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Coral growth and bioerosion as functions of temperature anomaly in west (W) and east (E), 7 m and 20 m depth. Coral growth rate of Porites lutea nubbins at all study sites (n = 20, df = 1, F-value = 4.4, r 2 = 0.46, p = 0.039) along the Similan island chain after 12 months exposure (February 2007 to February 2008; see Fig. 4) (A), and bioerosion (calculated mass change in calcium carbonate (CaCO 3 ) corrected for accretion due to fouling organisms) on CaCO 3 blocks at the central Similan island Ko Miang (see Fig. 1) after 12 months (grey depiction; February 2007 to February 2008; n = 4, degrees of freedom = 1, F-value = 14.4, r 2 = 0.30, p,0.001) and 21 months exposure normalized to 1 year (February 2007 to November 2008; n = 4, degrees of freedom = 1, F-value = 17.9, r 2 = 0.58, p,0.001) (see Fig. 5; ,0, bioerosion) (B) as functions (GLM) of the cumulative negative temperature anomaly (calculated as uC d) of the respective time period. All values are plotted as mean 6 SE. doi:10.1371/journal.pone.0073236.g007
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The Similan Islands (Thailand) in the Andaman Sea are exposed to large amplitude internal waves (LAIW), as evidenced by i.a. abrupt fluctuations in temperature of up to 10°C at supertidal frequencies. Although LAIW have been shown to affect coral composition and framework development in shallow waters, the role of LAIW on coral growth is so far unk...
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Context 1
... calculated with coral growth or bioerosion as dependent variable and temperature anomalies calculated for the respective exposure periods as independent variables. The results show that both coral growth (r 2 = 0.46, p = 0.039) and bioerosion after 12 (r 2 = 0.30, p,0.001) and 21 months exposure (r 2 = 0.59, p,0.001) are inversely related to LAIW (Fig. ...
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... growth, compared to the monsoon affected (W 7 m) and sheltered (E 7 m, E 20 m) sites. This may be due to the combined effect of unfavourable environmental conditions, notably lower temperature, light and pH in W 20 m compared to the other sites [31]. The GLM analysis shows that coral growth rates correlated well with temperature anomaly (Fig. 7), under- scoring the potential role of LAIW in suppressing coral growth. The growth rates in W 7 m are important in assessing the relative importance of monsoon and LAIW for reef growth [32] by showing that monsoon exposure did not limit skeletal growth. It is likely that the high water motion here enhanced metabolic rates and ...
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... was highest in E and lowest in W (Fig. 6) and showed an inverse relationship with temperature anomaly (Fig. 7) refuting our hypothesis of LAIW-(i.e. nutrient-) enhanced bioerosion. However, bioerosion has also been shown to be related to coral cover [2,14], in line with the observation of higher reef development in E [31,32]. This is because higher coral cover provides more habitats for internal and external bioeroders, notably living space for ...
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... This region is a good demonstration, however, that favorable conditions imposed by IGWs are not necessarily consistent yearround, because factors such as thermocline depth, tidal range, and other oceanic and atmospheric forcings also determine if and when thermal conditions are present at depths beneficial to reefs. IGWs can have detrimental effects on reefs as well, such as depressing coral growth (Schmidt and Richter, 2013) or limiting the maximum depth of reef development (Wyatt et al., 2020). The Galaṕagos and eastern Pacific locations, for example, experience a deepened thermocline during El Niño events so that IGW-induced cooling would be diminished. ...
Coral reefs are highly threatened by ocean warming and the majority are likely to be lost in less than three decades. A first step in maximizing reef conservation through this period is to identify where coral reefs are more likely to survive rising ocean temperatures, such as locations that experience lower temperatures than surrounding regions, high temperature variability, and high food supply. Such conditions are often the result of naturally occurring internal gravity waves (IGWs), oscillatory subsurface disturbances that can entrain cooler and/or nutrient-rich subsurface waters and cause high frequency temperature fluctuations. These features usually remain undetected because they occur subsurface and at spatial scales of O(1 km) and smaller. To shed light on where IGWs are likely to impact temperature conditions within coral reef regions, we present an analysis of data from the LLC4320, a massive high resolution (1/48˚; < 2.5 km) numerical global ocean simulation. The results highlight strong regional differences in the incidence of IGW-induced temperature variability. The analysis also reveals that thermal refugia are limited to depths where high temperature variability coincides with the actual reef depth and may not persist year-round. Assuming 10-m depth as the nominal reef depth, reef regions likely to benefit from IGW-induced cooling occur in SE Asia and the Coral Triangle, the Galápagos, along the Pacific shelf of Central America, and isolated locations worldwide. Such refugia are rare within the Atlantic reef sector. An interactive global atlas showing the results of this study has been made freely available online at https://ncar.github.io/coral-viz/.
... Generally, most block assay studies conducted in various reef habitats and regions found net-erosive rates. For instance, studies from reefs in the Thai Andaman Sea and Indonesian Java Sea found that the accretion by calcifying crusts, such as coralline algae, were negligible compared to the high degree of bioerosion measured in the limestone blocks (Edinger et al., 2000;Schmidt and Richter, 2013). In contrast, our limestone block assays captured a substantial net accretion rate, in particular for the offshore reef site in the central Red Sea (0.37 kg CaCO 3 m −2 yr −1 net accretion), indicating that accretion was substantial, while erosion was negligible. ...
... kg CaCO 3 m −2 yr −1 , 30 months deployment). This is a moderate rate compared to the larger net erosion observed in the GBR, French Polynesia, and Thailand (−4 or −8 kg CaCO 3 m −2 yr −1 ) (Osorno et al., 2005;Pari et al., 1998;Schmidt and Richter, 2013;Tribollet and Golubic, 2005). ...
The structural framework provided by corals is crucial for reef ecosystem function and services, but high seawater temperatures can be detrimental to the calcification capacity of reef-building organisms. The Red Sea is very warm, but total alkalinity (TA) is naturally high and beneficial for reef accretion. To date, we know little about how such detrimental and beneficial abiotic factors affect each other and the balance between calcification and erosion on Red Sea coral reefs, i.e., overall reef growth, in this unique ocean basin. To provide estimates of present-day reef growth dynamics in the central Red Sea, we measured two metrics of reef growth, i.e., in situ net-accretion/-erosion rates (Gnet) determined by deployment of limestone blocks and ecosystem-scale carbonate budgets (Gbudget), along a cross-shelf gradient (25km, encompassing nearshore, midshore, and offshore reefs). Along this gradient, we assessed multiple abiotic (i.e., temperature, salinity, diurnal pH fluctuation, inorganic nutrients, and TA) and biotic (i.e., calcifier and epilithic bioeroder communities) variables. Both reef growth metrics revealed similar patterns from nearshore to offshore: net-erosive, neutral, and net-accretion states. The average cross-shelf Gbudget was 0.66kg CaCO3m⁻²yr⁻¹, with the highest budget of 2.44kg CaCO3m⁻²yr⁻¹ measured in the offshore reef. These data are comparable to the contemporary Gbudgets from the western Atlantic and Indian oceans, but lie well below optimal reef production (5–10kg CaCO3m⁻²yr⁻¹) and below maxima recently recorded in remote high coral cover reef sites. However, the erosive forces observed in the Red Sea nearshore reef contributed less than observed elsewhere. A higher TA accompanied reef growth across the shelf gradient, whereas stronger diurnal pH fluctuations were associated with negative carbonate budgets. Noteworthy for this oligotrophic region was the positive effect of phosphate, which is a central micronutrient for reef building corals. While parrotfish contributed substantially to bioerosion, our dataset also highlights coralline algae as important local reef builders. Altogether, our study establishes a baseline for reef growth in the central Red Sea that should be useful in assessing trajectories of reef growth capacity under current and future ocean scenarios.
... Compared to the sheltered site, the exposed site features higher temperature fluctuations (up to 6-9 °C) and pH variability (by up to 0.6 units) that last for 15-30 min, higher nutrient and lower oxygen levels ( Schmidt et al., 2012;Wall et al., 2012Wall et al., , 2014). As a result, LAIW-exposed corals show higher nutritional status ( Roder et al., 2010Roder et al., , 2011), higher feeding capacity and higher photosynthetic efficiency ( Pacherres et al., 2013) but lower growth ( Schmidt and Richter, 2013). LAIW and monsoon impact are disturbances that depress framework development ( Schmidt et al., 2012). ...
Large-amplitude internal waves (LAIW) cause intense drops in sea water temperature (6–9 °C) and acidity (0.6 pH units) within minutes, posing a major disturbance factor for shallow water corals in the Andaman Sea. During periods of elevated temperatures, however, they may provide a vital source of relief to heat-stressed corals. To assess the effect of LAIW on the thermal tolerance of the massive coral Porites lutea, we carried out a one-month reciprocal LAIW simulation experiment with coral nubbins collected from the LAIW-exposed and LAIW-sheltered sides of the Similan Islands, an offshore archipelago near the Thai Andaman shelf break (distance of sampling locations < 3 km). Corals from either origin were subjected to (1) ambient (29 °C, pH 8.39) vs. elevated (31.5 °C) temperatures; and (2) ambient temperatures with simulated LAIW (30 minute drops to 23.8 °C, pH 7.9, twice per day) vs. elevated temperatures with LAIW (30 minute drops to 24.9 °C, pH 7.9, twice per day). Simulated LAIW reduced heat stress responses in all corals. However, nubbins from the LAIW-exposed site showed a higher tolerance to the heat stress than sheltered corals, i.e. lower bleaching- and mortality rates, higher photosynthetic performances and higher protein contents at the end of the experiment, despite identical algal symbiont genotypes (ITS-2, C15). Our results suggest that LAIW-induced nutrient availability, enhanced heterotrophic feeding and thermal variability increased the upper thermal resistance of P. lutea, supporting the notion that LAIW-exposed reefs might be important refugia for coral survival in a warming ocean.
... When they reach shallow waters, they bring up cold, nutrient-enriched water from below the pycnocline (Vlasenko & Stashchuk 2007, Wall et al. 2012. Therefore, they may have an important, yet so far mainly unknown impact on the development of coral reefs and coral growth (Wall et al. 2012, Schmidt & Richter 2013. ...
... At the Similan Islands, the impact of LAIW on scleractinian corals declines accordingly from exposed W deep to shallow waters, followed by sheltered E deep and shallow sites (Roder et al. 2011). In addition, highest temperature fluctuations (a proxy for LAIW) can be observed at the west side with increasing depths from February until April leading to the assumption that LAIW-intensity peaks in spring , Wall et al. 2012, Schmidt & Richter 2013. Therefore, coral reef development only occurs at the east side of the islands, whereas the ocean facing, west side lacks an actual reef framework due to more intense upwelling and wave action (Schmidt 2010, Wall et al. 2012. ...
... Hence, the positive correlation of LAIW with depth is likely responsible for the reduced framework at deeper depths . Reduced growth of P. lutea was also found at W 20 m due to the unfavourable environmental conditions originating from LAIW (Schmidt & Richter 2013). In contrast, the monsoon exposure had no negative effect on coral growth (Schmidt & Richter 2013). ...
The Similan Islands, a chain of islands in the Andaman Sea, are subject to large amplitude internal waves (LAIW, or solitons) and the southwest monsoon. The ocean facing west side of this archipelago near the Thai continental shelf break is exposed to LAIW and monsoon, whereas the eastern side is sheltered from both. LAIW mainly influence greater depth and are known to change environmental factors that affect coral growth. The monsoon however, causes higher wave action and increased sedimentation and therefore primarily influences shallow reef areas.
In the present study, the impact of LAIW and monsoon on linear extension rate, skeletal bulk density and calcification rate of the scleractinian coral Porites lutea are investigated. Coral skeletons have been collected at two depths (7 and 20 m) at the west and east sides of the central Similan island Ko Miang. X-radiography and fluorescence analysis are used to examine the linear extension rate due to the annual banding in the coral skeletons. Measurements of skeletal bulk density, micro-density and porosity are based on the buoyant weighing technique, calculation of the total enclosed volume and measurement of matrix volume by Archimedean methods.
Higher skeletal bulk densities were found at the west side of the island Ko Miang with highest values at W 7 m. As no correlation of the skeletal bulk density with the intensity of LAIW was found, higher density values could be attributed to the impact of the monsoon. For the linear extension and calcification rates, no significant differences between side and depth were observed. In addition, no correlation with the intensity of internal waves was discovered, which indicates that other environmental factors than internal waves primarily affect growth and calcification of P. lutea.
... Because LAIW are ubiquitous in tropical areas, they may play a major role in sustaining coral diversity and cover in a warming climate. LAIW exposure is, however, a 'mixed blessing', as it hampers reef development [15,16] and coral growth [70], but promotes high diversity [15] and coral fit- ness [58,59] under prevailing conditions (i.e. non-bleaching) that might prove essential for reef persistence in this area. ...
Tropical scleractinian corals are particularly vulnerable to global warming as elevated sea surface temperatures (SSTs) disrupt the delicate balance between the coral host and their algal endosymbionts, leading to symbiont expulsion, mass bleaching and mortality. While satellite sensing of SST has proved a reliable predictor of coral bleaching at the regional scale, there are large deviations in bleaching severity and mortality on the local scale that are poorly understood. Here, we show that internal waves play a major role in explaining local coral bleaching and mortality patterns in the Andaman Sea. Despite a severe region-wide SST anomaly in May 2010, frequent upslope intrusions of cold sub-pycnocline waters due to breaking large-amplitude internal waves (LAIW) mitigated coral bleaching and mortality in shallow waters. In LAIW-sheltered waters, by contrast, bleaching-susceptible species suffered severe bleaching and total mortality. These findings suggest that LAIW benefit coral reefs during thermal stress and provide local refugia for bleaching-susceptible corals. LAIW are ubiquitous in tropical stratified waters and their swash zones may thus be important conservation areas for the maintenance of coral diversity in a warming climate. Taking LAIW into account can significantly improve coral bleaching predictions and provide a valuable tool for coral reef conservation and management.
... Reef bioerosion rates respond strongly to eutrophication (e.g. Rose & Risk 1985, Holmes 2000, Le Grand & Fabricius 2011 and substrate type (Highsmith 1981, Risk et al. 1995, Edinger & Risk 1996, Perry 1998, Schönberg 2002. Distance from shore (Risk et al. 1995, Tribollet et al. 2002) and depth (Perry 1998, Le Grand & Fabricius 2011, Schmidt & Richter 2013 are also common correlates of bioerosion rates. However, the in situ response of erosion rates to pH and temperature -the variables most relevant to climate change -remains poorly characterized. ...
... Sampling technique. Previous studies have identified nutrient concentration (e.g. Rose & Risk 1985, Holmes 2000, Le Grand & Fabricius 2011, chlorophyll (Le Grand & Fabricius 2011), temperature (Davidson et al. 2013), pH (Tribollet et al. 2009, Wisshak et al. 2012, 2013, Reyes-Nivia et al. 2013, Fang et al. 2013) and depth (Perry 1998, Le Grand & Fabricius 2011, Schmidt & Richter 2013 as possible drivers of the accretionerosion balance. This study compared the effect of these environmental parameters on net accretionerosion using data obtained from discrete water samples (pH, TA, nitrate (NO 3 -), nitrite (NO 2 -), ammonium (NH 4 + ), phosphate (PO 4 3-), and chlorophyll a) and from continuous sensors (temperature and depth) along the transect. ...
... The pH model ranked higher than the distance, depth, and resource availability models; prior studies where depth, distance, and resource availability were stronger predictors of bioerosion were performed on much larger spatial scales and covered a greater range of values (e.g. Perry 1998, Tribollet et al. 2002, Le Grand & Fabricius 2011, Schmidt & Richter 2013. For instance, a prior study showing a strong response of bioerosion to resource availability had mean chlorophyll a values ranging from 0.25 to 1.24 µg l −1 across their comparison sites , compared to a range of only 0.14 to 0.31 µg l −1 in this study (Fig. 1). ...
Coral reefs persist in an accretion-erosion balance and ocean acidification resulting
from anthropogenic CO2 emissions threatens to shift this balance in favor of net reef erosion.
Corals and calcifying algae, largely responsible for reef accretion, are vulnerable to environmental
changes associated with ocean acidification, but the direct effects of lower pH on reef erosion
has received less attention, particularly in the context of known drivers of bioerosion and natural
variability. This study examines the balance between reef accretion and erosion along a wellcharacterized
natural environmental gradient in Ka¯ne‘ohe Bay, Hawai‘i using experimental
blocks of coral skeleton. Comparing before and after micro-computed tomography (μCT) scans to
quantify net accretion and erosion, we show that, at the small spatial scale of this study (tens of
meters), pH was a better predictor of the accretion-erosion balance than environmental drivers
suggested by prior studies, including resource availability, temperature, distance from shore, or
depth. In addition, this study highlights the fine-scale variation of pH in coastal systems and the
importance of micro habitat variation for reef accretion and erosion processes. We demonstrate
significant changes in both the mean and variance of pH on the order of meters, providing a local
perspective on global increases in pCO2. Our findings suggest that increases in reef erosion, combined
with expected decreases in calcification, will accelerate the shift of coral reefs to an erosiondominated
system in a high-CO2 world. This shift will make reefs increasingly susceptible to
storm damage and sea-level rise, threatening the maintenance of the ecosystem services that coral
reefs provide
Tides and tidally generated waves play a key role in modulating the heat budget of the nearshore environment, which can significantly affect the ecology of the coastal and reef zones. The high spatial resolution required to resolve such waves in numerical models means that diagnosing wave‐generated heat fluxes (WHFs) has so far only been possible over very limited areas. Because many marine ecosystems that are affected by WHFs, such as coral reefs, are patchily distributed within domains of hundreds of kilometers, an alternative to fully wave‐resolving models is needed to identify thermal refugia and guide conservation efforts over larger regions. In this study, a one‐way nested series of regional ocean simulations has been conducted to study the role of waves in driving high‐frequency temperature variations in the Coral Triangle and to develop a method for identifying WHF in coarser‐resolution models. A filtering method using Lagrangian particles is used to separate the wave component of the flow, which is used to diagnose the wave energy and to identify locations experiencing large, high‐frequency temperature variability. These locations are shown to possess three key characteristics: large time‐mean wave kinetic energy, shallow depth, and a steep bathymetric gradient that gives access to a nearby source of cold, subthermocline water. A function of the wave kinetic energy and bathymetric slope is found to closely correlate with areas of maximal temperature variance, suggesting its use as a convenient and readily calculable metric to locate thermal refugia in observations or numerical experiments over large spatial domains.
The coral structural framework is crucial for maintaining reef ecosystem function and services. Rising seawater temperatures impair the calcification capacity of reef-building organisms on a global scale, but in the Red Sea total alkalinity is naturally high and beneficial to reef growth. It is currently unknown how beneficial and detrimental factors affect the balance between calcification and erosion, and thereby overall reef growth, in the Red Sea. To provide estimates of present-day carbonate budgets and reef growth dynamics in the central Red Sea, we measured in situ net-accretion and net-erosion rates (Gnet) by deployment of limestone blocks to estimate census-based carbonate budgets (Gbudget) in four reef sites along a cross-shelf gradient (25 km). In addition, we assessed abiotic (i.e., temperature, inorganic nutrients, and carbonate system variables) and biotic (i.e., calcifier and bioeroder abundances) variables. Our data show that aragonite saturation states (Ω = 3.65–4.20) were in the upper range compared to the chemistry of other tropical reef sites. Further, Gnet and Gbudget encompassed positive (offshore) and negative (midshore-lagoon and exposed nearshore site) carbonate budgets. Notably, Gbudget maxima were lower compared to reef growth from undisturbed Indian Ocean reefs, but erosive forces for Red Sea reefs were not as strong as observed elsewhere. In line with this, a comparison with recent historical data from the northern Red Sea suggests that overall reef growth in the Red Sea has remained similar since 1995. When assessing reef sites across the shelf gradient, AT correlated well and positive with reef growth (ρ = 0.9), while temperature (ρ = −0.7), pH variation (ρ = −0.8), and pCO2 (ρ = −0.8) were weaker negative correlates. Noteworthy for this oligotrophic sea was the positive effect of PO43− (ρ = 0.7) on reef growth. In the best-fitting distance-based linear model, AT explained about 64 % of Gbudget. Interestingly, parrotfish abundances added up to 78 % of the explained variation, further corroborating recent studies that highlight the importance of parrotfish to reef ecosystem functioning. Our study provides a baseline for reef growth in the central Red Sea that will be particularly useful in assessing future trajectories of reef growth capacities under current and future ocean warming and acidification scenarios.
Ocean acidification imposes many physiological, energetic, structural and ecological challenges to stony corals. While some corals may increase autotrophy under ocean acidification, another potential mechanism to alleviate some of the adverse effects on their physiology is to increase heterotrophy. We compared the feeding rates of Galaxea fascicularis colonies that have lived their entire lives under ocean acidification conditions at natural carbon dioxide (CO2) seeps with colonies living under present-day CO2 conditions. When provided with the same quantity and composition of zooplankton as food, corals acclimatized to high CO2 showed 2.8 to 4.8 times depressed rates of zooplankton feeding. Results were consistent over four experiments, from two expeditions and both in field and chamber measurements. Unless replenished by other sources, reduced zooplankton uptake in G. fascicularis acclimatized to ocean acidification is likely to entail a shortage of vital nutrients, potentially jeopardizing their health and survival in future oceans.
