Category Archives: Rachel King

Coral Growth with Thermal Stress and Ocean Acidifi-cation

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In order to examine the effects of ocean acidification on coral growth rates, D. Manzello (2010) measured the extension rates of six different coral species over a two-year period. The values for growth rate obtained by Manzello were compared to values reported in primary literature to determine the change in growth rate over a period of about thirty years. Of the species examined, the linear extension of one of the most important reef building coral species, Pocillopora damicornis, declined by almost one-third over a thirty-two year period. The extension rates of the coral P. elegans were found to be fairly consistent with the P. damicornis results, showing a similar decline in growth rate of the coral. The extension rates of the massive coral species examined showed little change between the study and the twenty-seven year period before. Even with the decline in growth rate, the two Pocillopora species still had a much higher growth rate than the massive species. The density and calcification of the corals was also highest in the Pocillopora species. Two Pavona species showed similar or higher growth rates where Ω (a measure of the concentration of CO32- ions) was lower, in contrast to the Pocillopora species, which had higher extension rates at higher Ω values. Although seawater temperature and coral growth strategy also play a role in determining the response of corals to changing ocean chemistry, the combination of results shows that the branching Pocillopora species are potentially more vulnerable to ocean acidification. As the dominant species in the area, this could affect coral reef composition if ocean acidification continues. — Rachel King
Manzello, D., 2010. Coral growth with thermal stress and ocean acidification: lessons from the eastern tropical Pacific. Coral Reefs 29, 749–758.

The species studied in this investigation included Pocillopora damicornis, Pocillopora elegans, Pavona clavus, Pavona gigantea, Pavona varians, and Gardineroseris planulata. Corals were placed at various reef sites by tying coral colonies to a rebar hammered into a reef 2–3 m below the low tide line. The water temperature was recorded on temperature loggers every 30 minutes for the duration of the coral deployments. The corals were collected after one year, and the extension, density, and calcification for each coral species was determined from the samples. In massive corals, each coral was sliced perpendicular to the growth axis and growth was measured with a ruler to the nearest millimeter. On the branching corals, growth was measured for each branch with calipers after slicing the branch tips adjacent to the top of the stain line.
            In addition to the decline in extension rate of the main reef building coral P. damicornis near Panama, a decline in extension rate was also noticed in Costa Rica, indicating a potential large-scale factor contributing to the decreasing extension rate in the eastern Pacific Ocean. The extension rates of the massive coral species were not shown to change over a twenty-seven year period, although the extension rates were still half that of the Pocillopora species. In general, the average density of each species was shown to be inversely related to the mean extension rate in every species except P. varians, though the relationship was only significant in P. damicornis. P. damicornis also displayed lower extension rates in water with low Ω values, which is the saturation state of carbonate minerals in seawater. Locations with lower Ω values are expected to be more affected by ocean acidification.
            The author also discusses how coral growth strategy and temperature effects could influence the growth of corals in the future. Four models were discussed for declining coral growth rate: cumulative ocean acidification, acute thermal stress, and the combined thermal stress and acidification either as additive or synergistic effects. Depending on which model is most accurate, the effects of acidification on coral growth rate could vary significantly. In spite of this, the study shows that continuing acidification of the ocean from the anthropogenic input of CO2 into the atmosphere has the potential to significantly effect the growth of the branching Pocillopora coral species in the Pacific ocean. 

Impacts of Tropical Beaches by Tourists and Island Residents Result on Fringing Coral Reefs

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To determine whether lower percent coral cover is correlated with increased human activity, Juhasz et al. (2010) studied the relationship between the numberof visitors to a beach and the condition of the reef adjacent to that beach. The authors compared the amount and types of human use at five beaches on Moorea in French Polynesia to the total coral abundance, relative abundance of branching versus massive coral species, size distribution, and nutrient levels. The authors found a significant difference in the number of people per 1000 m across the five sites, with site 1 having the most visitors by a factor of 4. The other 4 sites had about the same number of visitors. The percent coral cover was lowest at site 1 (4.8%), which was significantly lower than sites 2–4 but not significantly different than site 5. The relative cover of branching and massive coral also varied significantly, with almost no branching coral at site 1 and only between 1% and 5% at the other sites. Small corals dominated the reef composition, though site 4 exhibited a more even distribution of sizes than the other sites. The nutrient levels were not found to vary significantly among the sites studied. The results of this study support the relationship between coral community composition and the number of visitors to a beach. High use areas are more likely to have damaged and weak coral communities, though more research needs to be done to determine exactly which activities harm the coral reefs. — Rachel King
Juhasz, A., Ho, E., Bender, E., Fong, P., 2010. Does use of tropical beaches by tourists and island residents result in damage to fringing coral reefs? A case study in Moorea French Polynesia. Marine Pollution Bulletin, doi:10.1016/j.marpolbul.2010.08.011.

            The sites in this study were selected because they were either highly used beaches or beaches in relatively pristine condition, to provide contrast in the data between high- and low-use areas. The reefs studied were “fringing” reefs, or reefs in shallow enough water that they could be walked on. All the sites experienced similar wave action, wind, and flow because they were all located on the north shore of the island. To quantify the number of beach users at each study site, the authors counted the number of people on the beach and in the water up to a depth of 2 m. Counts were done on a Sunday, Monday, and Tuesday every 30 min between the hours of 10:00 am and 4:00 pm. They also measured the length of the shoreline, and took the average of the counts and divided them by the shore length to get the number of people per 1000 m.
Benthic cover was determined by laying four 25 m transects at random compass bearings and randomly placing five quadrats (1×1 m) along the transect. The percent cover of each coral species or algae was determined and then the average percent coral cover was found for each site, and the authors used a single-factor ANOVA to determine if percent cover of total coral, branching and massive, and algae were significantly different between sites. The number and sizes of corals within 1 m of the transect on either side was also recorded, although only Porites lobata and Acropora spp. were counted since they were the most common coral species at all sites. The last part of Juhasz et al.’s study involved a nutrient analysis of the five sites. They collected samples of the algae Acanthophora spicifera, which they used because it responds quickly to increased nutrient supply, from one site along the north shore of Moorea. The algae were cultured in low nutrient, flowing seawater and then spun in a salad spinner to remove excess water. Five grams of the algae were then placed in each of five mesh bags, sewn shut and then placed at each site. The bags were attached to a hard substrate and collected after five days, then weighed again to determine the growth. A two-factor ANOVA was performed to determine if the growth rates differed significantly between algae at different sites. However, the results for the macroalgae growth did not vary significantly between any of the sites, therefore it is unlikely that nutrient supply varied significantly between the sites.
            The counts of people showed that site 1 had more visitors by a factor of four, and that the other four sites did not display significantly different numbers of visitors. However, site 4 was mainly visited by local residents, not tourists, and was mainly used for picnicking, so the potential for human impact on the reefs was lower. Site 1 also had the lowest percent coral cover (4.8%), while sites 2, 3, and 4 all had 21.4–51.5% percent coral cover. Site 5 was not significantly different from site 1, with coral cover of 15.6%. The differences in percent coral cover between the sites correlated with the differences in the numbers of people visiting each site, since site 1 was the most visited site and also had the lowest percent coral cover. There were also significant differences in the composition of the coral communities. At site 1, there were almost no branching coral, while other sites had between 1% and 5% percent coral cover. The massive coral was more abundant, and also had the lowest percent cover at site 1, while the other sites ranged between 12% and 51% percent coral cover. The number of massive coral colonies, Porites lobata, at each site varied, but was not correlated with human use, while the number of branching colonies was significantly smaller at site 1 than at the other four sites. The size frequency distribution for P. lobata also varied, but still was not correlated with human use. For the Acropora spp., site 1 had only the smallest size class present, and smaller corals also dominated sites 2, 3, and 5 even though they possessed some colonies of larger size. Site 4 was unique in respect to both coral species because it had a more even distribution of size classes.

The results of this study show a significant correlation between a high use area (a large number of visitors) and lower percent coral cover. The low amount of the branching coral and the lowest ratio of branching to massive coral present at the highest use site also suggests that branching corals may be more sensitive to human activities and may decline faster unless protective measures are taken. Though the authors do not know which specific activities have the most impact on corals, if further studies determined which activities were the most detrimental, restrictions could be placed on certain beach activities to help preserve coral colonies near high use areas. 

The Potential of Small Caribbean Marine Pro-tected Areas for Ecosystem Preservation

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Kopp et al. (2010) examined whether small, established marine reserves could effectively sustain a coral reef ecosystem by enhancing the fish stocks and limiting macroalgae growth. The authors studied two marine protected areas (MPAs) around the island of Guadeloupe, one located around Ilets Pigeon and one in the bay of the Grand Cul-de-Sac Marin, and five non-protected reefs for comparison with the protected reefs. Surveys of the fish and benthic communities revealed that although the mean number of individuals per 100 m2 was about the same in MPAs as in non-MPAs, the mean biomass of herbivorous fishes was significantly larger inside MPAs, indicating the presence of larger fish in the MPAs. The study also reported a significantly lower cover of macroalgae in the MPAs than in the non-protected areas, and a significant negative correlation between benthic macroalgal cover and herbivorous fish biomass. Though there was no evidence in the study of the benefits of MPAs extending over their boundaries, they were shown to increase fish biomass and manage macroalgal cover, which contributed significantly to sustaining coral reef ecosystems. — Rachel King
Kopp, D., Bouchon-Navaro, M., Mouillot, D., Bouchon, C., 2010. Herbivorous fishes and the potential of Caribbean marine reserves to preserve coral reef ecosystems. Aquatic Conservation: Marine and Freshwater Ecosystems 20, 516–524.

            Within the two MPAs studied, five reef sites were sampled between 1 and 10 m in depth, and the five non-protected reef sites were also sampled between these depths. Visual surveys of fish were performed twice in both the dry and rainy seasons using a 150 x 2 m transect, which provided estimates of fish abundance in terms of density and biomass. Fish were identified to the species level and their length recorded in 5 cm size classes for fish fewer than 20 cm and in 10 cm classes for fish larger than 20 cm. The biomass of fish was estimated using weight-length relationships from the literature. For scarid fish, the phase (initial or terminal) was also noted. While the fish survey was conducted, the benthic community composition was estimated by recording the types of benthic organisms present at every meter along the 150 m transect.
To analyze the collected data, the authors used a canonical analysis of principal coordinates (CAP), which allows a constrained ordination to be performed on the basis of any distance. The response of the whole fish assemblage in the MPAs was analyzed, followed by examining each species. Benthic cover between MPAs and non-protected areas was compared and a correlation between benthic cover and herbivorous fishes was found using the non-parametric Spearman rank correlation coefficient.
            The mean number of individuals per 100 m2 in the MPAs (87.4±22.3 (SE)) was very close to the value outside the MPAs (86.3±22.3 (SE)). This pattern was also observed for the number of scarid fishes inside and outside the MPAs. However, both the total assemblage of fish and scarid fish showed a larger biomass inside the MPAs. Although a few species had higher abundances outside the MPAs, most had larger numbers and biomass inside the reserves and therefore indicated a significant reserve effect on those species. The size class of species also differed significantly between the two types of areas. Large adults of three species, Scarus vetula, Sparisoma rubripinne, and S. viride, that were also in their terminal phase were only found within MPAs, and Acanthurus bahianus only had medium-sized individuals present within MPAs. The results also showed that the mean percentage of terminal males was 22% inside MPAs, whereas it was only 10% outside the reserves. Significant correlations were also found between coral cover and the biomass of large herbivorous fishes, biomass of large herbivorous fishes and macroalgal cover (negative correlation), and macroalgae and algal turf (negative correlation).

The results indicate that marine protected areas are having a significant effect on the biomass of herbivorous fishes in the Caribbean, which especially indicates their importance as a refuge for larger fish. The importance of even small MPAs is accentuated by the results showing that certain terminal phase fish are only found within MPAs. The coral reef communities were also more stable inside the MPAs due to the larger percent coral cover, increased fish stock, and lower algal cover. This study adds significant support to the need to maintain or increase the amount of MPAs to help preserve coral reef communities.

Conservation Management Approaches to Pre-serving Coral Response to Climate Change

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To help determine the best conservation management plans for coral reefs, Baskett et al. (2010) created a model examining the importance of certain parameters and processes in determining the response of coral and symbiont populations to climate change. The model used varying initial conditions in those parameters to explore model predictions of coral cover in different future climate scenarios, using a quantitative analysis to enhance the understanding of which characteristics best indicate coral capacity to respond to climate change. The model used past temperature data and two future climate predictions, with either higher or lower greenhouse gas emissions, in the model calculations. The results of the model indicate that protecting diverse coral communities with some thermally tolerant coral species and symbionts, mitigating additional anthropogenic impacts on coral communities, and protecting and connecting locations with oceanographic features that lead to lower thermal stress should be priorities in management plans to best preserve coral communities.–Rachel King
Baskett, M., Nisbet, R., Kappel, C., Mumby, P., Gaines, S., 2010. Conservation management approaches to protecting the capacity for corals to respond to climate change: a theoretical comparison. Global Change Biology 16, 1229–1246.

The model created by the authors involves 21 parameters, distributed among macroalgae, corals, and symbionts. Their study included an examination of symbiont genetic dynamics, symbiont population dynamics, coral population dynamics, and coral community dynamics. To increase the model’s relevance, the authors integrated the model with past and future temperature data and used a variety of initial conditions in the parameters they investigated. The key predictions developed by the model include examining coral cover under future climate scenarios: with varying initial conditions to determine the importance of a higher abundance of stress-tolerant corals or symbionts in respect to the overall diversity of an area; in several locations to compare how past thermal stress affected coral cover and stress tolerance, along with the possibility for future thermal stress in those locations; with and without larval connectivity to help examine the importance of new recruitment versus maintaining local coral adaptations. The study used two species of coral, one massive-type (Montastraea annularis) and one branching-type coral, Pocilloporidae, to represent the types of coral present in a coral community.
The authors tested the model predictions using past monthly sea surface temperature data and future temperature predictions from different climate models and locations. The past temperature data came from the Met Office Hadley Centre for Climate Prediction Sea Ice and SST data set (ISST). The authors derived future temperature data from two climate models¾the Hadley Center HadCM3 model and the National Oceanic and Atmospheric Administration (NOAA) Geophysics Fluid Dynamics Laboratory 2.1 model. The study also compared future climate scenarios with different greenhouse gas emissions, one where emissions stabilize at 720 ppm and another where emissions stabilize at 550 ppm. This emission range gives values for business-as-usual greenhouse gas emissions and for large-scale mitigation efforts. The authors obtained future temperature data for their climate models and scenarios from the World Climate Research Programme’s Coupled Model Intercomparison Project phase 3 multimodel dataset.
The model runs varying the initial conditions of coral symbiont diversity showed similar long-term results under both of the possible emission futures. In all cases, the branching-type coral cover decreases over the century time scale even if the species begins with a higher abundance. In the higher-emission future scenario, the massive-type coral cover also ends up decreasing over the time scale, but in the lower-emission scenario they eventually end up at a higher coral cover than the branching-type coral even when they begin with a lower coral cover. Similar results were obtained with the stress-susceptible and stress-tolerant symbionts: the stress-tolerant symbiont remains or becomes the dominant symbiont in each scenario. These results indicate that protecting diverse coral communities with stress tolerant species is a higher priority than protecting locations with a large abundance of stress tolerant species.
The model runs with macroalgae demonstrated that when coral cover dropped below a certain threshold, the macroalgae population increased dramatically due to decreased competition for space with the corals. Because macroalgae can impede the recovery of corals after disruptive events such as bleaching, the authors highlight the importance of mitigating anthropogenic contributions to macroalgae growth. Proposed management options include protecting healthy populations of herbivorous fish from over fishing, monitoring and limiting runoff of anthropogenic inputs that increase macroalgal growth, and preventing runoff that decreases the population of herbivorous fish. Model results also indicate that regions with past thermal stress are more likely to have future thermal stress events that even heat-adapted corals cannot respond to. Therefore, focusing management efforts on regions with low predicted future stress and lower bleaching occurrences could help maximize the reefs that survive climate change. Furthermore, the model indicated that there were more positive effects associated with coral recruitment, which outweighed the negative effects of an influx of new corals poorly adapted to thermal stress. This supports protecting regions that have the potential for continued coral recruitment.
This study highlights several important factors that conservation management plans should take into account in order to ensure the survival of as many coral reefs as possible. Protecting diverse coral communities with some heat-tolerant corals, limiting anthropogenic disruption of coral communities, and protecting areas with low potential for future heat stress and some connectivity to allow recruitment will help mitigate the effects of climate change on certain coral communities. Though many factors go into determining coral reserve locations, priorities should be made to protect coral communities possessing the characteristics emphasized by the authors’ model. 

Adaptive Potential of Coral

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This study examines the heritability of key traits used to respond to thermal stress in two populations of the coral Acropora millepora and their algal photosymbionts (Symbiodinium). Császár et al. (2010) assessed six traits in the symbiont population, four traits in the coral host population, and one holobiont trait for their heritability in either A. millepora or Symbiodinium, clades D or C2. Both algal symbionts showed a significant capacity to adapt to thermal stress in five of the six key traits examined, while clade D symbionts showed a higher estimate than the C2 symbionts. The coral host lacked heritability in three of the four traits examined, with only one trait exhibiting any significant heritability. The different heritability of heat stress traits in algal symbionts and their coral hosts demonstrates that although algal symbionts may be able to rapidly adapt to thermal stress, the host coral’s low trait heritability and long generation time could limit the ability of corals and their symbionts to adapt to warming climates.¾Rachel King
Császár, N., Ralph, P., Frankham, R., Berkelmans, R., H. van Oppen, M., 2010. Estimating the Potential for Adaptation of Corals to Climate Warming. PLoS One 5, 1–8.

            The authors obtained coral samples for the study from twenty colonies of A. millepora in a mid-shelf reef location in two different thermal environments along the Great Barrier Reef¾ Magnetic Island (MI) and Orpheus Island (OI)¾and transferred them to the Australian Institute of Marine sciences for testing. Analyzing the sequences of the nuclear ribosomal DNA internal transcribed spacer 1 (rDNA ITS1) identified the symbionts in both of the coral populations. Only type D Symbiodinium were found in coral colonies from MI, and only type C2 Symbiodinium were found in the colonies from OI. Heat stress experiments were performed for four clonal nubbins from each of the 20 colonies sampled by placing them in indoor tanks with a temperature of 27 ºC for two weeks before exposure to a temperature of 32 ºC for 15 days.
Following the heat stress experiment, the coral colonies were analyzed for trait heritability. Heritability was calculated by subtracting the environmental variance from the total phenotypic variance to determine the genetic variation (VG =VP – VE). Dividing the genetic variation by the total phenotypic variance (VG/VP) gave the heritability (H2). Photosynthesis energy pathways in symbionts were measured using non-invasive pulse amplitude modulated fluorometry, which gave information on the efficiency of photosystem II (PSII), regulated and unregulated energy dissipation in the light-adapted state and the maximum dark-adapted quantum yield of PSII fluorescence.
The symbiont traits examined included four parameters related to PSII chemistry and two traits concerning the PSII antenna pigment profile. The clade D Symbiodinium exhibited significant heritability in all of the traits except regulated non-photochemical quenching of excitation energy, suggesting that there is little or no adaptive potential for this trait in the MI’s symbiont population. Type C2 Symbiodinium showed heritability for all six traits except the maximum quantum yield of PSII. Both symbionts demonstrated the ability to change PSII pigments to increase photoprotection when under thermal stress. The heritability results suggest that the algal symbionts for A. millepora have high adaptive potential for photoprotective measures when introduced to thermal stress.
Each of the four coral traits examined were related to the gene expression of proteins aiding in thermal stress tolerance. However, each coral population exhibited heritability in only one of the four traits. The lack of heritability of these traits suggests that the coral populations have a low potential for adaptive changes in response to thermal stress. However, coral growth, the holobiont trait examined, showed significant heritability in both populations.
The lack of evolutionary potential of the genes in the corals indicates that the algal partner in the symbiotic relationship will largely determine A. millepora’s adaptive potential to climate warming. The low heritability of coral heat stress genes is also exacerbated by the fact that corals have longer generation times than their symbionts, meaning that even if the corals had heat stress genes that were heritable, it would take longer for them to adapt to a warming climate than their symbiotic algae. This has important implications for coral health, as sea surface temperatures are expected to rise by 2-3 ºC in the 21st century, so there is a substantial need for corals to adapt to a warming thermal environment. The authors’ results show that due to heritability of traits in corals and their symbionts, this adaptive ability is only likely to come from the algae. If their adaptive ability is not enough, the reefs of the world could see an increase in coral bleaching events and a substantial decline in coral populations throughout the world. 

New insights into global patterns of ocean temperature anomalies: implications for coral reef health and management

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In this study, Selig et al. (2010) created the Coral Reef Temperature Anomaly Database (CoRTAD) using data from the National Oceanic and Atmospheric Administration’s (NOAA) National Oceanographic Data Center (NODC) from 1985 to 2005. The data were used to calculate frequency, size, intensity, and duration of extreme thermal stress events that were associated with coral bleaching and disease. A baseline was also established to compare extreme temperature events and explore how the anomalies varied by region. Their data showed that the frequency of anomalies varied by year and region, and that 48% of coral bleaching related anomalies and 44% of disease related anomalies were smaller than 50 km2, which is a smaller resolution than most current models use. This indicates that more fine-scale models are needed to accurately predict the effects of climate change on corals, and that temperature anomalies influencing coral bleaching and disease are likely to vary significantly on smaller spatial scales producing fairly localized responses to climate change.  ¾ Rachel King
Selig, E., Casey, K., Bruno, J., 2010.  New insights into global patterns of ocean temperature anomalies: implications for coral reef health and management. Global Ecology and Biogeography 19, 397 – 411.

            The CoRTAD is a 21-year, 4-km resolution global dataset of ocean temperature anomalies that was developed with data from the Pathfinder Version 5.0 collection, produced by the NOAA’s NODC and the University of Miami’s Rosenstiel School of Marine and Atmospheric Science. The authors derived the sea surface temperature (SST) data from an Advanced Very High Resolution Radiometer (AVHRR) sensor, which was processed to a 4.6 km resolution at the equator. A day-night average of the data was used to increase the number of observations with no significant change in the accuracy. The CoRTAD was validated against in situ temperature loggers over a variety of coral locations and depths, and was accurate at most sites to within 0.11 ºC, less than the range of accuracy for the loggers themselves (± 0.2 ºC).
            The authors focused their analysis on two metrics – one associated with coral bleaching and one associated with disease severity These two factors are important drivers of coral decline, so analysis of these areas provides a clear indicator of temperature effects on coral populations. Thermal stress anomalies (TSAs) were the metric used for coral bleaching, and is categorized as temperatures that exceed the long-term average warmest week of the year by 1 ºC or more. Weekly sea surface temperature anomalies (WSSTAs) were the metric used for analyzing temperature correlations coral disease. WSSTAs are temperatures that are 1 ºC or more than the weekly climatological value. The authors also calculated the frequency of WSSTAs and TSAs over the 21-year period and the size of the anomalies in the tropics for anomalies that overlapped areas with known coral reefs.
            The frequency of TSAs and WSSTAs varied considerably across different regions. For all the 4-km grids containing reefs, the TSA frequency ranged from 37 anomalies to 444 over the 21-year period. The authors also examined the anomaly frequency by year to determine if there were more TSAs in recent years than in past years, but found that it varied by region. Some regions had the most extreme temperatures in the 1998 El Niño/Southern Oscillation (ENSO) event, but other regions had higher anomaly frequencies during the 1987-88 ENSO or the 2005 ENSO. However, the severity of the 1998 and 2005 ENSO events was apparent by the coral bleaching anomalies in those years. The size distributions of WSSTAs and TSAs were remarkably similar considering difference in number of occurrences for the two anomalies. Most anomalies had relatively small sizes and a higher number of occurrences. Large anomalies ( > 500 km2) represented less than 10% of data, with 33% of TSAs and 29% of WSSTAs in the size category between 1 and 25 km2.
            Current models for climate change are critical in helping determine patterns for ocean warming, and therefore areas of concern for conservation. However, most of these models have very coarse resolution, which can falsely display homogenous patterns of thermal stress. The authors’ results show that over 60% of bleaching and disease related anomalies occur at smaller scales than the resolution for many models for climate change. Therefore, to adequately understand the potential effects of climate change on ocean warming and bleaching or disease related events, finer scale models may be required. Their results can also help pinpoint areas for possible coral refuges based on the frequency and magnitude of thermal anomalies, though given the uncertainties in using past temperature data to predict the effects of future warming is still difficult. Large-scale events such as the 1998 ENSO could still produce massive bleaching even in areas identified as potential refuges. As such, the importance of accurate and appropriately sized data for climate change is a necessity according to the authors, and is important in determining conservation strategies for coral reefs in the future. 

Acclimation and adaptation of scleractinian coral communities along environmental gradients within an Indonesian reef system

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            A study of six key coral species, conducted by Hennige et al. (2010), examined coral distribution along environmental gradients within the Wakatobi Marine National Park reef system. Though the total number of coral species decreased from optimal coral reef sites to marginal sites, massive corals such as Goniastrea aspera tended to dominate in marginal sites, along with the symbiotic microalgae Symbiodinium type D, indicating more resilience to varying environmental conditions. In sites with optimal reef conditions, branching corals, such as P. cylindrica, were more abundant with the type C Symbiodinium. Marginal reef habitats are predicted to expand due to climate change; therefore, the success of massive coral species in marginal conditions could decrease branching coral diversity in reefs, changing the coral composition of the Indonesian and world reef system.  ¾ Rachel King
Hennige, S., Smith, D., Walsh, S., McGinley, M., Warmer, M., Suggett, D., 2010. Acclimation and adaptation of scleractinian coral communities along environmental gradients within an Indonesian reef system. Journal of Experimental and Marine Biology 391, 143–152.

            The authors selected five sites to study that provided a range of environmental conditions, with habitats classified from “optimal” to “marginal”. “Optimal” sites refer to areas of high coral diversity and abundance, while “marginal” sites exhibit highly variable conditions from optimal growth sites. Temperature and light were measured over two field seasons using HOBO temperature (ºC) and light (lux) loggers that were deployed for one-week periods to obtain minima and maxima data. The lux data were also used to determine daily changes in light level between sites. The wavelength-specific light attenuation coefficient, Kd(l), was calculated from radiometer data at each site, and the average, Kd (site), was used to calculate optical depth. This data enabled sites to be ranked from optimal to marginal growth locations. Marginal sites had higher values of Kd and higher diurnal range of light and temperature, while optimal sites had low light and temperature variability and low Kd (low turbidity) values.
            To determine the coral species present at each site, 50 m continuous line-intercept transects were used, but this method was modified at marginal sites to 50 x 2 belt transects. Metabolic and daily productivity assessments were performed by measuring oxygen concentration during respiration and photosynthesis. The oxygen drift per unit time was used to calculate hourly rates of respiration, net photosynthesis, and gross photosynthesis. Using a previous model, the authors calculated the maximum gross productivity, PG(D), of the corals, and they also calculated the daily respiration rate. Portions of the coral samples were used to genetically identify the Symbiodinium in the coral.
            The data from the light analysis of the sites, the Kd values and optical depth, demonstrated that marginal corals experienced higher and more variable light intensities than con-specific species on the optimal reefs. The authors’ results also illustrated a decrease in the number of coral species from optimal to marginal reefs, and a change in the morphological features of the corals. Optimal reefs had a higher presence of branching corals, while the marginal reefs contained only massive coral species. The metabolic data collected showed a species-specific trend for PG(D) compared to optical depth: PG(D) either increased or remained the same with lower optical depths. The results also showed a change in Symbiodinium community structure in optimal versus marginal reefs. Type C was observed in all the optimal sites, but as the sites became more marginal, type D became increasingly prominent until it was the only Symbiodinium identified at the most marginal site. G. aspera was the only coral reported to have different Symbiodinium clades at different sites.
            The authors propose several reasons for the dominance of massive corals at marginal sites. Massive corals are more stable than branching species, and some massive corals such as G. aspera have certain adaptations, such as heat shock proteins, to help protect themselves from marginal environments. These advantages, as well as the presence of type D Symbiodinium, a more resilient symbiont, all contribute to the prevalence of massive corals at marginal sites. The higher abundance of branching corals at optimal sites was attributed to the coral’s high reproductive rate and fast growth rate, so they can out compete massive corals under certain conditions. However, this study explains that if there is an increase in the amount of marginal coral locations, the massive corals that are more suited to tolerate a widely varying environment will probably dominate. This would result in a decrease in branching coral diversity, affecting reef biodiversity and ecosystem services and reef metabolism and accretion rates. Studying current marginal locations provides a good opportunity to examine possible future coral reef community structures in the face of climate change.
            

Climate Induced Coral Mortality Can Be Predicted by Sea-Surface Temperature Variability

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Ateweberhan et al. (2010) collected data from 36 major coral reef areas of the Western Indian Ocean (WIO) 1998 El Nino/Southern Oscillation (ENSO) event, and revealed important correlations between sea-surface temperature (SST) data and the 1998 coral bleaching. Although extreme sea-surface temperatures are a primary reason for coral bleaching, high standard deviation and high bimodality in the SST for an area, or a decrease in kurtosis and an increase in the standard deviation, were also linked to a large loss in percent coral cover. The authors show that it is possible to predict coral regions that are most resistant to change in the SST, which would enable more effective management policies to be put into place.—Rachel King
Ateweberhan, M., McClanahan, Tim R, 2010. Relationship between historical sea-surface temperature variability and climate change-induced coral mortality in the western Indian Ocean. Marine Pollution Bulletin 60, 964–970. 

 With temperature a key factor in influencing coral bleaching, this model shows important connections between temperature and coral mortality. Sites were sampled using haphazard or permanent Line Intercept Transects, and a site was used as a sampling unit. JCOMM-SST mean monthly data were collected and used to calculate the SST statistics. The average cover was determined when there were enough data points for a given site. The authors report their data as percent relative change in coral cover instead of percent absolute change in order to account for the initial cover, reducing the variations due to coral community structure.
Mean, median, minimum, maximum, standard deviation, skewness, kurtosis, and three bimodality indices were the calculated SST parameters for each area examined in the study. Standard deviation, skewness, kurtosis, and the bimodality indices were used as measures of variability in the SST data. After a Principal Components Analysis on the variables in SST, some were removed and only the standard deviation, skewness, kurtosis, and one bimodality index remained to be used in a final Principal Components analysis. The authors used a mixed model multiple regression analysis to find the SST factors that were correlated to the patterns in coral cover change.
After the 1998 climate event, the average coral cover in the WIO decreased by 37.72 ± 31.34%, even though there was great variation between the different regions. The variation included an increase in coral coverage in northwestern Madagascar (13.89 ± 23.89%) to a huge decline in the central atolls of the Maldives (95.72 ± 3.67%). Other results showed that a decrease in kurtosis, or peakiness of the data, was accompanied by an increase in standard deviation and a decrease in coral cover change. The areas studied that were the most resistant to warming exhibited weak bimodal SST distributions and moderate standard deviation, and they also had the least decline in coral cover. The results also showed that the Arabian/Persian Gulf region had strongly bimodal SST distributions and therefore were more likely to be susceptible to extreme temperatures. The results also suggest that a large decrease in the skewness of the SST would be accompanied by an increase in kurtosis and decrease in standard deviation, which would make that site more vulnerable to smaller warming events. These correlations between SST and the statistical analysis enable prioritizing of coral reef regions for conservation in order to best manage the effects of climate change.