In the Campeche Knolls, in the southern Gulf of Mexico, lava-like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level. Chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt, which chilled and contracted after discharge. The site also includes oil seeps, gas hydrate deposits, locally anoxic sediments, and slabs of authigenic carbonate. Asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the Gulf of Mexico.

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 (Ω_ar) 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 Ω_ar 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.