Search

SUMMARY This study describes the effects of temperature on the respiration of brooded larvae of scleractinian corals, and evaluates the implications of these effects relative to seawater temperature when peak larval release occurs. Respiration rates of larvae from Pocillopora damicornis, Seriatopora hystrix and Stylophora pistillata were quantified in darkness as oxygen uptake during 1–3 h exposures to five temperatures between 26.4 and 29.6°C. To assess the biological significance of these experiments, the temperature of the seawater into which larvae of P. damicornis and S. hystrix were released was measured for 32–34 months over 5 years between 2003 and 2008. Mean respiration varied from 0.029 to 0.116 nmol O2 larva–1 min–1, and was related parabolically to temperature with a positive threshold at 28.0°C. The temperature coefficients (Q10) for the ascending portion of these relationships (Q10=15–76) indicate that the temperature dependency is stronger than can be explained by kinetics alone, and probably reflects behavioral and developmental effects. Larval release occurred year-round in synchrony with the lunar periodicity when seawater temperature ranged from 21.8 to 30.7°C, and more than half of the sampled larvae were released at 27.5–28.9°C. The coincidence on the temperature scale of peak larval release with the thermal threshold for respiration suggests that high metabolic rates have selective value for pelagic coral larvae. The large and rapid effects of temperature on larval respiration have implications for studies of the effects of climate change on coral reproduction, particularly when seawater temperature exceeds ∼28°C, when our results predict that larval respiration will be greatly reduced.

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. © 2011 Adam et al.

Evaluating the response of organisms to stress assumes that functional benchmarks are available against which the response can be gauged, but this expectation remains unfulfilled for many taxa. As a result, attempts to describe the organismic effects of environmental degrada- tion and physiological stress can prove misleading. Func- tional benchmarks and the effects of stress are particularly germane to coral reefs that globally are exposed to sig- nificant environmental challenges, and in this study, we compiled data on scleractinian corals to describe a refer- ence against which stress responses can be gauged. Based on this construct, we tested the veracity of well-established contrasts--involving differences in physiological function among depths and families--to evaluate the capacity of available data to support synthetic analyses. Our analysis used 126 papers describing 37 genera, and at least 73 species, and described 13 traits, first independent of depth, and second, by depth. Data appropriate for these analyses were so sparse that depth- and family-level effects were inconspicuous, although the depth contrast revealed a decline in dark respiration and an increase in calcification (both normalized to area) in deeper water. Our analyses of scleractinian literature revealed limitations of the data available for synthetic analyses, as well for describing functional benchmarks within this taxon. We attribute some of these effects to differences in the physical envi- ronment under which measurements were made, and sus- pect that such problems are commonplace for other taxa. Dynamic Energy Budget (DEB) models provide one means to overcome some of these problems, and they can be used for any taxon to quantitatively summarize data for com- parative analyses of stressor responses. The suitability of these models is illustrated for scleractinian corals by pre- dicting from first principles the ratio of Symbiodinium to holobiont carbon and the respiration.

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.

In this paper we develop and investigate a dynamic energy budget (DEB) model describing the syntrophic symbiotic relationship between a heterotrophic host and an internal photoautotrophic symbiont. The model specifies the flows of matter and energy among host, symbiont and environment with minimal complexity and uses the concept of synthesizing units to describe smoothly the assimilation of multiple limiting factors, in particular inorganic carbon and nitrogen, and irradiance. The model has two passive regulation mechanisms: the symbiont shares only photosynthate that it cannot use itself, and the host delivers only excess nutrients to the symbiont. With parameter values plausible for scleractinian corals, we show that these two regulation mechanisms suffice to obtain a stable symbiotic relationship under constant ambient conditions, provided those conditions support sustenance of host and symbiont. Furthermore, the symbiont density in the host varies relatively little as a function of ambient food density, inorganic nitrogen and irradiance. This symbiont density tends to increase with light deprivation or nitrogen enrichment, either directly or via food. We also investigate the relative benefit each partner derives from the relationship and conclude that this relationship may shift from mutualism to parasitism as environmental conditions change. © 2009 Elsevier Ltd. All rights reserved.

In this study, two factorial experiments were used to investigate the role of tissue age in affecting the phenotypic expression of calcification in scleractinian corals. Both experiments tested whether calcification was altered by tissue age and whether corals of different ages exploit plasticity to differing degrees by altering calcification rates under new environmental conditions. To isolate age and size effects, branches of the Caribbean coral Madracis mirabilis were broken into a distal portion that was functionally young and a proximal portion that was functionally old. Fragments were transplanted from a deep (17 m) to a shallow (9 m) site in a Jamaican lagoon to test whether age affected the plasticity of calcification. Both experiments demonstrated that calcification scaled isometrically in the two age groups, and although scaling exponents were indistinguishable statistically among ages, young fragments calcified faster than old fragments. Thus, the effect of age on calcification rate was absolute and independent of size. However, the interactive effect of age and depth was not significant, demonstrating that ability to alter calcification rate (i.e., the extent of phenotypic plasticity for this trait) was unaffected by age. Together, these patterns are consistent with the hypothesis that the proximal modules (i.e., polyps) of M. mirabilis are subject to physiological senescence, as has been reported for other clonal organisms, including algae, fungi, plants, bryozoans, ascidians, and other cnidarians.

The recruitment and survival of juvenile corals is central to the maintenance of coral reef communities and the repopulation of denuded reef substrata. Although it is widely accepted that the mortality of scleractinians is inversely proportional to size, the biotic and abiotic factors that drive this trend remain unclear. Here we measure the mortality of corals on the reefs of St. John (U.S. Virgin Islands) to demonstrate that small corals are more likely to die than their larger counterparts, and we explore whether the photophysiological performance of juveniles in two size classes can provide some insight into why smaller corals are so vulnerable. To evaluate photophysiological performance, we examined chlorophyll fluorescence in two size classes (mean diameters 15 mm and 45 mm) of juvenile colonies of Porites astreoides exposed for short periods to ambient and elevated temperatures. Our results show that the photophysiology of these size classes differs under ambient conditions, with dark-adapted quantum yield (Fv /Fm) being significantly higher in smaller compared to bigger juveniles. As expected, the photophysiology of both size classes is negatively impacted by thermal stress, and although size-related trends are evident in our data, the interaction between size and temperature is not statistically significant. Thus, while there is size dependency in the photophysiological performance of juvenile colonies of P. astreoides, the link between this aspect of scleractinian biology and the higher mortality of small juvenile corals in the face of high thermal stress remains unclear. As a context for this study, we draw on mortality data for different size classes of corals at five sites on the shallow reefs of St. John. Between 1996 and 2002, the annual mortality of all juvenile corals 20 mm in diameter was 2-fold higher than for corals of 21‐ 40 mm in diameter (Fig.

Ocean acidification (OA) and its associated decline in calcium carbonate saturation states is one of the major threats that tropical coral reefs face this century. Previous studies of the effect of OA on coral reef calcifiers have described a wide variety of outcomes for studies using comparable partial pressure of CO 2 ( p CO 2 ) ranges, suggesting that key questions remain unresolved. One unresolved hypothesis posits that heterogeneity in the response of reef calcifiers to high p CO 2 is a result of regional-scale variation in the responses to OA. To test this hypothesis, we incubated two coral taxa ( Pocillopora damicornis and massive Porites ) and two calcified algae ( Porolithon onkodes and Halimeda macroloba ) under 400, 700 and 1000 μatm p CO 2 levels in experiments in Moorea (French Polynesia), Hawaii (USA) and Okinawa (Japan), where environmental conditions differ. Both corals and H. macroloba were insensitive to OA at all three locations, while the effects of OA on P. onkodes were location-specific. In Moorea and Hawaii, calcification of P. onkodes was depressed by high p CO 2 , but for specimens in Okinawa, there was no effect of OA. Using a study of large geographical scale, we show that resistance to OA of some reef species is a constitutive character expressed across the Pacific.

After several decades of disturbance, many coral reefs in the Caribbean are dominated by macroalgae. One process affecting this transition is coral-macroalgal competition, yet few studies have addressed the mechanisms involved. In this study, we investigated competition between the tall and bushy macroalga Sargassum hystrix (J. Agardh) and the branching coral Porites porites (Pallas) on a shallow reef in Jamaica. Experiments were designed to expose coral branches to different treatments to test the role of shading and abrasion by Sargassum on coral growth and polyp expansion. Corals exposed to Sargassum grew significantly more slowly (80% reduction) than controls, but this effect was absent when corals were caged to prevent physical contact with macroalgae. Light levels were reduced in both the algal and cage treatments, but shading apparently had little effect on the growth of corals in cages. Short-term measurements of integrated net water flow did not detect variation among treatments. In algal-mimic treatments, where clear plastic strips could touch but not shade the corals, growth rates were 25% lower than controls, but this effect was not statistically significant. Thus, the growth of corals in contact with Sargassum was reduced by abrasion and, to a lesser extent, by factors unique to living macroalgae. Analysis of polyp expansion showed that polyps were more frequently retracted when corals were in contact with macroalgae or algal-mimics compared to controls or cage treatment; the frequency of polyp contraction was correlated positively with growth. Together, these results suggest that abrasion-mediated polyp retraction is one of the primary mechanisms of competition utilized by tall (ca. 17 cm) macroalgae against scleractinian corals.

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.

Central to evaluating the effects of ocean acidification (OA) on coral reefs is understanding how calcification is affected by the dissolution of CO2in 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 coralPorites rusand the algaHydrolithon 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 ofP. rus, whereas [HCO3−] mainly affected calcification in the light. Both [CO32−] and [HCO3−] had a significant effect on the calcification ofH. 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.

Corals face unique challenges in their early life stages, as their larvae lack tentacles to capture particulates to meet metabolic demands. Instead, they must meet these costs from food reserves or alternative modes of nutrition such as dissolved organic material or, when they contain Symbiodinium, autotrophy (Edmunds et al. 2001). Once settled, rapid metamorphosis and development of tentacles are advantageous, because tentacles facilitate particle capture to augment the supply of energy and nutrients necessary for polyp growth. However, it is unknown how early in their development corals begin to capture and ingest food.

Tropical reef corals are ecologically important examples of mutualistic symbioses whose success is defined by the interwoven biologies of their symbiotic partners. These associations are exquisitely regulated, yet the equilibrium is sensitive to environmental disturbances, which cause a breakdown in symbiotic communication, loss of algae from the host, concomitant paling of coral coloration known as coral bleaching, and, if the conditions persist, death of the coral. Faced with the prospect of catastrophic coral mortality associated with global warming and related environmental shifts, researchers have focused their efforts on coral bleaching; although significant progress has been made in this area, understanding of the basic biology of these associations remains poor. Here we discuss several issues that have potentially contributed to this knowledge gap and conclude that without a sound understanding of the basic biology of these important symbioses, it will be very difficult to elucidate the m...

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