatures and acidity in the surface ocean, we hypothesized that macrofauna associated with Sargassum in the Sargasso Sea have changed with respect to species composition, diversity, evenness, and sessile epibiota coverage since studies were conducted 40 years ago. Sargassum communities were sampled along a transect through the Sargasso Sea in 2011 and 2012 and compared to samples collected in the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone from 1966 to 1975. Mobile macrofauna communities exhibited changes in community structure and declines in diversity and evenness within a 6-month time period (August 2011–February 2012). Equivalent declines in diversity and evenness were recorded in the same region (Sargasso Sea, 25°–29°N) in 1972–1973. Recent community structures were unlike any documented historically, whether compared to sites of the same latitude range within the Sargasso Sea, or the broader historical dataset of sites ranging across the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone. Recent samples also recorded low coverage by sessile epibionts, both calcifying forms and hydroids. The diversity and species composition of macrofauna communities associated with Sargassum might be inherently unstable. While several biological and oceanographic factors might have contributed to these observations, including a decline in pH, increase in summer temperatures, and changes in the abundance and distribution of Sargassum seaweed in the area, it is not currently possible to attribute direct causal links.
Electronic supplementary material
The online version of this article (doi:10.1007/s00227-014-2539-y) contains supplementary material, which is available to authorized users.
... First, climate change will influence rates of raft destruction by altering wave and wind climate. The persistence of floating material is inversely related to water and wind motion; increases in either of these forces tend to lead to fragmentation of raft aggregations (Marmorino et al. 2011). Climate models predict significant increases in wave height and wind speed in some regions (e.g. ...
Most models predicting changes to species distributions under future climate scenarios ignore dispersal processes, despite their importance in determining community structure in both terrestrial and aquatic systems ('supply-side ecology'). In the marine environment, facilitation of long-distance dispersal of coastal organisms by macrophytic rafts may be severely modified by climate impacts on raft supply, quality, and persistence, and on transport processes. Increasing storminess in the coastal zone, higher water temperatures, and changes in water circulation represent some of the key mechanisms that will directly affect rafts, while increases in herbivore metabolism due to higher water temperatures are likely to indirectly reduce raft longevity through raft consumption. Accurate predictions of climate impacts on coastal biodiversity will be contingent on resolution of factors influencing rafting so that this and other dispersal mechanisms can be incorporated into species distribution models.
Since 2011, massive new strandings of holopelagic Sargassum have been reported on the coasts of the Caribbean, northern Brazil, Guiana, and West Africa, causing severe economic and ecological damage. Three common morphotypes (S. fluitans III, S. natans I, and S. natans VIII) were identified as responsible for these catastrophic events, with dominance shifts between them over time. However, the taxonomic status of these holopelagic Sargassum morphotypes remains unclear. Using an integrative taxonomy framework, combining a morphological study and molecular analyses, this study aimed to clarify their taxonomic status. Morphological analyses of 54 characters revealed no intermediate form between the three morphotypes, with the overall shape, nature of the axis, and size and shape of blades and vesicles being the most discriminating. An analysis of mitochondrial (IGS, cox2, cox3, mt16S rRNA, and nad6) and plastid (rbcL) markers confirmed the genetic divergence among the three morphotypes, with a lower level of divergence between the two S. natans morphotypes. Without additional molecular characterization, these morphotypes cannot be classified as three distinct species. However, due to their distinct morphological characteristics and sympatry within drifting aggregations, a revision of holopelagic species names is proposed, with Sargassum fluitans var. fluitans (for S. fluitans III), Sargassum natans var. natans (for S. natans I), and S. natans var. wingei (for S. natans VIII). This revision provides necessary clarity on the species involved in inundations of the tropical Atlantic.
Article La retirada de restos vegetales de Sargassum spp. depositados sobre la playa emergida constituyen una parte de la limpieza de playas en el Caribe. Estas gestiones realizadas a lo largo de las últimas décadas han dado lugar a la pérdida de superficies y volúmenes de playa y dunas. El estudio analiza los volúmenes de sedimento retirados mediante la limpieza de Sargassum spp. en 12 playas de México y República Dominicana, cuantificando el volumen total en 18.987,3 m 3 , con un 61,23 % de sedimento intercalado, equivalente a 9.872,36 T de arena. Este tipo de ges-tión supone un impacto geomorfológico continuo con una importante pérdida de sedimento anual que afecta a la estabilidad del balance sedimentario del sistema playa. Palabras clave: Caribe, Sargassum spp., limpieza de playas, erosión. Loss of sediment associated with the removal of deposits of Sargassum spp. on the beaches of the Caribbean Part of the cleaning of beaches in the Caribbean islands involves the removal of Sargassum spp. that remains deposited on the emerged beach and dunes. The study analyses the volumes of sediment removed with the Sar-gassum spp. at 12 beaches in México and the Dominican Republic, quantifying the volume of material removed at 18,987.3 m 3 , of which an estimated 61.23 % (or 9,872.36 T) was sand. This kind of management involves a continuous geomorphological impact with an important loss of sediment that affects the stability of the sedimentary balance of the beach system. El turismo de sol y playa es la modalidad que mayores flujos genera a escala internacional y supone una importante aportación al producto interior bruto (PIB) en países denominados turísticos. En el Caribe, México y República Dominicana son unos de los principales destinos turísticos de este tipo con una aportación al PIB de 8,7 y 8,4 % respectivamente, y modelos turísticos basados en el producto turístico litoral. Para mantener una playa a largo plazo, el balance debe ser positivo, o al menos equilibrado, ya que los balances negativos en última instancia causan su erosión (Komar, 1999). La presión derivada de la industria turística ha hecho que muchos ambientes sedimentarios litorales se hayan visto gravemente afectados a lo largo de la costa. Los ambientes litorales de México y República Dominicana (Fig. 1) están some-tidos desde hace décadas a una problemática geoam-biental asociada a su uso y explotación (Peynador & Méndez-Sánchez, 2010; Roig-Munar et al., 2018; Guima-rais et al., 2021), pero en la última década presentan la llegada y varado masivo de sargazo, la gestión de su retirada generando impactos geoambientales con pérdida de superficie y volumen de playa. Una de las preocupaciones fundamentales nace inicialmente desde el sector turístico en la región del Caribe por la afectación que implican las grandes masas de sargazo Pérdida de sedimento asociada a la retirada de depósitos de Sargassum spp. en las playas del Caribe
This article reviews the broad range of contemporary remote sensing technologies that can access the ocean, while emphasizing next-generation ones that might revolutionize the field. Significant challenges remain in studying the largest part of Earth's biosphere. As of 2022, less than 10% of the ocean has been imaged at a comparable resolution to the surface of the moon and Mars, despite comprising more than 90% of the habitable volume of our planet. Within the past five years, phenomena as modest as refractive ocean-wave distortion have finally been addressed, but steep technology maturation and challenges persist in remote sensing life in our oceans, hampering our understanding of rapidly changing ecosystems at a crucial inflection point in our history. We survey the field and share emerging technologies and trends, while motivating the case for a future Sustained Marine Imaging Program for the next decade in remote sensing the ocean biosphere.
Expected final online publication date for the Annual Review of Environment and Resources, Volume 47 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Recently there has been a significant increase in the amount and frequency of seaweed blooms of the holopelagic brown macroalgae Sargassum fluitans and natans (hereafter Sargassum) in the Atlantic Ocean. These blooms impose a major burden on residents (e.g. rotting beached Sargassum, unpleasant odor, toxic gases), the local economy of countries with affected coast lines (e.g. impacting tourism and aquaculture, costs for remediation), and have a significant impact on the environment (e.g. beaches and coastal areas) and local marine wildlife. Here we present a Techno-Economic Analysis to demonstrate how this burden can be turned into an economic, social and environmental asset. The suggested process involves sustainable ship-based harvesting of excess biomass (up to 6.3 MT·year⁻¹) and using hydrothermal liquefaction (HTL) and established fuel refining processes to deliver renewable liquid fuels. Sea-based harvesting of Sargassum addresses the primary cost impediment for algae-based renewable fuel production, reducing capital and operating costs by 78% and 66% respectively compared with currently modelled land-based microalgae renewable fuel production processes. The modelled approach charts a path to cost competitive renewable fuels that reduce CO2 emissions while mitigating the economic, social and environmental problems caused by these large Sargassum algae blooms. The financial analysis of the process yielded an Internal Rate of Return (IRR) between 2.4% and 28.1% based on the scenarios analyzed. The process could generate up to 8500 bbl of crude oil per day profitably at US$43 bbl⁻¹ (10% IRR), equivalent to 470 ML of diesel or jet fuel per year as well as biofertilizers and recycled nutrients, employ around 200 direct personnel and create up to 1000 indirect jobs.
Las arribazones anómalas de sargazo a costas del Atlántico se han convertido en poco
tiempo en un problema ambiental y socioeconómico, con causas multifactoriales del
que todavía se tiene un sinnúmero de preguntas sin responder. Este capítulo ofrece
una revisión general del tema, con una descripción global de lo que es el sargazo
pelágico, sus especies, hábitat y ecosistema natural, así como las posibles causas de
su transformación en una especie silvestre que se ha tornado perjudicial en grandes
acumulaciones en zonas costeras sensibles. Se incluye una hipótesis de la asociación
que existe entre el crecimiento y dispersión anómalos del sargazo y los fenómenos atmosféricos interdecadales. Posteriormente, se ofrece una revisión de la detección
satelital imprescindible para el monitoreo del problema y una primera aproximación
a indicadores de los impactos potenciales en las áreas ecológicamente sensibles de las
costas en el Caribe mexicano. Finalmente, se reseña la corta historia del problema en México y los pormenores que se han suscitado para gestar un plan de manejo y
contención que integre a todos los sectores de la sociedad. Se reconoce que hasta el
momento no se ha logrado amalgamar el conocimiento de los grupos con experiencia
en el tema y se recomienda a los tomadores de decisiones gestar un verdadero esquema
de monitoreo continuo y, de forma imprescindible, invertir en investigación para
la predicción, prevención, manejo y disposición final adecuados de las arribazones
masivas de sargazo.
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Using high-resolution airborne measurements and more synoptic coverage of Landsat measurements, we estimated the total Sargassum coverage in the northeastern Gulf of Mexico (NE GOM) during 2010, with the ultimate purpose to infer how much Sargassum might have been in contact with oil from the Deepwater Horizon oil spill. Mean Sargassum coverage during the four quarters of 2010 for the study region was estimated to range from ~ 3148 ± 2355 km2 during January–March to ~ 7584 ± 2532 km2 during July–September (95% confidence intervals) while estimated Sargassum coverage within the integrated oil footprint ranged from 1296 ± 453 km2 (for areas with > 5% thick oil) to 736 ± 257 km2 (for areas with > 10% thick oil). Similar to previous studies on estimating Sargassum coverage, a direct validation of such estimates is impossible given the heterogeneity and scarcity of Sargassum occurrence. Nonetheless, these estimates provide preliminary information to understand relative Sargassum abundance in the NE GOM.
Abstract
Systematic molecular studies have not been performed on ecologically important brown algae (Sargassum) in the Gulf of California, Mexico, where 42 specific and infraspecific names have been recorded within this genus. We conducted phylogenetic analyses of nuclear ribosomal ITS and mitochondrial cox1 and cox3 sequences, along with detailed morphological observations of Sargassum collected in the Gulf of California. We confirmed the presence of six species, five previously described—S. herporhizum, S. horridum, S. johnstonii, S. lapazeanum, and S. sinicola, as well as the newly described Sargassum ulixei sp. nov. which is characterized by terete primary axes arising from the stipe, lanceolate to elliptical sessile ecostate blades with smooth margins, cryptostomata, ellipsoidal vesicles with a short mucron, and cylindrical to ellipsoidal receptacles. The individual analyses and subsequent phylogenetic analysis recognized two groups previously described by Dawson, one as Sargassum and other as Horridum. Our studies suggest that the Gulf of California is a region with endemic Sargassum species, and is clearly distinguished from the Pacific side of Baja California, where recently introduced species are common. Based on phylogenetic relationships, we propose two geographical origins for the Sargassum from the Gulf of California: a first group originating from the proto-Gulf, related to species from the northern hemisphere (including five species); and a second group, containing S. sinicola, introduced when the southern end opened at a later stage.
Drifting reefs of Sargassum (a brown alga) are used by a variety of pelagic seabirds in the western Atlantic Ocean. We examined gut contents from 964 individuals of 39 seabird species collected 5 to 60 km off the coast of North Carolina for evidence of Sargassum use. Sargassum pieces or Sargassum-associated prey were found in nine of 10 Procellariiformes species and less frequently among Charadriiformes (12 of 25 species). No Sargassum-associated prey was found in Pelecaniformes examined, but observational data indicated that Atlantic tropicbirds (Phaethon lepturus and P. aethereus) and Masked Boobies (Sula dactylatra) commonly foraged over Sargassum. Four species were considered Sargassum specialists, having frequencies of occurrence >25% and high volumes of Sargassum-associated prey: Audubon's Shearwater (Puffinus Iherminieri), Royal Tern (Thalasseus maximus), Bridled Tern (Onychoprion anaethetus), and Red-necked Phalarope (Phalaropus lobatus). Seven species fed in Sargassum to a lesser extent, and nine species had ingested Sargassum pieces, but contained no Sargassum-associated prey. It is likely that other seabird species forage regularly over Sargassum, as our conclusions are based on relatively small sample sizes taken during random sampling in the open ocean. Our conservative analysis and extensive observational data indicate the Sargassum community is critical for feeding for some western North Atlantic seabirds. Degradation of Sargassum habitats by oil development, harvest, and/or ocean acidification would undoubtedly have negative effects on fitness of these birds.
In our experience, as data from every deployment are processed and analyzed, new questions emerge. This implies that, even after decades of excellent work by many researchers, the use of high resolution thermal imaging to address the types of phenomena discussed here, and others, is still in fact at an early stage and will remain a fruitful field of study.
Off the SE US coast seabirds were significantly more abundant in waters with large (>5 m2) patches of the alga, and mean avian density was 32-43 times greater in waters where Sargassum was present than in adjacent waters without the alga. Some 23 seabird species foraged at Sargassum. Significantly >50% of white-tailed tropicbirds Phaethon lepturus, masked boobies Sula dactylatra and bridled terns Sterna anaethetus were observed at algal patches. Species that use aerial-dipping and plunge-diving foraging behaviours displayed athe greatest affinity for Sargassum. Large-bodied seabirds (large shearwaters, tropicbirds, boobies) generally were found at large patches, white small-bodied species (phalaropes and Puffinus lherminieri) occurred at smaller patches. Seasonal abundance of the pelagic bridled tern corresponded to seasonal variation in Sargassum abundance. Most seabirds associated with Sargassum for foraging, but bridled and black terns Chlidonias niger also used large lagal mats for roost sites. -from Author
Intense plankton blooms (colloquially called ‘red tides’) are becoming an increasingly important phenomenon in coastal waters. This Letter shows how the European satellite sensor MERIS (Medium Resolution Imaging Spectrometer) can be used to detect a peak in the optical spectrum of water‐leaving radiance near 705 nm which provides a more specific response to some types of these blooms. Images and spectra are presented, derived from a MERIS scene where small areas have this response. One such area is at the site of a fish farm where bloom conditions were confirmed by surface observations and measurements. The observed spectra are compared to model results to demonstrate how these responses arise. Inspection of data from other parts of the world shows similar features in US and European waters.
Author Posting. © Sears Foundation for Marine Research, 2007. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 65 (2007): 117-145, doi:10.1357/002224007780388702. Accumulation and transport of plankton in fronts propagating across-shore is a process of considerable ecological importance for many inhabitants of the littoral zone, since it links the offshore larval pool with the juvenile and adult inshore habitat. Several field studies have shown that larval plankton accumulates in fronts, but have failed to give a conclusive proof that effective Lagrangian transport takes place. A few process-oriented numerical studies have lent support to the idea, but the scope of their results is limited by the two-dimensional nature of the flows considered and by the simple model used to account for the behavior of plankton. In this paper, we relax both constraints. We solve the three-dimensional Navier-Stokes equation to compute the time dependent velocity field, and we use an empirically based model for the behavior of plankton. Our results show that accumulation and transport is possible, even for larvae characterized by sustained swimming speeds that are small compared with the speed of propagation of the front. We introduce a simple model to characterize the accumulation along the front, which includes both entrainment and detrainment. The model accurately represents accumulation calculated from the numerical runs, and provide a simple tool to estimate transport under a variety of circumstances. We also investigate the spatial distribution of plankton along and across the front and show that it is very patchy and dependent on the swimming speed of plankton, with important implications for interpreting results from field experiments.
Existing atmospheric correction algorithms for multichannel remote sensing of ocean color from space were designed for retrieving water-leaving radiances in the visible over clear deep ocean areas and cannot easily be modified for retrievals over turbid coastal waters. We have developed an atmospheric correction algorithm for hyperspectral remote sensing of ocean color with the near-future Coastal Ocean Imaging Spectrometer. The algorithm uses look-up tables generated with a vector radiative transfer code. Aerosol parameters are determined by a spectrum-matching technique that uses channels located at wavelengths longer than 0.86 mum. The aerosol information is extracted back to the visible based on aerosol models during the retrieval of water-leaving radiances. Quite reasonable water-leaving radiances have been obtained when our algorithm was applied to process hyperspectral imaging data acquired with an airborne imaging spectrometer.
We present satellite imagery that is interpreted as showing extensive lines of floating Sargassum in the western Gulf of Mexico in the summer of 2005. In spite of frequent reports of floating weed covering extended areas in different parts of the world's ocean, this appears to be the first observation of Sargassum from space. Satellite observations were made with the Medium Resolution Imaging Spectrometer (MERIS) on the Envisat satellite launched by the European Space Agency, and subsequently with the Moderate Resolution Imaging Spectroradiometer (MODIS) launched on both the Terra and Aqua satellites by the National Aeronautics and Space Administration. Both instruments cover wide swaths, providing near-daily images. Both have optical spectral bands in the range 670 to 750 nm, which detect the chlorophyll red-edge characteristic of land and marine vegetation, but only MERIS has a band at 709 nm, which was critical to the initial discovery. The combined satellite data from both sensors show the seasonal cycle of weed density in different areas of the Gulf. A wider ranging study is now needed to map its occurrence in other areas, including the Sargasso Sea (named for the weed, but not so far covered in our survey). The satellite observations suggest that Sargassum biomass is greater than previously estimated, and hence plays a more important part in oceanic productivity
Data with 0.4-m spatial resolution acquired ~2 km off the southeast Florida coast using the airborne Portable Hyperspectral Imager for Low-Light Spectroscopy (PHILLS) have been analyzed with the objective of identifying drifting surface macroalgae (Sargassum) through its spectral signature in at-sensor radiance. The observed spectral features of Sargassum include a peak at a wavelength of ~0.570 mum and a photosynthetic 'red edge' between 0.673 and 0.699 mum. Sargassum also exhibits high radiance in the reflected near-infrared but is impacted by the atmospheric absorption bands of water vapor at 0.720 mum and oxygen at 0.756 mum. The spectral signature is clearest and largest in amplitude where the Sargassum occurs as small surface aggregations, or rafts, which tend to lie at the downwind ends of narrow Sargassum windrows. The quantity of floating Sargassum was estimated within a single pixel by linearly mixing a spectrum of Sargassum-free water with varying percentages of a spectrum from a pixel assumed completely filled with floating plants. For our study site about 2.3% of the ocean area is classified as having some Sargassum coverage, with pixels completely filled with Sargassum being rare (only 0.2% of the classified Sargassum pixels) and pixels with the least-resolvable amount of Sargassum (~10% filled) being the most common.
Airborne synthetic aperture radar and high-resolution infrared imagery are used to examine the evolution of natural ocean slicks during a period of freshening wind. Initially the slicks are of the order of 50 m in width and have radar and thermal contrasts of the order of 10 dB and several 0.1°C. While there can be over time a transient reorganization of surface film material by internal waves, the slicks are observed to disperse and are no longer detectible after 5 h. The dispersion occurs through the action of Langmuir circulation, which results in along-wind streaks or “windrows”, as well as other effects. Prominent streaks occur preferentially along a slick's upwind side, the downwind side resembling more of a “leading edge”, at least early on. Over time, the leading edge develops a corrugated shape, and gaps begin to develop within the slicks. The formation of gaps is compared with a conceptual model by Dysthe (2006) for the tearing of a surface film in the region of positive surface straining. Eventually, the slicks break into elongated patches that co-exist with windrows, which is consistent with the effects of advective dispersion.
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The long survival of the free-floating plant Sargassum in the wind-mixed surface waters of the oceans is poorly understood. Evidence is presented here that the amounts of Sargassum collected by net tows at the sea surface decrease with increased wind speed. From this new finding and additional evidence in the marine literature, it is hypothesized that the plant is adapted to a cyclic submergence in the wind-induced vortical currents of these waters, returning to the surface only when the currents are less than the plant's rise rate. Such adaptation, readily testable, indicates the plant's capacity to maintain its density and rise rate independent of depth, thus adding to our understanding of its survival at sea.
Chromophoric dissolved organic matter (CDOM) strongly absorbs solar radiation in the blue-green and serves as the primary attenuator of water column ultraviolet radiation (UV-R). CDOM interferes with remote sensing of ocean chlorophyll and can control UV-R-induced damage to light-sensitive organisms including corals. We used laboratory incubations to evaluate CDOM production from senescing Rhizophora mangle (red mangrove) leaf litter (yellow, orange, and brown) and floating Sargassum colonies. Mangroves exist at the land–ocean interface near coral reefs in sub-tropical and tropical regions while floating Sargassum colonies tend to congregate in sub-tropical ocean gyres. CDOM production (∼48h) from mangrove leaves collected during a dry period in June 2004 (0.17±0.11m−1g−1lh−1) was lower than production from leaves collected during a wet period in September 2003 (0.57±0.42m−1g−1lh−1) suggesting that CDOM production from leaf litter fluctuates in response to environmental factors. CDOM production was greatest for the mid-senescence orange leaves and lowest for the severely senesced brown leaves in both experiments. Along the sub-tropical Florida Keys coral reef ecosystem, the primary source of CDOM is discharge from the shallow seagrass-dominated Florida Bay as evidenced by a strong correlation between field CDOM measurements and previously reported Florida Bay discharge volumes. However, field observations provide evidence that large expanses of red mangroves throughout the Keys could be important CDOM sources to the region's coral reefs during periods of reduced Florida Bay discharge. Floating Sargassum colonies also readily produced CDOM in laboratory incubations, but at much more variable rates than mangrove leaves. However, our calculations indicate that large mats of floating Sargassum could provide important CDOM quantities to oligotrophic oceanic waters including the Gulf of Mexico and North Atlantic.
In this article we study the wave-induced drift of large, flexible shallow floating objects, referred to as sheets. When surface waves propagate through a sheet, they provide a mean stress on the sheet, resulting in a mean drift. In response, the sheet generates an Ekman current. The drift velocity of the sheet is determined by (i) the wave-induced stress, (ii) the viscous stress due to the Ekman current, and (iii) the Coriolis force. The sheet velocity and the current beneath the sheet are determined for constant and depth-varying eddy viscosities.
The small-scale structure of oceanic fronts contains important information about horizontal and vertical exchange of properties in the upper ocean. The data obtained in the western equatorial Pacific warm pool during Tropical Ocean – Global Atmosphere Coupled Ocean – Atmosphere Response Experiment (TOGA COARE) and Tropical Ocean Climate Study (TOCS) suggest that the sharp frontal interfaces occasionally observed in the upper layer of the tropical ocean may be associated with gravity currents. These gravity currents originate from the surface pools of relatively low-density (fresh and/or warm) water produced by convective rainfalls and spatially variable diurnal warming. It has been shown that frontal interfaces of less than 100 m width may interact with wind stress via the mechanism of Stommel's ''overturning gate.'' The anisotropy of sharp frontal interfaces with respect to the wind stress direction can be predicted with a simple nonlinear model including both dissipation and dispersion effects. This study elucidates the role of fronts in the dynamics of the tropical ocean and provides important details to the description of how the temperature – salinity relationship and barrier layer in the warm pool areas are formed. D 2002 Elsevier Science B.V. All rights reserved.
Rafting has been inferred as an important dispersal mechanism in the marine environ-ment by many authors. The success of rafting depends critically on the availability of suitable floating substrata. Herein currently available information on floating items that have been reported to carry rafting organisms is summarised. Floating items of biotic origin comprise macroalgae, seeds, wood, other vascular plants, and animal remains. Volcanic pumice (natural) and a diverse array of litter and tar lumps (anthropogenic) are the main floating items of abiotic origin. Macroal-gae, wood, and plastic macrolitter cover a wide range of sizes while pumice, microlitter, and tar lumps typically are <10 cm in diameter. The longevity of floating items at the sea surface depends on their origin and likelihood to be destroyed by secondary consumers (in increasing order): nonlignified vascular plants/animal carcasses < macroalgae < driftwood < tar lumps/skeletal remains < plastic litter < volcanic pumice. In general, abiotic substrata have a higher longevity than biotic substrata, but most abiotic items are of no or only limited food value for potential rafters. Macroalgae are most abundant at mid-latitudes of both hemispheres, driftwood is of major importance in northern and tropical waters, and floating seeds appear to be most common in tropical regions. Volcanic pumice can be found at all latitudes but has primarily been reported from the Pacific Ocean. Plastic litter and tar lumps are most abundant near the centres of human population and activities. In some regions of abundant supply or zones of hydrography-driven accumulation, floating items can be extremely abundant, exceeding 1000 items km –2 . Temporal supply of floating items is variable, being seasonal for most biotic substrata and highly sporadic for some items such as volcanic pumice. Most reported velocities of floating items are in the range of 0.5–1.0 km h –1 , but direct measurements have shown that they occasionally are transported at much faster velocities. Published trajectories of floating items also coincide with the main oceanic currents, even though strong winds may sometimes push them out of the principal current systems. Many studies hint toward floating items to link source regions with coastal sinks, in some cases across long distances and even entire ocean basins. Fossil evidence suggests that rafting has also occurred in palaeo-oceans. During recent centuries and decades the composition and abundance of floating items in the world's oceans have been strongly affected by human activities, in particular logging, river and coastline regulation, and most importantly oil exploitation and plastic production. The currently abundant supply and the characteristics of floating items suggest that rafting continues to be an important dispersal mechanism in present-day oceans.
Vagile large juvenile and adult fishes are often under-represented in traditional sampling of Sargassum–associated fishes in the open ocean. We used underwater video recordings from free-floating camcorders and a remotely operated vehicle (ROV) to assess the relative abundance of large mobile fishes under large Sargassum mats (> 10 m diameter), under dispersed clumps of Sargassum (< 1="" m="" diameter),="" and="" in="" open="" water="" without="" sargassum="" as="" a="" reference.="" in="" addition,="" we="" conducted="" dipnet="" sampling="" in="" each="" sargassum="" treatment="" for="" a="" comparison="" to="" traditional="" methods.="" all="" samples="" were="" obtained="" in="" september="" 1992="" along="" the="" western="" wall="" of="" the="" gulf="" stream="" off="" cape="" hatteras,="" north="" carolina.="" a="" total="" of="" 31="" fish="" taxa="" were="" identified="" from="" both="" video="" and="" dipnet="" collections.="" only="" 8="" taxa="" were="" identified="" in="" both="" video="" and="" dipnet="" collections,="" while="" 11="" taxa="" were="" seen="" only="" in="" video="" and="" 10="" were="" only="" found="" in="" dipnet="" collections.="" dipnet="" collections="" were="" dominated="" by="" juvenile="" balistids="" and="" other="" small,="" cryptic="" fishes,="" while="" the="" video="" observations="" were="" mainly="" of="" larger,="" rapidly-moving="" carangids.="" fish="" diversity="" increased="" with="" the="" amount="" of="" continuous="" sargassum="" habitat:="" four="" taxa="" were="" observed="" when="" no="" sargassum="" was="" present,="" 12="" under="" clumps,="" and="" 19="" under="" mats.="" our="" results="" indicated="" that="" mat="" morphology="" significantly="" affects="" the="" sargassum–associated="" fishes,="" and="" that="" both="" video="" and="" traditional="" capture="" methods="" are="" complementary="" and="" should="" be="" used="" together="" to="" accurately="" census="" this="">
Various types of floating algae have been reported in open oceans and coastal waters, yet accurate and timely detection of these relatively small surface features using traditional satellite data and algorithms has been difficult or even impossible due to lack of spatial resolution, coverage, revisit frequency, or due to inherent algorithm limitations. Here, a simple ocean color index, namely the Floating Algae Index (FAI), is developed and used to detect floating algae in open ocean environments using the medium-resolution (250- and 500-m) data from operational MODIS (Moderate Resolution Imaging Spectroradiometer) instruments. FAI is defined as the difference between reflectance at 859 nm (vegetation “red edge”) and a linear baseline between the red band (645 nm) and short-wave infrared band (1240 or 1640 nm). Through data comparison and model simulations, FAI has shown advantages over the traditional NDVI (Normalized Difference Vegetation Index) or EVI (Enhanced Vegetation Index) because FAI is less sensitive to changes in environmental and observing conditions (aerosol type and thickness, solar/viewing geometry, and sun glint) and can “see” through thin clouds. The baseline subtraction method provides a simple yet effective means for atmospheric correction, through which floating algae can be easily recognized and delineated in various ocean waters, including the North Atlantic Ocean, Gulf of Mexico, Yellow Sea, and East China Sea. Because similar spectral bands are available on many existing and planned satellite sensors such as Landsat TM/ETM+ and VIIRS (Visible Infrared Imager/Radiometer Suite), the FAI concept is extendable to establish a long-term record of these ecologically important ocean plants.
The ability of high-resolution imaging systems to resolve small-scale structure on the ocean surface suggests the possibility of using characteristics of Langmuir circulation to map the surface mixed-layer depth and near-surface current. We illustrate this using synthetic aperture radar and infrared imagery that are collected across the edge of the Gulf Stream (GS), which reveals surfactant streaks, or ldquowindrows,rdquo that are induced by Langmuir circulation. Based on changes in the windrow spacing and orientation, the mixed layer is estimated to deepen from 7 to 12 m across the edge of the GS and the current to increase from about 1 to 2 m/s. These spatial changes compare reasonably well with independent data, suggesting that the approach is plausible. It may also be possible to extract additional environmental information from the windrows.
The presence of phytoplankton in a body of water a#ects the penetration of irradiance through the water column. This influences the temperature and hence the density distribution of the water. If the phytoplankton concentration varies horizontally, then the consequent density distribution will result in a horizontal pressure gradient. Here we consider a long band (or strip) of high phytoplankton biomass, flanked on either side by clearer water containing little biomass. By means of a simple model we present calculations of the velocities induced by the pressure gradients, to show under what conditions the di#erential heating e#ects may become significant. The model's momentum equations assume a steady state, and include e#ects of Coriolis and vertical eddy viscosity. An analytical solution is obtained, and the induced velocities are shown graphically. Further calculations investigate the potential for the biologically-induced vertical velocities to transport nutrients into the surface waters and subsequently influence new primary production. This work demonstrates the capacity for feedbacks from the biological component of the ecosystem to the physical component (and back again).
Marine neustonology (translated from Russian) Israel Program for Scientific Translations, Jerusalem. 207pp. Available from the U.S. Department of Commerce, National Technical Information Service
- Y P Zaitsev
Zaitsev, Y.P., 1971. Marine neustonology (translated from Russian). Israel Program for Scientific Translations, Jerusalem. 207pp. Available from the U.S. Department of Commerce, National Technical Information Service, Springfield, VA 22151, and also online at /http://www.ceemar.org/dspace/handle/11099/132S. G.O. Marmorino et al. / Deep-Sea Research I 58 (2011) 316–321