Peter J. Edmunds

Recovery of Diadema antillarum reduces macroalgal cover and increases abundance of juvenile corals on a Caribbean reef

The transition of many Caribbean reefs from coral to macroalgal dominance has been a prominent issue in coral reef ecology for more than 20 years. Alternative stable state theory predicts that these changes are reversible but, to date, there is little indication of this having occurred. Here we present evidence of the initiation of such a reversal in Jamaica, where shallow reefs at five sites along 8 km of coastline now are characterized by a sea urchin-grazed zone with a mean width of 60 m. In comparison to the seaward algal zone, macroalgae are rare in the urchin zone, where the density of Diadema antillarum is 10 times higher and the density of juvenile corals is up to 11 times higher. These densities are close to those recorded in the late 1970s and early 1980s and are in striking contrast to the decade-long recruitment failure for both Diadema and scleractinians. If these trends continue and expand spatially, reefs throughout the Caribbean may again become dominated by corals and algal turf.

An energy budget for Porites porites (Scleractinia)

An energy budget for Porites porites (Pallas) was determined for specimens from 10 m depth on the Fore Reef of Discovery Bay, Jamaica, between July 1984 and July 1985. Evidence for habitual zooplankton ingestion was not obtained, and P. porites appears to be largely autotrophic. Out of the daily photosynthetically fixed energy, 26% is used for animal respiration and growth, 22% for zooxanthellae respiration and growth, and <1% for colony reproduction as mature planulae; 45% remains unaccounted for. Colony respiration, net photosynthesis, colony skeleton and tissue growth, zooplankton ingestion, reproductive effort and energy content of tissues were measured. Energy loss as continuous mucus secretion was not detected, but may occur by an alternative route via mucus tunics, which occur periodically in situ and in the laboratory. The energy budget suggests that a considerable excess of photosynthetically fixed energy is produced on an ideal sunny day at 10 m depth. This surplus may be required for periodic rather than continuous energy demands, or may be essential to survive “less-than-ideal” days, when net photosynthetic input is reduced.

THE DEMOGRAPHICS OF A 15-YEAR DECLINE IN COVER OF THE CARIBBEAN REEF CORAL MONTASTRAEA ANNULARIS

On Caribbean reefs, a striking trend of the last 25 years has been the decline in cover of the framework-building coral Montastraea annularis, a species that has dominated reefs throughout the region for millennia. Clearly, such losses are important ecologically, but to evaluate their significance fully, they need to be placed in the context of the proximal causes and balanced against the potential for gains in cover through growth and recruitment. In this study, a population of M. annularis in St. John, U.S. Virgin Islands, was censused annually from 1988 to 2003 to quantify coral cover and construct a size-based demographic model. The model was developed to explore the mechanisms of change in coral cover and to ascertain likely trajectories for future population growth. Over the study period, the cover of M. annularis declined from 41% in 1988, to 12% by 1999 (a 72% decline) but remained unchanged statistically for the last five years of the study. Between 1988 and 2003, colony abundances declined by 57...

Recurrent disturbances, recovery trajectories, and resilience of coral assemblages on a South Central Pacific reef

Coral reefs are increasingly threatened by various disturbances, and a critical challenge is to determine their ability for resistance and resilience. Coral assemblages in Moorea, French Polynesia, have been impacted by multiple disturbances (one cyclone and four bleaching events between 1991 and 2006). The 1991 disturbances caused large declines in coral cover (~51% to ~22%), and subsequent colonization by turf algae (~16% to ~49%), but this phase-shift from coral to algal dominance has not persisted. Instead, the composition of the coral community changed following the disturbances, notably favoring an increased cover of Porites, reduced cover of Montipora and Pocillopora, and a full return of Acropora; in this form, the reef returned to pre-disturbance coral cover within a decade. Thus, this coral assemblage is characterized by resilience in terms of coral cover, but plasticity in terms of community composition.

Extent and effect of Black Band Disease on a Caribbean reef

The effect of Black Band Disease (BBD) among colonies ofMontastrea annularis, M. cavernosa, Diploria strigosa, D. labryinthiformis, S. siderea andColpophyllia natans was determined at 7 shallow locations in the Virgin Islands. Between September 1988 and November 1988, 0.2% of 9204 colonies of these species were infected with BBD in 6908 m2 of reef at 22 randomly chosen areas. Infected colonies were not clumped suggesting that the disease is not highly infectious between colonies. BBD infection rates in areas surveyed 4 times between August 1988 and September 1989 in Greater Lameshur Bay, St. John, USVI, were significantly lower in winter compared to summer. BBDs were found on 5.5% of the colonies ofD. strigosa in Fall 1988, and 7 out of 12 infected colonies lost >75% of their tissue in 6 months. Low level, chronic BBD infections could convert 3.9% of the living cover ofD.strigosa to free space per year, thereby creating substrata for successional processes.

CLONAL VARIATION FOR PHENOTYPIC PLASTICITY IN THE CORAL MADRACIS MIRABILIS

Morphological plasticity is common among clonal organisms, including scleractinian corals, yet the role of phenotypic plasticity in coral ecology and evolution is largely unexplored. Additionally, it is unclear how much variation in plastic responses exists among individuals, populations, and species, and thus how much potential there is for natural selection to act on coral reaction norms. In the branching coral Madracis mi- rabilis, corallite architecture and density, branch diameter and spacing, and overall aggregate morphology all vary among environments. To examine the role of phenotypic plasticity in generating these patterns, clonal replicates of five genotypes of M. mirabilis were trans- planted from each of two source populations into four treatment environments on the north coast of Jamaica. Flow rate, sedimentation, irradiance, water temperature, and salinity all varied among these environments. DNA fingerprinting was used to ensure that the 10 transplanted genotypes were genetically distinct. Six morphological traits (intersepta area, septa length, columella area, corallite area, corallite spacing, and branch tip diameter) were measured after transplantation to determine whether they were altered in response to en- vironmental conditions. Because these traits were correlated, principal components analysis was used to define new, uncorrelated traits for analysis. Four of the five corallite traits and branch diameter were significantly affected by the environment, demonstrating that mor- phological variation among environments in M. mirabilis is due in large part to phenotypic plasticity. No difference was detected between the two source populations in the magnitude or direction of their plastic responses, but there was substantial variation among genotypes (genotype 3 environment interaction). Many of the phenotypic changes of both populations resulted in the transplants becoming morphologically similar to resident conspecifics in each treatment environment. Genotypes from both populations were able to maintain similar growth rates under diverse environmental conditions. Such morphological convergence by phenotypic plasticity may expand the ecological range of this species by enabling genotypes to tolerate spatially and temporally variable environments.

Herbivory, Connectivity, and Ecosystem Resilience: Response of a Coral Reef to a Large-Scale Perturbation

Coral reefs world-wide are threatened by escalating local and global impacts, and some impacted reefs have shifted from coral dominance to a state dominated by macroalgae. Therefore, there is a growing need to understand the processes that affect the capacity of these ecosystems to return to coral dominance following disturbances, including those that prevent the establishment of persistent stands of macroalgae. Unlike many reefs in the Caribbean, over the last several decades, reefs around the Indo-Pacific island of Moorea, French Polynesia have consistently returned to coral dominance following major perturbations without shifting to a macroalgae-dominated state. Here, we present evidence of a rapid increase in populations of herbivorous fishes following the most recent perturbation, and show that grazing by these herbivores has prevented the establishment of macroalgae following near complete loss of coral on offshore reefs. Importantly, we found the positive response of herbivorous fishes to increased benthic primary productivity associated with coral loss was driven largely by parrotfishes that initially recruit to stable nursery habitat within the lagoons before moving to offshore reefs later in life. These results underscore the importance of connectivity between the lagoon and offshore reefs for preventing the establishment of macroalgae following disturbances, and indicate that protecting nearshore nursery habitat of herbivorous fishes is critical for maintaining reef resilience.

Evidence that reef-wide patterns of coral bleaching may be the result of the distribution of bleaching-susceptible clones

The hypothesis that intraspecific variation in coral bleaching is a result of the distribution of bleaching-susceptible clonal genotypes (genets) was addressed using photoquadrats recorded during the 1987 Caribbean bleaching event on a reef dominated by Montastraea annularis (Morphotype I), together with manipulative experiments with Porites porites. Nearest-neighbor analysis showed that bleached colonies (ramets) of M. annularis at 10 m depth had a high probability (0.80) of having a nearest bleached neighbor of the same genet rather than a bleached ramet of a different genet. Furthermore, the frequency distributions of bleached ramets of M. annularis in the photoquadrats was significantly different from a Poisson distribution, suggesting that bleached ramets were aggregated on the reef. Manipulative experiments with P. porites from 15 m depth showed that some genets were more susceptible to thermal bleaching than others, since three genets had significantly different rates of zooxanthellae loss when exposed to elevated temperatures in tanks receiving irradiances similar to those found in situ. These results suggest that the in situ patchy distribution of bleached ramets could correspond to the distribution of certain genets, and that adjacent genets can exhibit sufficiently different phenotypes to account for intraspecific variation in bleaching. Further studies of genet-specific coral bleaching may provide valuable insights into the causes and consequences of bleaching.

Coral reef calcifiers buffer their response to ocean acidification using both bicarbonate and carbonate.

Central to evaluating the effects of ocean acidification (OA) on coral reefs is understanding how calcification is affected by the dissolution of CO2 in sea water, which causes declines in carbonate ion concentration [CO32−] and increases in bicarbonate ion concentration [HCO3−]. To address this topic, we manipulated [CO32−] and [HCO3−] to test the effects on calcification of the coral Porites rus and the alga Hydrolithon onkodes, measured from the start to the end of a 15-day incubation, as well as in the day and night. [CO32−] played a significant role in light and dark calcification of P. rus, whereas [HCO3−] mainly affected calcification in the light. Both [CO32−] and [HCO3−] had a significant effect on the calcification of H. onkodes, but the strongest relationship was found with [CO32−]. Our results show that the negative effect of declining [CO32−] on the calcification of corals and algae can be partly mitigated by the use of HCO3− for calcification and perhaps photosynthesis. These results add empirical support to two conceptual models that can form a template for further research to account for the calcification response of corals and crustose coralline algae to OA.

An energy budget for Porites porites (Scleractinia), growing in a stressed environment

An energy budget was determined for the coral Porites porites living in a stressed environment for comparison of the energy inputs and expenditure with those of the same species living in an adjacent clear water fore reef environment. The stressed site was characterised by higher sedimentation and lower irradiances than at the fore reef site. Zooplankton ingestion was found to be an insignificant component of the energy intake: the coral is fully autotrophic under stress conditions. The integrated 24 h rate of photosynthetic energy production on a clear sunny day was 20% higher for stressed corals compared to fore reef corals. This was largely the result of photoadaptation which resulted in increased values for α and decreased values for Ik in the hyperbolic tangent function equation for the photosynthesis versus irradiance curve. The energy investment in growth of animal tissue was lower in stressed corals. The percentage translocation of photosynthase to the animal tissue remained at about 78%, but the respiration rate of the animal tissue was reduced by 3 fold. These data combined with the high rate of photosynthetic production predict a net daily energy surplus of 67% in stressed corals compared with the 45% surplus in unstressed corals. Scope for growth is reduced under stress conditions.