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

Biogeography of the ahermatypic corals (Scleractinia) of the Mexican Pacific

 Stony corals have distinct ecological characteristics that are reflected in their ability to build reefs (hermatypic) or not (ahermatypic). The objective of this work was to systematize and analyze the literature and museum records of ahermatypic species of the west coast of Mexico, in order to determine their main patterns of geographical distribution. A total of 37 species were found, consisting of 25 genera and 8 families, a richness on the west coast of America comparable only to that found on the Galapagos Islands and adjacent zones. Most ahermatypic corals have a wide distribution and the Mexican fauna is dominated by eastern Pacific (67%), cosmopolitan (14%) and Indo-Pacific (8%) species. These percentages are noticeably different from the ones recorded for hermatypic corals (almost all of Indo- Pacific origin), and may indicate that the processes of extinction and recolonization undergone by the reef corals after the Pleistocene did not influence the coral species of deeper waters as much. Ordination analyses revealed that the study area is divided into three parts: the west coast of the Baja California peninsula (23º to 32ºN), the Gulf of California (23º to 31ºN) and the tropical Mexican Pacific (14º to 22ºN), a similar arrangement to that shown by other typical shallow-water groups. A positive correlation between species richness and mean sea surface temperature was found, as well as negative correlations among species richness, latitude and the annual surface temperature range, which explains why there was a higher species richness in the southern Mexican Pacific than in the rest of the zones analyzed