Sensitivity of Calcification to Thermal Stress Varies among Genera of Massive Reef-Building Corals

Reductions in calcification in reef-building corals occur when thermal conditions are suboptimal, but it is unclear how they vary between genera in response to the same thermal stress event. Using densitometry techniques, we investigate reductions in the calcification rate of massive Porites spp. from the Great Barrier Reef (GBR), and P. astreoides, Montastraea faveolata, and M. franksi from the Mesoamerican Barrier Reef (MBR), and correlate them to thermal stress associated with ocean warming. Results show that Porites spp. are more sensitive to increasing temperature than Montastraea, with calcification rates decreasing by 0.40 g cm−2 year−1 in Porites spp. and 0.12 g cm−2 year−1 in Montastraea spp. for each 1°C increase. Under similar warming trends, the predicted calcification rates at 2100 are close to zero in Porites spp. and reduced by 40% in Montastraea spp. However, these predictions do not account for ocean acidification. Although yearly mean aragonite saturation (Ωar) at MBR sites has recently decreased, only P. astreoides at Chinchorro showed a reduction in calcification. In corals at the other sites calcification did not change, indicating there was no widespread effect of Ωar changes on coral calcification rate in the MBR. Even in the absence of ocean acidification, differential reductions in calcification between Porites spp. and Montastraea spp. associated with warming might be expected to have significant ecological repercussions. For instance, Porites spp. invest increased calcification in extension, and under warming scenarios it may reduce their ability to compete for space. As a consequence, shifts in taxonomic composition would be expected in Indo-Pacific reefs with uncertain repercussions for biodiversity. By contrast, Montastraea spp. use their increased calcification resources to construct denser skeletons. Reductions in calcification would therefore make them more susceptible to both physical and biological breakdown, seriously affecting ecosystem function in Atlantic reefs

Growth characteristics of skeletons of Montastraea annularis (Cnidaria: Scleractinia) from the northwest coast of Cuba

Growth characteristics (extension rate, density, and calcification rate) were determined using annual growth bands in skeletons of the reef-building coral Montastraea annularis, collected at 10 m depth on the northwest coast of Cuba. X-radiography contact prints revealed that the high-density band is formed during the warmest months of the year. Growth characteristics obtained were within the range of values presented by other authors for M. annularis in reefs distributed throughout the Atlantic. The relationships among the measured growth characteristics were similar to those previously described by other authors. The relationship found between calcification rate and sea surface temperature gradient in the Caribbean suggests that populations of M. annularis on the northwest coast of Cuba are related to populations of this species from the Caribbean and not to those from the Gulf of Mexico.

Relationships between Manicina areolata (Cnidaria : Scleractinia), Thalassia testudinum (Anthophyta) and Neogoniolithon sp (Rhodophyta)

The free-living coral Manicina areolata, the seagrass Thalassia testudinum, and the coralline algae Neogoniolithon sp, co-occur in the reef lagoon of Xahuayxol, Quintana Roo, in the Mexican Caribbean. The distribution and abundance of these organisms was measured. In order to study why the coral was distributed only within the medium-density stands of T. testudinum, but not in the high- or low- density stands of the seagrass, 3 size classes of M. areolata were transplanted into 3 naturally occurring seagrass densities. Mortality, displacement, righting reaction, zooxanthellae, mitotic index, and chLorophyll a were evaluated for the transplanted colonies. High mortality of M. areolata was recorded in the low-density zone of T. testudinum, attributable to siltation and predation, whereas in the high-density zone of this seagrass, the coral was under stress, as indicated by a lowered zooxanthellae density. The fragile, arborescent algae Neogoniolithon sp. was found distributed only within the medium-density zone of T. testudinum, and M. areolata selectively recruited onto that algae. Experiments in which the coral and algae were separated in the medium-density seagrass zone demonstrated that Neogoniolithon sp. offers M, areolata adaptive and ecological advantages: its survivorship was significantly higher when attached to the algae than when this substrate was not available. Because of the natural distribution of Neogoniolithon sp., the coral did not recruit in zones that would cause it stress, or even death. M, areolata and Neogoniolithon sp, eventually separate because of the increase in size (and weight) of the coral, and the fragility of the algae. Thus, the distribution of Neogoniolithon sp. explained the distribution of M, areolata instead of the high negative correlation found between the density of T. testudinum and the coral

Regional-scale dominance of non-framework building corals on Caribbean reefs affects carbonate production and future reef growth

publication-status: Publishedtypes: ArticleThis is the author's post-print version of an article published in Global Change Biology, Vol. 21, issue 3 pp. 1153 – 1164 Copyright © Wiley-Blackwell 2015. The definitive version is available at www3.interscience.wiley.comCoral cover on Caribbean reefs has declined rapidly since the early 1980's. Diseases have been a major driver, decimating communities of framework building Acropora and Orbicella coral species, and reportedly leading to the emergence of novel coral assemblages often dominated by domed and plating species of the genera Agaricia, Porites and Siderastrea. These corals were not historically important Caribbean framework builders, and typically have much smaller stature and lower calcification rates, fuelling concerns over reef carbonate production and growth potential. Using data from 75 reefs from across the Caribbean we quantify: (i) the magnitude of non-framework building coral dominance throughout the region and (ii) the contribution of these corals to contemporary carbonate production. Our data show that live coral cover averages 18.2% across our sites and coral carbonate production 4.1 kg CaCO3 m−2 yr−1. However, non-framework building coral species dominate and are major carbonate producers at a high proportion of sites; they are more abundant than Acropora and Orbicella at 73% of sites; contribute an average 68% of the carbonate produced; and produce more than half the carbonate at 79% of sites. Coral cover and carbonate production rate are strongly correlated but, as relative abundance of non-framework building corals increases, average carbonate production rates decline. Consequently, the use of coral cover as a predictor of carbonate budget status, without species level production rate data, needs to be treated with caution. Our findings provide compelling evidence for the Caribbean-wide dominance of non-framework building coral taxa, and that these species are now major regional carbonate producers. However, because these species typically have lower calcification rates, continued transitions to states dominated by non-framework building coral species will further reduce carbonate production rates below ‘predecline’ levels, resulting in shifts towards negative carbonate budget states and reducing reef growth potential.Trust International Research NetworkNational Geographic Society Researc