Coral Condition Research Articles

Corals fail to recover at a Caribbean marine reserve despite ten years of reserve designation

The ability of reserves to replenish fish stocks is relatively well documented, but the evidence of their ability to induce positive effects on benthic communities remains inconclusive. Here, we test whether 10 years of reserve designation have translated into positive effects on coral communities in Glover’s Reef, Belize. Surveys of 87 patch reefs inside and outside the reserve revealed no clear indication of reserve implementation benefitting coral cover, coral colony size, or abundance of juvenile corals. Furthermore, massive broadcasting coral species exhibited greater losses over time than their smaller-sized counterparts across all sites, suggesting that local management actions have not alleviated the regional trend of high mortality for these species. We detected no difference in herbivorous fish abundances or macroalgal cover between reserve and fished sites, providing a potential explanation for the lack of cascading positive effects on the coral community. We conclude that patterns of regional coral decline are evident at Glover’s Reef, including a shift in dominance from broadcasting species to brooding species and declines in mean colony size. Our findings suggest that regional stressors are overwhelming local management efforts and that additional strategies are required to improve local coral condition.

Relating landscape development intensity to coral reef condition in the watersheds of St. Croix, US Virgin Islands

Land-based sources of pollution are a major threat to the health of coral reefs. We report, for the first time, a study that relates coral reef condition to human modifications of the landscape. Stony coral community richness, cover, colony size, and density were assessed along with 3-dimen- sional coral cover in the near-shore waters of St. Croix, US Virgin Islands, in 2006 and 2007. Land use/land cover data (LULC, 2.4 m resolution) and a landscape development intensity (LDI) index, an indicator of human activity calculated from the LULC data, were used to explore relationships with coral indicators. The LDI index was more robust than other indicators of human activity, exhibiting negative correlations with stony coral colony density, taxa richness, colony size, and total coral cover. High variability observed in coral density and taxa richness was better explained when percent nat- ural land and average coral station depth were considered along with the LDI index. Percent imper- vious surface in the watershed was negatively correlated with 1 coral condition indicator, total coral cover. The LDI index is an effective landscape indicator of human impact on St. Croix corals, high- lighting the link between land-based human activity and marine ecosystems. Further development of this tool will aid in land use planning and prioritization of conservation efforts.

Assessment of Mortality, Bleaching, and Disease among Stony Corals and Fire Corals of Dominican Reefs: Post-2005 Caribbean Bleaching Event

This 2006 study looked into the health of reef communities on the western and northern coasts of Dominica (Lesser Antilles) to observe the recovery and current condition of stony corals and Millepora spp. Using the AGRRA v. 4.0 protocol and utilizing comparisons with a 2005 AGRRA implementation, old mortality decreased 21.0 m2 in surface area (p=0.12); while recent mortality increased in surface area to 14.40 m2 (p=0.01). Bleaching symptoms decreased by 68% (p<0.001) and disease prevalence increased from 8 to 41 colonies (p<0.05) for the diseases of highest occurrence between both study years. The 2006 patterns of increased recent mortality and numerically higher disease infected colonies suggest that the 2005 bleaching caused the weakening of corals, increased susceptibility to disease, and partial and/or complete mortality in 2006. The effect of elevated sea surface temperatures of the 2005 Caribbean bleaching event is likely a big contributor to the degraded health of the 2006 coral communities.

Acute tissue death (white syndrome) affects the microenvironment of tabular Acropora corals

White syndrome (WS) is a collective term for coral diseases that cause acute tissue loss, resulting in apparently healthy tissue bordering on exposed skeleton. In this study, the microenviron- mental condition and tissue structure of WS-affected tabular acroporid corals were assessed by O2 microelectrodes and histological techniques. The high spatial resolution of the microelectrode mea- surements enabled an evaluation of the extent of physiological changes at, and 2 cm away from, the WS border. Respiration of the coral host was decreased on the skeleton-tissue border but was compa- rable to that of healthy corals only 2 cm away from the border. Histological data, however, showed a decrease in mesogloea thickness on and 2 cm away from the WS border, which correlates with a pre- viously observed allocation of photoassimilates away from the WS border. We suggest that there are colony-wide negative effects of WS which affect only the host physiology and, as disparate etiologies are evident in WS, these must be distinguished through the utilization of a multiple tool approach.

Holocene sea-level record from corals: Reliability of paleodepth indicators at Ishigaki Island, Ryukyu Islands, Japan

Holocene sea-level change provides direct evidence of the melting of ice sheets; however, our understanding of the timing and course of such change is limited by a lack of information regarding environmental condition of corals. For example, Holocene sea-level curves are compiled based on water depths estimated from the occurrence of a small number of coral species, as species identification is difficult work. The error associated with this method of estimating sea level exceeds ± 2.5 m. In addition, there generally occurs a difference in the living-water depth of corals between high-energy reefs and low- to moderate-energy reefs. This difference in living-water depth also results in an error in reconstructed sea-level curves. In the present study, we analyzed drill core and recorded the vertical distribution of corals at the high-energy Ibaruma reef and low- to moderate-energy Fukido reef, Ishigaki Island, Ryukyu Islands, Japan. Analyses of corymbose Acropora ( A. digitifera), massive Goniastrea ( G. retiformis), massive Pocillopora ( P. verrucosa), massive Platygyra ( P. ryukyuensis), and other corals enables the accurate reconstruction of a sea-level curve because these species are distributed in a narrow range, with a weighted mean ( M w) error of between ± 0.5 and ± 2.5 m. These observation data from Ibaruma and Fukido reefs can be used to reconstruct Holocene sea-level curves based on drill core data from Ibaruma reef; however, the two reefs yield contrasting sea-level curves: the curve reconstructed based on data from Fukido reef is several meters deeper than that reconstructed based on data from Ibaruma reef. This discrepancy reflects the different energy levels of the two reefs (high-energy at Ibaruma reef and low- to moderate-energy at Fukido reef). Therefore, the accurate reconstruction of a Holocene sea-level curve requires the identification of species from drill core and observations of the vertical distribution of species at the present-day reef at a location close to the drilling site. The Holocene sea-level curve reconstructed based on drill core data from Ibaruma reef reveals a rapid sea-level rise of approximately 7.5 m kyr − 1 between 8000 and 6000 cal. years BP. The rate of sea-level rise decreased from 7.5 to 3.5 m kyr − 1 between 6000 and 5000 cal. years BP. A mid-Holocene highstand occurred at around 5000 cal. years BP, at a level of approximately 3 ± 2.5 m above the present mean sea level. The increase in ocean volume corresponding to this sea-level rise indicates that melting of the Antarctic ice sheet continued beyond 6000 cal. years BP, as most of the Northern Hemisphere ice sheets had melted by 6000 cal. years BP, resulting in sea levels similar to those of the present day.

Effects of coral bleaching on the feeding response of two species of coral-feeding fish

Coral bleaching is an increasingly prominent threat to coral reef ecosystems, not only to corals, but also to the many organisms that rely on coral for food and shelter. Coral-feeding fishes are negatively affected by coral loss caused by extensive bleaching, but it is unknown how feeding behaviour of most corallivorous fishes changes in response to coral bleaching. In this study, coral bleaching was experimentally induced in situ to examine the feeding response of two obligate corallivorous fish, Labrichthys unilineatus (Labridae) and Chaetodon baronessa (Chaetodontidae). Feeding rates were monitored before, during, and immediately after experimental bleaching of prey corals. L. unilineatus significantly increased its feeding on impacted corals during bleaching, but showed a steady decline in feeding once corals were fully bleached. Feeding response of L. unilineatus appears to parallel the expected stress-induced mucous production by bleaching colonies. In contrast, C. baronessa preferentially fed from healthy colonies over bleached colonies, although bleached colonies were consumed for five days following manipulation. Feeding by corallivorous fishes can play an important role in determining coral condition and mortality of corals following stress induced bleaching.

Coral Condition After Executing Large-Scale Coral Transplantation on Kuta Beach in Bali Island

The large-scale coral transplantation with applying asexual reproduction method has been implemented in the shallow lagoon at Kuta Beach in Bali Island of Indonesia. The monitoring and maintenance works after fixing coral fragments were continued for 1.5 years to observe the coral growth and survival conditions. The high survival rate and significant growth of transplanted corals were observed for branching and leaf type coral species which were brought from same coral reef area in comparison with other experiments in Japan. This is mainly caused by different environmental conditions from that in Japan; such as high water temperature with range of 24 to 30 degrees C, no disturbance by storm, inexistence of natural enemy, etc.

Coral health monitoring: linking coral colour and remote sensing techniques

Percent of living coral cover is an indicator commonly used to assess reef status. This study tested whether Coral Health Chart scores could be used as a proxy for spectral reflectance, which would provide a basis for mapping living coral cover at a finer scale (colour) using remote sensing techniques. A total of 1264 spectral reflectance measurements were taken in situ from corals representing the colour scores on the Coral Health Chart at Heron Island, Great Barrier Reef, Australia. Spectral analyses of reflectance magnitude showed that living coral could be classified with 72.41% overall accuracy into three colour categories: bleached, medium, and dark coral. First- and second-order derivative analyses did not improve the accuracy of classifying coral spectra into colour categories. Spectral analyses using only coral spectra from the genus Acropora also failed to improve classification results significantly, consistent with suggestions that coral reflectance is independent of taxonomy at the genus level. The results of this study provide a foundation for using the Coral Health Chart as a proxy to map and monitor living coral condition using remote sensing techniques.

Development of a coastal environment assessment system using coral recruitment

A new method for assessing coastal environments using the reproduction potential of corals has been developed and examined in situ. Six assessment racks were deployed before the full moon of May 2006 at three sites located around a river outlet in Nagura Bay, Ishigaki Is. and at one control location in Sekisei Lagoon. Each rack was equipped with two marine blocks (MB) containing 378 holes, two cases of coral settlement devices (CSDs), each containing 120 CSDs, and a water temperature logger. Assessment was based on recruitment of Acropora due to mass spawning. After 4 months of deployment, the surface of assessment racks showed apparent biofouling depending on sites mainly by algal settlement on the surfaces. Almost all the holes of the MBs were partly occupied, mainly by turf algae. Nagura Bay was thought likely to be an “unhealthy” coral reef due to runoff from land. However, our assessment showed that there were 0.85 corals per CSD in the Bay, compared with 0.51 in Sekisei Lagoon, indicating that coral larvae supply is not the cause of the unhealthy condition of corals in the Nagura Bay.

Evaluation of stony coral indicators for coral reef management

Colonies of reef-building stony corals at 57 stations around St. Croix, US Virgin Islands were characterized by species, size and percentage of living tissue. Taxonomic, biological and physical indicators of coral condition were derived from these measurements and assessed for their response to gradients of human disturbance—a requirement for indicators used in regulatory assessments under authority of the Clean Water Act. At the most intensely disturbed location, five of eight primary indicators were highly correlated with distance from the source of disturbance: Coral taxa richness, average colony size, the coefficient of variation of colony size, total topographic coral surface area, and live coral surface area. An additional set of exploratory indicators related to rarity, reproductive and spawning mode and taxonomic identity were also screened. The primary indicators demonstrated sufficient precision to detect levels of change that would be applicable in a regional-scale regulatory program.

Diving down the reefs? Intensive diving tourism threatens the reefs of the northern Red Sea

Intensive recreational SCUBA diving threatens coral reef ecosystems. The reefs at Dahab, South Sinai, Egypt, are among the world’s most dived (>30,000 dives y −1). We compared frequently dived sites to sites with no or little diving. Benthic communities and condition of corals were examined by the point intercept sampling method in the reef crest zone (3 m) and reef slope zone (12 m). Additionally, the abundance of corallivorous and herbivorous fish was estimated based on the visual census method. Sediments traps recorded the sedimentation rates caused by SCUBA divers. Zones subject to intensive SCUBA diving showed a significantly higher number of broken and damaged corals and significantly lower coral cover. Reef crest coral communities were significantly more affected than those of the reef slope: 95% of the broken colonies were branching ones. No effect of diving on the abundance of corallivorous and herbivorous fish was evident. At heavily used dive sites, diver-related sedimentation rates significantly decreased with increasing distance from the entrance, indicating poor buoyancy regulation at the initial phase of the dive. The results show a high negative impact of current SCUBA diving intensities on coral communities and coral condition. Corallivorous and herbivorous fishes are apparently not yet affected, but are endangered if coral cover decline continues. Reducing the number of dives per year, ecologically sustainable dive plans for individual sites, and reinforcing the environmental education of both dive guides and recreational divers are essential to conserve the ecological and the aesthetic qualities of these dive sites.

Coral fish condition in the waters of Pare-Pare Bay and Awerange Bay South Sulawesi

Observation on fish coral condition was conducted in the waters of Pare-Pare and Awerange Bay, South Sulawesi, on October and November 2004, using scuba diving set and under water writting tools. Monitoring of fish coral conditions were conducted in 7 m depths up to 100 m length of shore line were observed in four stations of diving, two stations in Pare-pare Bay and two stations in Awerange Bay using “sencus visual of Line Intercept Transect” method. The result showed that in the waters of Pare-Pare Bay were not found fish coral, just pelagic fish were found, meanwhile in the waters of Awerange Bay, fish coral found as much as 17 families and 46 specieses.© 2007 Jurusan Biologi FMIPA UNS SurakartaKey words: Coral fish condition, Pare-Pare Bay, Awerange Bay

Is proximity to land-based sources of coral stressors an appropriate measure of risk to coral reefs? An example from the Florida Reef Tract

Localized declines in coral condition are commonly linked to land-based sources of stressors that influence gradients of water quality, and the distance to sources of stressors is commonly used as a proxy for predicting the vulnerability and future status of reef resources. In this study, we evaluated explicitly whether proximity to shore and connections to coastal bays, two measures of potential land-based sources of disturbance, influence coral community and population structure, and the abundance, distribution, and condition of corals within patch reefs of the Florida Reef Tract. In the Florida Keys, long-term monitoring has documented significant differences in water quality along a cross-shelf gradient. Inshore habitats exhibit higher levels of nutrients (DIN and TP), TOC, turbidity, and light attenuation, and these levels decrease with increasing distance from shore and connections to tidal bays. In clear contrast to these patterns of water quality, corals on inshore patch reefs exhibited significantly higher coral cover, higher growth rates, and lower partial mortality rates than those documented in similar offshore habitats. Coral recruitment rates did not differ between inshore and offshore habitats. Corals on patch reefs closest to shore had well-spread population structures numerically dominated by intermediate to large colonies, while offshore populations showed narrower size-distributions that become increasingly positively skewed. Differences in size–structure of coral populations were attributed to faster growth and lower rates of partial mortality at inshore habitats. While the underlying causes for the favorable condition of inshore coral communities are not yet known, we hypothesize that the ability of corals to shift their trophic mode under adverse environmental conditions may be partly responsible for the observed patterns, as shown in other reef systems. This study, based on data collected from a uniform reef habitat type and coral species with diverse life-history and stress–response patterns from a heavily exploited reef system, showed that proximity to potential sources of stressors may not always prove an adequate proxy for assigning potential risks to reef health, and that hypothesized patterns of coral cover, population size–structure, growth, and mortality are not always directly related to water quality gradients.

Characterizing Coral Condition Using Estimates of Three-dimensional Colony Surface Area

Coral reefs provide shoreline protection, biological diversity, fishery harvests, and tourism, all values that stem from the physically-complex coral infrastructure. Stony corals (scleractinians) construct and maintain the reef through deposition of calcium carbonate. Therefore, assessment of coral reefs requires at least some measurement endpoints that reflect the biological and physical condition of stony corals. Most monitoring programs portray coral quantity as live coral cover, which is the two-dimensional proportion of coral surface to sea floor viewed from above (planar view). The absence of the third dimension, however, limits our ability to characterize coral reef value, physiology, health and sustainability. A three-dimensional (3D) approach more realistically characterizes coral structure available as community habitat and, when combined with estimates of live coral tissue, quantifies the amount of living coral available for photosynthesis, growth and reproduction. A rapid coral survey procedure that coupled 3D coral quantification with more traditional survey measurements was developed and tested in the field. The survey procedure relied on only three underwater observations--species identification, colony size, and proportion of live tissue--made on each colony in the transect. These observations generated a variety of metrics, including several based on 3D colony surface area, that are relevant to reef management.

Monitoring coral bleaching using a colour reference card

Assessment of the extent of coral bleaching has become an important part of studies that aim to understand the condition of coral reefs. In this study a reference card that uses differences in coral colour was developed as an inexpensive, rapid and non-invasive method for the assessment of bleaching. The card uses a 6 point brightness/saturation scale within four colour hues to record changes in bleaching state. Changes on the scale of 2 units or more reflect a change in symbiont density and chlorophyll a content, and therefore the bleaching state of the coral. When used by non-specialist observers in the field (here on an intertidal reef flat), there was an inter-observer error of I colour score. This technique improves on existing subjective assessment of bleaching state by visual observation and offers the potential for rapid, wide-area assessment of changing coral condition.

Characterizing Coral Condition Using Estimates of Three-Dimensional Colony Surface Area

Readily available nitrogen (N) sources such as ammonium nitrate with excessive irrigation present a potential hazard for the environment. The computer program Nitrate Leaching and Economic Analysis Package (NLEAP) is a mechanistic model developed for rapid site-specific estimates of nitrate-nitrogen (NO3-N) moving below the root zone in agricultural crops and potential impacts of NO3-N leaching into groundwater. In this study, the value of NLEAP was tested to simulate N uptake by crops and NO3-N leaching parameters in large lysimeters under the tomato crop. Three seedlings of tomato variety of H-2274 (Lycopersicum esculentum L.) were transplanted into each lysimeter. N fertilizer at the rate of 140 kg N ha(-1) was sidedressed in two split applications, the first half as ammonium sulphate and the second half as ammonium nitrate. The lysimeters were irrigated based on programs of C 0.75, 1.00, 1.25 and 1.50, C referring to class A-Pan evaporation coefficients. Parameters such as leaching index (LI), annual leaching risk potential (ALRP), N available for leaching (NAL), amount of NO3-N leached (NL) and amount of N taken up by the crops (NU) were estimated using the NLEAP computer model. To test the ability of model to simulate N uptake and NL, measured values were compared with simulated values. Significant correlations, R2 = 0.92 and P < 0.03 for the first year and R2 = 0.86 and P < 0.06 for the second year, were found between measured and simulated values for crop N consumption, indicating that the NLEAP model adequately described crop N uptake under the varied irrigation programs using an optimal N fertilization program for the experimental site. Significant correlations, R2 = 0.96 and P < 0.01 for the first year and R2 = 0.97 and P < 0.01 for the second year, were also found between measured and simulated values of NL, indicating that the NLEAP model also adequately predicted NL under the varied irrigation programs. Therefore, this computer model can be useful to estimate the NO3-N moving beyond the root zone under conditions in which the present experiment was carried out. Also, the NLEAP-estimated NAL values and other parameters can also be used to improve N management practices and N fertilizer recommendations that will help to decrease the adverse effect of N fertilizer on groundwater quality and farm profitability.

Increased mortality and photoinhibition in the symbiotic dinoflagellates of the Indo–Pacific coral Stylophora pistillata (Esper) after summer bleaching

Coral bleaching (the loss of symbiotic dinoflagellates from reef-building corals) is most frequently caused by high-light and temperature conditions. We exposed the explants of the hermatypic coral Stylophora pistillata to four combinations of light and temperature in late spring and also in late summer. During mid-summer, two NOAA bleaching warnings were issued for Heron Island reef (Southern Great Barrier Reef, Australia) when sea temperature exceeded the NOAA bleaching threshold, and a ‘mild’ (in terms of the whole coral community) bleaching event occurred, resulting in widespread S. pistillata bleaching and mortality. Symbiotic dinoflagellate biomass decreased by more than half from late spring to late summer (from 2.5×106 to 0.8×106 dinoflagellates cm2 coral tissue), and those dinoflagellates that remained after summer became photoinhibited more readily (dark-adapted F V : F M decreased to (0.3 compared with 0.4 in spring), and died in greater numbers (up to 17% dinoflagellate mortality compared with 5% in the spring) when exposed to artificially elevated light and temperature. Adding exogenous antioxidants (d-mannitol and l-ascorbic acid) to the water surrounding the coral had no clear effect on either photoinhibition or symbiont mortality. These data show that light and temperature stress cause mortality of the dinoflagellate symbionts within the coral, and that susceptibility to light and temperature stress is strongly related to coral condition. Photoinhibitory mechanisms are clearly involved, and will increase through a positive feedback mechanism: symbiont loss promotes further symbiont loss as the light microenvironment becomes progressively harsher.

The condition of coral reefs in South Florida (2000) using coral disease and bleaching as indicators

The destruction of coral reef habitats has occurred at unprecedented levels during the last three decades. Coral disease and bleaching in the Caribbean and South Florida have caused extensive coral mortality with limited recovery, often coral reefs are being replaced with turf algae. Acroporids were once dominant corals and have diminished to the state where they are being considered as endangered species. Our survey assessed the condition of reef corals throughout South Florida. A probability-based design produced unbiased estimates of the spatial extent of ecological condition, measured as the absence or presence and frequency or prevalence of coral diseases and bleaching intensity over large geographic regions. This approach allowed us to calculate a quantifiable level of uncertainty. Coral condition was estimated for 4100 hectares (ha) (or 41.0 km2) of coral reefs in South Florida, including reefs in the Florida Keys National Marine Sanctuary (FKNMS), New Grounds, Dry Tortugas National Park (DTNP), and Biscayne National Park (BNP). The absence or presence of coral disease, 'causal' coral bleaching, partial bleaching and coral paling were not good indicators of overall coral condition. It was more useful to report the prevalence of anomalies that indicated a compromised condition at both the population and community levels. For example, 79% of the area in South Florida had less than 6% of the coral colonies diseased, whereas only 2.2% (97.15 ha) of the sampled area had a maximum prevalence of 13% diseased coral colonies at any single location. The usefulness of 'causal bleaching' might be more important when considering the prevalence of each of the three different states at a single location. For example, paling was observed over the entire area, whereas bleaching and partial bleaching occurred at 19 and 41% of the area, respectively. An index for coral reef condition might integrate the prevalence and species affected by each bleaching state at individual locations. By establishing these baselines, future surveys can examine changes and trends in the spatial distribution of coral conditions in South Florida and able to score the reefs as to their health status.

A Rapid Method for Determining Lipid Fraction Ratios of Hard Corals under Varying Sediment and Light Regimes

Environmental Context.Monitoring the health of coral reef systems is vitally important to maintain and manage these threatened, complex and biodiverse natural ecosystems. Although total lipid content has been suggested as a potential index of coral condition, current methods of measurement are time consuming, technically challenging and expensive. These limitations have prohibited the application of coral lipid content as an impact-monitoring tool. The development of a practical and rapid method to determine lipid fraction ratios has the potential to lead towards an effective tool for coral reef monitoring. Abstract.Lipid content has been used as a measure of energetic status and condition in a number of fish and invertebrate species and can potentially be applied to hard corals. However, common methods for measuring lipid content are time consuming, technically challenging and expensive and these limitations have prohibited the application of lipid content as an impact-monitoring tool. To overcome these limitations, a rapid low-tech method for determining neutral to polar lipid ratios from hard coral tissue samples has been developed. This paper describes the development of the method together with a preliminary application of the technique carried out in a field study to determine whether the relative amounts of non-polar storage lipid to polar structural lipid may provide insight into the nutritional condition of individual coral colonies under differing environmental stresses. Variation in the lipid ratios of the hard coral Acropora nobilis, collected from the Montebello Islands off Western Australia, was correlated with local light and sediment regimes. This initial application of the method has demonstrated the viability of the technique, which subsequently has the potential to be applied in the analysis of a large number of samples as would be required in environmental monitoring.

Experimental responses to elevated water temperature in genotypes of the reef coral Pocillopora damicornis from upwelling and non-upwelling environments in Panama

The authors investigated the response to experimentally elevated water temperature in genotypes of Pocillopora damicornis from three coral reefs in the upwelling Gulf of Panama and four coral reefs in the non-upwelling Gulf of Chiriqui, Panamanian Pacific. Sea-surface temperature in the Gulf of Panama declines below 20 °C during seasonal upwelling, while in the thermally stable Gulf of Chiriqui, the temperature ranges from 27 to 29 °C. Genotypes of P. damicornis from the seven locations were determined by allozyme electrophoresis. The most abundant genotype at each location was selected for a thermal tolerance experiment where corals were exposed to water temperature of 30 °C (1 °C above ambient) for 43 days. Four site coral genotypes can be uniquely differentiated by the GPI locus, two by the LGG-2 locus, and two by a combination of the MDH-1, LGG-2, and LTY-3 loci. A visual assessment of the coral condition after exposure to an elevated temperature showed that corals from localities in the non-upwelling environment retained a normal to slightly pale appearance, while corals from the upwelling environment bleached and their polyps were mostly retracted. A two-way ANOVA confirmed that corals were significantly affected by water temperature and locality. The zooxanthellae were also significantly affected by the interaction of elevated temperature and locality of the corals. Mean zooxanthellae density decreased by 25 and 55%, respectively, in experimentally heated corals from the non-upwelling and upwelling environments. Low concentrations of photosynthetic pigments per live area of the corals were the norm in corals under elevated temperature. The mean concentration of chlorophyll a per live area of the corals was reduced by 17 and 49%, respectively, in heated corals from the non-upwelling and upwelling sites. Coral genotypes from the upwelling Gulf of Panama demonstrated higher vulnerability to thermal stress than coral genotypes from the non-upwelling Gulf of Chiriqui. However, the latter showed greater differences in their responses. Thus, even at small geographic scales, corals can display different levels of tolerance to thermal stress. The difference in thermal tolerance between corals from upwelling and non-upwelling environments is concomitant with greater genetic differences in experimental corals from the thermally stable Gulf of Chiriqui compared with corals from the upwelling Gulf of Panama.