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Assessment of benthic habitats of highly threatened oyster reefs of Pulicat Lake, India
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By filtering large volumes of water and releasing nutrient-rich biodeposits (feces and pseudofeces), oysters can locally enhance sediment biogeochemical cycling. An active Crassostrea virginica restoration program in Mosquito Lagoon, FL (USA), was leveraged to assess the immediate (first-year) effects of restoration on sediment nutrients. Measurements included extractable and total carbon, nitrogen, and phosphorus on dead, natural, and restored reefs using a before-after-control-impact design. To investigate an observed "age-nutrient paradox" in sediment nutrient concentrations, a laboratory experiment compared feeding rates and biodeposit nutrient content between juvenile and older oysters. The field study documented a 136% increase in ammonium, 78% increase in total nitrogen, 46% increase in total phosphorus, and 75% increase in organic matter concentrations 12 months post-restoration, with extractable nutrients responding more rapidly to restoration than total nutrients. Sediment nutrient increases were positively correlated with oyster density, shell length, and reef height. Moreover, the laboratory study indicated juvenile oysters had higher rates of chlorophyll-a removal and ammonium efflux and produced biodeposits with higher concentrations of dissolved organic carbon, nitrate, and ammonium than older oysters. Overall, this study documented increases in sediment nutrients on intertidal reefs within the first year of restoration, which may be explained by a greater filtration rate and more nutrient-enriched biodeposits contributed by young oysters as compared to older oysters. Sediment total nitrogen and ammonium content may be the most robust monitoring metrics for documenting the ecosystem service of enhanced biogeochemical cycling on restored oyster reefs.
Over 85% of the world's oyster reefs have been lost in the past two centuries, triggering a global effort to restore shellfish reef ecosystems and the ecosystem services they provide. While there has been considerable success in re-establishing oyster reefs, many challenges remain. These include: high incidence of failed restoration, high cost of restoration per unit area, and increasing stress from climate change. In order to leverage our past successes and progress the field, we must increase restoration efficiencies that not only reduce cost per unit area, but also increase the resilience of restored ecosystems. To help address this need, we qualitatively review the literature associated with the structure and function of oyster reef ecosystems to identify key positive species interactions (i.e., those species interactions where at least one partner benefits and no partners are harmed). We classified positive inter- and intraspecific interactions between oysters and organisms associated with oyster ecosystems into the following seven functional categories: (1) physical reef creation, (2) positive density dependence, (3) refugia from physical stress, (4) refugia from biological stress, (5) biodiversity enhancement, (6) settlement improvement, and (7) long-distance facilitation. We discuss each category of positive interaction and how restoration practitioners can use knowledge of such processes to enhance restoration success. We propose that systematic incorporation of positive species interactions into restoration practice will both enhance ecological services provided by restored reefs and increase restoration success.
Grazing interaction between gastropods and seaweeds eventually form a key component of intensified grazing ecosystem in rocky intertidal area. Grazing gastropods suppresses the abundance of canopy forming algal species, thus lead to a reduced algal diversity in the long term. We conducted feeding trials with single and mixed diet during a 28-Days indoor experiment to examine the grazing intensity among green, red and brown algae namely Ulva lactuta, Enteromorpha flexuosa and Sargassum cinerium following a comparative analysis of gut content of both Euchelus sp. and Nerita sp. show the occurrence of semidigested seaweed diet in their gut. About 70% of Euchelus sp. consumes Enteromorpha sp. 40% feeds on Ulva and 20% on Sargassum sp. whereas about 13% Nerita sp. consumes Ulva sp. and Enteromorpha sp. equally during the study period. Maximum numbers of Euchelus sp. are recorded with semidigested seaweed feed in gut compared to Nerita sp. Nonselective feeding habit of Euchelus sp. may pose a threat to nature in terms of reduction of biodiversity and ecological balance. This pioneer work on intertidal grazing relationship in India may help in deciding the feeding strategy in molluscan culture and taking some preventive measure in seaweed culture.
Oyster reefs have the potential as eco-engineers to improve coastal protection. A field experiment was undertaken to assess the benefit of oyster breakwater reefs to mitigate shoreline erosion in a monsoon-dominated subtropical system. Three breakwater reefs with recruited oysters were deployed on an eroding intertidal mudflat at Kutubdia Island, the southeast Bangladesh coast. Data were collected on wave dissipation by the reef structures, changes in shoreline profile, erosion-accretion patterns, and lateral saltmarsh movement and related growth. This was done over four seasons, including the rainy monsoon period. The observed wave heights in the study area ranged 0.1–0.5 m. The reefs were able to dissipate wave energy and act as breakwaters for tidal water levels between 0.5–1.0 m. Waves were totally blocked by the vertical relief of the reefs at water levels <0.5 m. On the lee side of the reefs, there was accretion of 29 cm clayey sediments with erosion reduction of 54% as compared to control sites. The changes caused by the deployed reefs also facilitated seaward expansion of the salt marsh. This study showed that breakwater oyster reefs can reduce erosion, trap suspended sediment, and support seaward saltmarsh expansion demonstrating the potential as a nature-based solution for protecting the subtropical coastlines.
Eastern oysters (Crassostrea virginica) are ecosystem engineers that are important to the ecological and economic sustainability of Atlantic Canada's estuarine resources. Recently, there has been an increased industry demand for oyster spat (i.e., newly-settled larvae), which is often collected using artificial spat collectors suspended in the water column. Little is known, however, about the interactions between artificial spat collectors and naturally occurring substrates, and whether or not such collectors can affect oyster recruitment to wild beds which are simultaneously fished. In the laboratory, we mimicked the typical setup of artificial spat collectors used in Atlantic Canada to measure differences in spat recruitment between locally-used artificial collectors and natural shell substrate under real-life spat-collection scenarios. Larvae were allowed to settle on various sub-strates where they occur in a natural system and were subsequently counted. In both single substrate and choice experiments, results indicated that oyster larvae recruited in higher numbers to natural shell substrate located on the benthic surface compared to suspended shell; and there were no significant differences among suspended substrates. This experiment provides evidence supporting existing theories around recruitment behaviour by oyster larvae, mainly that settling oysters tend to sink before they settle, suggesting that spat collectors in the wild may have little effect on wild recruitment. With increasing densities of artificial collectors in estuarine systems to meet system demands, however, further research is needed to investigate the potential draw of oyster larvae away from benthic oyster beds under more realistic natural conditions before broad conclusions regarding spat collector effects on wild oyster populations can be achieved.
Marine ecosystems of temperate regions are highly modified by human activity and far from their original natural status. The North Sea, known as an intensively used area, has lost its offshore oyster grounds due to overexploitation in a relatively short time. Native oyster beds as a once abundant and ecologically highly important biogenic reef-type have vanished from the North Sea ecosystem in most areas of both their former distribution and magnitude. Worldwide, oyster stocks have been severely exploited over the past centuries. According to estimates, about 85% of the worldwide oyster reef habitats have been destroyed over the course of the last century. This loss of oyster populations has meant far more than just the loss of a valuable food resource. Oyster reefs represent a characteristic benthic community which offers a variety of valuable ecosystem services: better water quality, local decrease of toxic algal blooms, increase in nutrient uptake, increase of bentho-pelagic coupling, increase in species richness, increase of multidimensional biogenic structures which provide habitat, food, and protection for numerous invertebrate and fish species. The aim of oyster restoration is to promote redevelopment of this valuable missing habitat. The development of strategies, methods, and procedures for a sustainable restoration of the European oyster Ostrea edulis in the German North Sea is currently a focus of marine nature conservation. Main drivers for restoring this ecological key species are the enhancement of biodiversity and ecosystem services in the marine environment. Results of these investigations will support the future development and implementation of a large-scale and long-term German native oyster restoration programme to re-establish a healthy population of this once-abundant species now absent from the region.
Spat density was found to be higher in asbestos sheet with a mean value of 6.36 spats/ 100 cm 2. Environmental parameters such as salinity, temperature, DO, and pH were recorded in response to inter-seasonal variability, varied significantly (P<0.05) between seasons. Dissolved oxygen levels varied from 3.9 mg/L to 5.533 mg/L, and no significant difference was observed for DO levels between these seasons. The pH was significantly lowered (P<0.05; F = 69.25) during pre-monsoon and monsoon. Growth rate was rapid during the month of May (22±1.5 mm month-1) to June (18.5±0.79 mm month-1) due to freshwater influx from the upper reaches of the estuaries causes heavy precipitation in the catchment areas of the rivers and in October (18±1.02 mm month-1) due to northeast monsoon rains.
Haematological parameters are valuable indicators of fish health status. This study is aimed to provide baseline data of the blood profile of two teleost fish species living in different environments and with divergent feeding behaviour, namely the flathead grey mullet Mugil cephalus Linnaeus, 1758, a marine herbivorous fish, and the goldfish Carassius auratus (Linnaeus, 1758), a freshwater omnivorous fish. Using an automated system coupled with flow cytometry and light microscopy, significant variations were found between M. cephalus and C. auratus blood parameters, except for haemoglobin concentration (Hgb). A significant increase in red blood cell count (RBC) and haematocrit (Hct) levels, associated with reduced mean corpuscular volume (MCV), was revealed in mullets in respect to goldfish. These data may be attributable to differences in fish species, or to their divergent physiological activeness as high RBC values are associated with fast movement and high activity with streamlined bodies, or to environmental factors such as water salinity, an increase in which may lead to erythropoiesis as an adaptive process in seawater fish. Additionally, lower values of white blood cell count (WBC) and thrombocyte count (TC) were recorded in mullets with respect to goldfish, and these changes may be due to divergent feeding habits of the two fish species, or to their different environments since increased salinity may inversely affect WBC. Overall, findings from this study provide a better understanding of the influences of divergent environmental conditions and feeding habits on fish blood parameters. The combined use of an automatic haematological count with flow cytometry was demonstrated to be effective for an early assessment of blood parameters in different fish species.
A wide variety of organisms are known to graze on seagrasses and their associated epiphytes, and this plant-animal interaction can affect the health of seagrass meadows. Grazing patterns tend to vary across meadows and faunal groups, and little is known regarding how gastropod grazers influence meadows in the tropics. To better understand this interaction, we surveyed the gastropod diversity in five meadows in Singapore. Further, grazing potential (i.e. potential food sources and feeding rates) of common gastropod species was quantified through ex situ grazing experiments, while their diet compositions were elucidated using dual δ ¹³ C and δ ¹⁵ N stable isotope analyses. The surveys revealed a high diversity of 274 gastropod species/morphospecies while PERMANOVA and SIMPER analyses showed that communities differed significantly among sites but not among seagrass species. Diet composition analysis indicated that seagrass leaves were the main food source for most gastropod species examined while epiphytes were important for microsnail (shell size <5 mm) species. However, all the gastropod species tested fed on epiphytes in the ex situ experiments. These findings contribute new insights into grazing by marine gastropods on tropical seagrass meadows, and highlight the potential importance of both direct grazing and epiphyte removal on tropical meadows.
We review the status of marine shellfish ecosystems formed primarily by bivalves in Australia, including: identifying ecosystem-forming species, assessing their historical and current extent, causes for decline and past and present management. Fourteen species of bivalves were identified as developing complex, three-dimensional reef or bed ecosystems in intertidal and subtidal areas across tropical, subtropical and temperate Australia. A dramatic decline in the extent and condition of Australia’s two most common shellfish ecosystems, developed by Saccostrea glomerata and Ostrea angasi oysters, occurred during the mid-1800s to early 1900s in concurrence with extensive harvesting for food and lime production, ecosystem modification, disease outbreaks and a decline in water quality. Out of 118 historical locations containing O. angasi-developed ecosystems, only one location still contains the ecosystem whilst only six locations are known to still contain S. glomerata-developed ecosystems out of 60 historical locations. Ecosystems developed by the introduced oyster Crasostrea gigas are likely to be increasing in extent, whilst data on the remaining 11 ecosystem-forming species are limited, preventing a detailed assessment of their current ecosystem-forming status. Our analysis identifies that current knowledge on extent, physical characteristics, biodiversity and ecosystem services of Australian shellfish ecosystems is extremely limited. Despite the limited information on shellfish ecosystems, a number of restoration projects have recently been initiated across Australia and we propose a number of existing government policies and conservation mechanisms, if enacted, would readily serve to support the future conservation and recovery of Australia’s shellfish ecosystems.
During our routine ecological survey conducted at Pulicat Lagoon, the most diverse class Gastropods comprised of 26 families with 34 species and Bivalvia with 13 families and 17 species were recorded. The most abundant molluscs species was Crassostrea madrasensis, captured between October 2013 − September 2015. Quite a good number of molluscs were washed ashore. The economic value of the shells in the field of cosmetics was raised high recently. Both in terms of aquaculture and market value the attention should be diverted towards their conservation. With few exceptions, the majority of these molluscs were ornamental.
The presence, abundance, and distribution of organisms within a landscape are highly dependent on the composition, quality, and configuration of habitat patches. Intertidal oyster Crassostrea virginica reefs provide a structured habitat for many organisms; however, declining oyster populations have induced reef fragmentation and loss. Over 2 years (2011-2012), we evaluated naturally occurring fringing and patch intertidal oyster reefs in southeastern North Carolina, USA, to determine how varied reef type, size, and distance from edge to interior influenced the associated benthic macrofauna and mobile nekton. In addition, the effects of size and edge vs. interior were examined on constructed intertidal reefs at 2 different locations. On the natural reefs, species richness of benthic macrofauna and mobile nekton were significantly increased on fringing reefs. Benthic macrofauna richness significantly decreased on large natural reefs, whereas mobile nekton richness significantly increased off of large reefs. Further, associated ben-thic macrofauna richness significantly decreased along the reef edge, whereas mobile nekton diversity increased along the reef/open bottom interface. Species richness and densities for ben-thic macrofauna increased with created reef size, while there was greater species richness and diversity and dissimilar communities for mobile nekton along constructed reef edges. Habitat specificity may influence utilization for mobile nekton, as resident organisms with limited vagility had a stronger response to habitat characteristics. Thus, utilization of intertidal oyster reefs can be highly structured by habitat characteristics on many scales, and should be considered when examining species interactions, ecosystem management, and future restoration efforts.
Carbon burial is increasingly valued as a service provided by threatened vegetated coastal habitats. Similarly, shellfish reefs contain significant pools of carbon and are globally endangered, yet considerable uncertainty remains regarding shellfish reefs' role as sources (+) or sinks (-) of atmospheric CO2 While CO2 release is a by-product of carbonate shell production (then burial), shellfish also facilitate atmospheric-CO2 drawdown via filtration and rapid biodeposition of carbon-fixing primary producers. We provide a framework to account for the dual burial of inorganic and organic carbon, and demonstrate that decade-old experimental reefs on intertidal sandflats were net sources of CO2 (7.1 ± 1.2 MgC ha-1 yr-1 (µ ± s.e.)) resulting from predominantly carbonate deposition, whereas shallow subtidal reefs (-1.0 ± 0.4 MgC ha-1 yr-1) and saltmarsh-fringing reefs (-1.3 ± 0.4 MgC ha-1 yr-1) were dominated by organic-carbon-rich sediments and functioned as net carbon sinks (on par with vegetated coastal habitats). These landscape-level differences reflect gradients in shellfish growth, survivorship and shell bioerosion. Notably, down-core carbon concentrations in 100- to 4000-year-old reefs mirrored experimental-reef data, suggesting our results are relevant over centennial to millennial scales, although we note that these natural reefs appeared to function as slight carbon sources (0.5 ± 0.3 MgC ha-1 yr-1). Globally, the historical mining of the top metre of shellfish reefs may have reintroduced more than 400 000 000 Mg of organic carbon into estuaries. Importantly, reef formation and destruction do not have reciprocal, counterbalancing impacts on atmospheric CO2 since excavated organic material may be remineralized while shell may experience continued preservation through reburial. Thus, protection of existing reefs could be considered as one component of climate mitigation programmes focused on the coastal zone.
Turritella duplicata (Linnaeus, 1758) is a marine suspension-feeding gastropod found in shallow-marine and tidal flat environments throughout Southeast Asia and the Indo-West Pacific. It was studied on a tidal flat in the national park of Nopparat Thara in the district of Krabi, southern Thailand. Turritella duplicata was found primarily in the lower intertidal zone, and 90 specimens were gathered and measured. Their geographical positions on the flat were mapped, revealing zonations in population distribution, both parallel and perpendicular to the shore-line. The size distribution of the shells indicates that the population consists exclusively of adults. δ¹⁸O sclerochronology performed on three shells shows variations of up to 1.5‰ associated with seasonal changes in water parameters, suggesting longevity of about three years and seasonally controlled growth rates. The absence of juveniles and observed population distribution coupled with the sclerochronological data suggest that reproduction occurs in early spring, and that the population represents three cohorts approximately one year in age and older. Migration to deeper water during other seasons cannot be ruled out. Smaller individuals were preferentially found on the inner tidal flat, and individuals older than two years preferentially colonised the outer tidal flat. The carbon isotopic composition of the analysed shells partially tracks these life stages, suggesting that metabolic "vital effects" are influencing the δ¹³C of the shells.
Oyster reefs are important components of marine ecosystems and function as essential habitat for estuarine species; however, few studies have simultaneously compared natural intertidal reefs to more well-studied seagrass meadows and marsh habitats. We investigated habitat use within an estuarine mosaic consisting of intertidal oyster reef (Crassostrea virginica), seagrass (Halodule wrightii), and marsh edge (Spartina alterniflora) habitats in Corpus Christi Bay, Texas. Oyster sampling units (OSUs) were deployed within intertidal oyster reef, and modified throw traps were used to collect macrofauna inhabiting the OSU and other adjacent vegetated habitats. Habitat arrangement and proximity as it relates to macrofaunal density, species richness, and community composition were also evaluated by comparing communities in oyster reef within the oyster reef complex, oyster reef adjacent to a seagrass complex, and oyster reef adjacent to marsh edge. Higher macrofaunal densities and species richness were observed within oyster reefs compared to seagrass and marsh edge. Oyster reef also supported a distinct community, while seagrass and marsh shared similar species composition and richness. The highest densities of macrofauna were collected on oyster reefs near seagrass and oyster reef located within the oyster reef complex. These results indicate the importance of intertidal oyster reefs to macrofauna and that reef location within the estuarine mosaic influences density and community assemblages. These findings are important because in many areas there are large efforts to restore oyster reef in estuarine systems, and for these programs to be successful, it is necessary to understand the functional roles and linkages among habitats.
The Pulicat Lake avifauna, aquatic and mudflat faunal diversity were described. During the years 2007-2009 about 31 bird species visited Pulicat Lake feeding grounds. During monsoon season about 75-85% of zooplankton belong to copepoda and decapoda. Due to tectonic upliftment of lake bed West of Rayadoruvu sea mouth, Attakanithippa and Weynadu areas a shallow water regime persists. This is responsible for rich biodiversity namely crustacean plankton, juvenile shrimps and migratory fishes from sea to lake and vice versa acting as food for Pelicans, Flamingoes and a variety of waders unlike near Pulicat Village south end sea mouth due to deep water regime. It is opined that the avifaunal and aquatic faunal diversity and density depends upon Pulicat Lake water level and water resident time. This is in turn dependent on sea mouth width and monsoon rainfall amounts. Loss of avifaunal and aquatic faunal diversity were attributed to quick drying up of lake in January due to less flow of sea water from constricted sea mouths even before the migratory bird season which lasts up to March. A few important fishes and shrimps which migrate from sea to lake and vice versa were described. The causes of ecodegradation is discussed.
Within intertidal communities, aerial exposure (emergence during the tidal cycle) generates strong vertical zonation patterns with distinct growth boundaries regulated by physiological and external stressors. Forecasted accelerations in sea-level rise (SLR) will shift the position of these critical boundaries in ways we cannot yet fully predict, but landward migration will be impaired by coastal development, amplifying the importance of foundation speciesa ability to maintain their position relative to rising sea levels via vertical growth. Here we show the effects of emergence on vertical oyster-reef growth by determining the conditions at which intertidal reefs thrive and the sharp boundaries where reefs fail, which shift with changes in sea level. We found that oyster reef growth is unimodal relative to emergence, with greatest growth rates occurring between 20-40% exposure, and zero-growth boundaries at 10% and 55% exposures. Notably, along the lower growth boundary (10%), increased rates of SLR would outpace reef accretion, thereby reducing the depth range of substrate suitable for reef maintenance and formation, and exacerbating habitat loss along developed shorelines. Our results identify where, within intertidal areas, constructed or natural oyster reefs will persist and function best as green infrastructure to enhance coastal resiliency under conditions of accelerating SLR.
Pulicat lagoon is the semi enclosed and second largest brackish water body in tropical India. The morphology, water quality and biological productivity of the lagoon had being subjected to noteworthy changes over the years under the influence of natural as well as human interference. Recent research have revealed that the lagoon losses its biological integrity due to more sedimentation from rivers predominantly in monsoon seasons, lagoon mouth closure, overfishing, pollution from various phenomena such as usage of motor boats, sewage disposal and aquaculture farms. In this work, evaluation of the status of this lagoon in terms of its biological, physical and chemical importance, its flourishing inheritance, the threats to this ecosystem and the knowledge gaps with the recommendations towards protection of its declining biodiversity are discussed.
Fluctuations in salinity are known to influence coastal marine communities. In this study, we present the effect of salinity on the distribution characteristics of mesozooplankton in Pulicat lake, the second largest lagoon situated along the south east coast of India. During different seasons of the study period, salinity varied from hyposaline (12.57) to hypersaline (139.74) in the lake. Salinity values were moderate in southern (33.75 ± 0.7) and northern inlets (29.38 ± 4.33), which were connected with the sea; while in the central region of the lake salinity was observed to be higher (52.32 ± 4.57). Mesozooplankton biovolume and abundance were high in the southern and northern inlets whereas a severe reduction in diversity and abundance was observed in the central region of the lake manifesting that increase in salinity is negatively impacting the mesozooplankton distribution. Copepod (Acartia tonsa, Acrocalanus gibber, Paracalanus parvus, Oithona brevicornis and Oithona similis), crustacean and molluscan larvae dominated the mesozooplankton abundance. A. tonsa predominance (79%) over the lake and across different seasons indicates its tolerance to wide range of salinity fluctuations i.e., brackish to hypersaline environment of the Pulicat. The distribution of euryhaline species A. tonsa in all the sampling locations throughout the study period indicated their prevalence in the lake. Multilinear analysis between biotic and abiotic components through redundancy analysis (RDA) also suggested that salinity is the major constraint factor for the distribution of mesozooplankton. In conclusion, this study showed that the increased salinity levels have profound effects on mesozooplankton community and distribution.
Polychaetes were studied to assess the effect of aquaculture activity on the seafloor. Very high biodiversity of species was recorded associated with aquaculture centres with Cirratulidae, Spionidae and Paraonidae families being the most diverse and abundant families. The spatial distribution of polychaete trophic groups was the best descriptor for detecting changes on the benthos. Surface and subsurface deposit-feeding species dominated the sites closest to the rafts cages, highlighting Capitella capitata and Cirratulus cirratus as opportunistic species. While replacement and species succession were observed with increasing presence of carnivores and omnivores in sites further away from the salmon cages and experiencing less impact. Analyses based on the distance of feeding modes and ecological groups from the disturbance source were better indicators of the impact that the traditional community approach or sediment biogeochemistry. Therefore, functional traits studies should always be considered on environmental assessments of benthic systems impacted by aquaculture.
Globally, momentum to restore damaged habitats has been increasing. For example, the number of European shellfish restoration projects has quadrupled in the
past 3 years. In line with the increasing focus on both restoration and climate
change mitigation efforts, this study highlights how these two practices can complement each other.
2. This experimental study quantifies the active and passive sediment deposition
associated with the European flat oyster (Ostrea edulis) and the organic and inorganic carbon fractions of the deposits. Treatments included ‘dead’, ‘live’, and control to account for (i) passive deposition, (ii) biodeposition and passive deposition,
and (iii) background deposition respectively. By utilizing these data, the expected
carbon deposition associated with a restored flat oyster bed was investigated.
3. The experiment was conducted ex situ, with natural seawater input. Covariate
data on temperature, suspended particulate influx, salinity, and oxygen availability
were recorded. Enhanced sedimentation (2.9 times) and organic carbon deposition
(three times) were observed in the presence of living oysters, compared with the
control. The shell structure of the oysters had no influence on passive sedimentation in this study.
4. By developing a full understanding of the ecosystem services (functioning,
supporting, regulating, and cultural) provided by a habitat, it becomes possible to
quantify overall ecosystem function. This evidence is key in advising policymakers,
restoration funders, and marine spatial planners on the connection between keystone species restoration, ecosystem service restoration, and conservation
management.
5. The enhancement of benthopelagic coupling by the European flat oyster, evidenced
here for the first time, is contextualized from the perspective of quantification of
ecosystem service provision for both restoration practices and blue carbon store
management. The data produced in this study are discussed comparatively with
work that has focused on other species from both Europe and the USA.
The present study investigated the biodiversity of sessile and motile organisms using intertidal reef habitats constructed by giant oysters Magallana cuttackensis (Newton & Smith, 1912) and backwater oysters Magallana bilineata (Röding, 1798) at the Hab River Delta in Pakistan. A one year (February 2017 to January 2018) field survey was carried out to investigate the species diversity and abundance on the reefs and surrounding area. Monthly samples were taken and the abundance of macro-organisms was observed. Oysters were brought to the laboratory for a detailed examination of shells for the presence of other species. Specimens of 122 species were collected, including 35 new records for Pakistan. The most abundant phylum was Mollusca, represented by 55 species. Overall biodiversity was highest in the pre-monsoon season, declining in monsoon and post-monsoon periods. April was the month with the highest number of species observed. This study constitutes a baseline and an important step to gain a better understanding of oyster reefs and their ecological value as habitat for other species.
Reef building oysters historically provided the main structural and ecological component of temperate and sub‐tropical coastal waters globally. While the loss of oyster reefs is documented in most regions globally, assessments of the status of Asian oyster reefs are limited. The feasibility of restoration within the regional biological and societal contexts needs to be assessed before implementation. Here, we quantified the current distribution of natural oyster reefs (Crassostrea spp.) in the shallow coastal waters of Hong Kong, assessed the biological feasibility of re‐establishing reefs using natural recruitment, and examined their current and potential water filtration capacity as a key ecosystem service provided by restoration. We found natural low relief oyster beds in the low intertidal coastal areas at a subset of the locations surveyed. These areas are, however, degraded and have sparse densities of oysters generally <2 years old. Recruitment was high in some areas (>500,000 indiv. m⁻²) and while survival to maturity varied across sites there was adequate larval supply and survival for restoration. Filtration rates for a one‐year old recruit (90 mm length, ~30 L hr.⁻¹ per individual) at summer temperatures (30°C) meant that even the small remnant populations are able to provide some filtration services (up to 31.7 ML h⁻¹). High natural recruitment means that oyster reef restoration can be achieved with the addition of hard substrate for recruitment, increased protection of restoration sites, and would not only increase the ecological value of reefs regionally but also serve as a model for future restoration in Asia.
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Methodological choices made when studying functional feeding groups (FFGs) may influence the outcome of feeding diversity analyses and of the ecological quality assessment. We assessed the impact of select methodological choices based on seasonal macrobenthos surveys carried out in Bohai Bay, China. Results of the paired-sample t test showed that the choice to remove rare species from analyses had influence on the outcome of ecosystem evaluations based on FFG diversity (t = 2.328, p = 0.023). On the other hand, although results at some stations indicated that the removal of rare species did not affect feeding diversity and ecological assessment, it increased the research effort. Evenness feeding diversity calculated from FFG biomass data showed a remarkably different spatio-temporal distribution from that of values based on abundance data, with no clear relationship between the two. If biomass data are used to estimate FFG diversity, a revised ecological assessment scale may need to be developed.
This study aims to address the potential effects of environmental factors, competition and predation among cohabiting macrobenthos, and in particular on the cultured blood cockles (Tegillarca granosa). Macrobenthos and environmental variables were sampled from culture beds close to the harvesting period at two sites (BNO, BSB) in Selangor and one (KSB) in Perak (Malaysia). A total of 79 taxa were recorded mostly belonging to three taxonomic groups, Mollusca (27 taxa), Crustacea (26) and Actinopterygii (18). Redundancy analysis revealed close associations among the common scavenging/grazing gastropods (Nassarius bellulus and N. jacksonianus), predatory gastropods (Notocochlis tigrina and Indothais malayensis) and various macrobenthic species suggesting competition and predation risk to the cultured bivalves. The biomass of sediment chlorophyll-a (highest at BNO) was correlated with higher T. granosa and macrobenthic density. The higher ammonia level at BSB and KSB may explain the lower macrobenthic density and reduced competition allowing the venerid bivalve, Pelecyora cf. gouldii to proliferate at the expense of T. granosa. This study identified two abiotic factors (nutrient enrichment, ammonia) and two biotic factors (food limitation and predation) that potentially affect the production of densely-stocked T. granosa on the mudflat.
Eggs of Marphysa gravelyi are spawned in gelatinous masses and the developing larvae are harboured in them until they are ready to undergo settlement. In order to understand the function of the jelly mass, morphometric, histochemical, biochemical and antimicrobial analyses were performed. The observations indicate the fibrous jelly mass is composed of carbohydrate, protein and lipid, and size is correlated to number of eggs present within. Extracts from the jelly mass of Marphysa gravelyi exhibit inhibitory activity against Escherichia coli, Vibrio vulnificus and Candida albicans but no activity was seen against seven other microorganisms tested. The results show that the function of the jelly mass is to nourish the developing embryos, protect against desiccation and predation from macrofauna, and most importantly prevent the dispersal of the juveniles from the desirable habitat.
Horse mussel (Modiolus modiolus) shellfish reefs are a threatened and declining habitat in the North East Atlantic and support high levels of biodiversity. Shellfish can influence the surrounding water column and modify the quality of material that reaches the seabed by filtering water, actively depositing particles and changing the benthic boundary layer due to surface roughness. In the present study M. modiolus biodeposition was measured in a field location for the first time. The results show that M. modiolus enhance sedimentation and contribute to the downward flux of material to the seabed. Approximately 30% of the total sediment deposition was attributed to active filter feeding and overall, the presence of horse mussels enhanced deposition two fold. The results are discussed in terms of the potential for horse mussel reefs to provide ecosystem services to society, through functions such as benthopelagic coupling and sediment stabilisation. Highlighting the societal benefits supplied by marine habitats can help prioritise conservation efforts and feed into the sustainable management of coastal water bodies.
The present chapter provides a brief review of the main impacts on coastal marine ecosystems resulting from fisheries and aquaculture activities. It covers a wide range of topics, including habitat degradation, fragmentation, and loss; changes in biodiversity, food webs, and trophic interactions; loss of genetic diversity; and spread of parasites and diseases. A number of worldwide case studies on mitigation measures are presented, providing examples of best practices aiming to reduce impacts on coastal marine environments. Several restoration initiatives are also described based on selected case studies. Finally, the importance of restoration methods, as ecohydrology, based on a holistic approach to manage ecosystems and revert degradation, is highlighted.
Studies on the distribution and abundance of edible oysters from Chendia to Mejali along the Karwar coast in 1984 have shown that the resources conDprising of Saccostrea cucullata and Crassostrea madrasensis, predominantly the former, were present in sheltered regions namely the Chendia creek and Kailnadi estuary, but ware absent in the intertidal zone along the coast. The distribution of these species in the Kaiinadi estuary was isolated in patches from Sadashivgad upstream to Hotegali while it was scattered in the entire Chendia creek area. The exploitation of oyster in both the places was poor during the period of study. this 1. to 5 (Fig. 1). Of the five oyster beds, the region by Patil (1592), Alagarswami and first one, along the northern bank from Sadashi-Narasimham (1973) and Nair et al (1984) are based on surveys particularly of the Kaiinadi. Information hitherto published on the distribut-ion and abundance of edible oysters of this area is meagre.
An examination of oyster bed associated macrofauna provide a information for assessing the ecological quality of the substratum, oyster patch reef associated fauna and species inference on polychaetes assemblage of Vellar estuary. A total of 448 individuals samples were found, Polychaetes and crustacean were the most dominant groups, the diversity was highlight the species abundance, among this group the percentage composition was ranged between plot I 4.46–38.2 % followed by plot II 42.5–6.14 %, whereas in plot III 42.56–6.66 %. The environmental parameters are significantly correlated with these two species (p > 0.01), correlation parameter was indicate the level of macrofaunal assemblage with support of the environmental parameters, consequently of this studies to revealed the availability of the oyster population and diversity patterns of the cryptic organisms will assist easily to particular environment, these abundance of Vellar estuary the faced various problems such as sedimentation, siltation, shrinking aqua farms and domestic waste and some of the anthropogenic pressure.
In the high-salinity seaward portions of estuaries, oysters seek refuge from predation, competition and disease in intertidal areas1,2, but this sanctuary will be lost if vertical reef accretion cannot keep pace with sea-level rise (SLR). Oyster-reef abundance has already declined ⇠85% globally over the past 100 years, mainly from over harvesting3,4 , making any additional losses due to SLR cause for concern. Before any assessment of reef response to accelerated SLR can be made, direct measures of reef growth are necessary. Here, we present direct measurements of intertidal oyster-reef growth from cores and terrestrial lidar-derived digital elevation models. On the basis of our measurements collected within a mid-Atlantic estuary over a 15-year period, we developed a globally testable empirical model of intertidal oyster-reef accretion. We show that previous estimates of vertical reef growth, based on radiocarbon dates and bathymetric maps5,6, may be greater than one order of magnitude too slow. The intertidal reefs we studied should be able to keep up with any future accelerated rate of SLR (ref. 7) and may even benefit from the additional subaqueous space allowing extended vertical accretion.