Most corals worldwide are broadcast spawners that rely on synchronous gamete release for successful fertilization. Spawning synchrony may also decrease the probability of heterospecific fertilization that may produce maladaptive hybrids. Despite the importance of reproductive timing, researchers have only recently begun to collect spawning data across coral species in the Caribbean, but these data remain to be analyzed. This study investigates interannual, seasonal, and environmental patterns that may influence Caribbean scleractinian spawning times. The number of spawning observations varies widely among location and species. Most spawning observations were collected in Florida, Curaçao, and Flower Garden Banks National Marine Sanctuary. Acropora palmata, A. cervicornis, and Orbicella species were the most documented. The Orbicella spp. were very consistent for spawning day annually, while the acroporids were less reliable. However, the acroporids were more consistent for spawning time in minutes after sunset between years. Season and moon cycles were obvious proximate cues for spawning, but a strong influence from wind and tides was absent. Acropora cervicornis was the only species in this study which spawning was significantly affected by water temperature. For some scleractinians, the day of spawning was significantly affected by mass bleaching events; spawning could occur on earlier days than in previous years for up to two years after the event. This study highlights existing data gaps for Pseudodiploria clivosa, A. prolifera and Siderastrea siderea. Documenting spawning patterns is crucial to better understand the potential impacts of future threats on the already imperiled Caribbean corals at risk from reproductive failure.

Ocean warming and acidification pose major threats to coral reef organisms. It is unknown how the early life history stages of Atlantic corals cope with the combined effects of these two global environmental stressors. Here, I investigate how these stressors influence the fertilization success, larval survivorship, and settlement of the threatened Atlantic coral, Orbicella faveolata. Gametes from O. faveolata were subjected to a factorial combination of present and future scenarios of oceanic temperatures (28.5° C and 30° C) and pH (8.2 and 8.0) predicted to occur by 2050. Results indicate that treatment type did not significantly affect fertilization success. Elevated temperature caused complete larval mortality and inhibited the settlement of O. faveolata. Interestingly, these negative effects of high temperature were partially mitigated when combined with ocean acidification. Overall, both the larval survivorship and settlement in the combined treatment was reduced to approximately half when compared to ambient treatment. Although ocean acidification may partially mitigate the negative effects of ocean warming during the larval stage, the overall reduced survival and settlement of larvae under future oceanic conditions, coupled to reduced calcification in adults, portends devastating effects on the health of this threatened species.

Coral reefs are one of the most economically important ecosystems on the planet. Despite their great contribution to the world economy, anthropogenic influence via carbon dioxide emissions is leading to unprecedented changes with concerns about subsequent negative impacts on reefs. Surface ocean pH has dropped 0.1 units in the past century; in spite of this rapid shift in oceanic chemistry, it is unclear if individual species or life stages of Caribbean stony corals will be more sensitive to ocean acidification (OA). Examined is the relationship between CO2-induced seawater acidification, net calcification, photosynthesis, and respiration in three model Caribbean coral species: Orbicella faveolata, Montastraea cavernosa, and Dichocoenia stokesi, under near ambient (465 ± 5.52 ppm), and high (1451 ± 6.51 ppm) CO2 conditions. A species specific response was observed for net calcification; D. stokesi and M. cavernosa displayed a significant reduction in CaCO3 secreted under OA conditions, while O. faveolata fragments showed no significant difference. At the cellular level, transmission electron micrographs verified that all species and treatments were actively calcifying. Skeletal crystals nucleated by O. faveolata in the high CO2 treatments were statistically longer relative to controls. These results suggest that the addition of CO2 may shift the overall energy budget, causing a modification of skeletal aragonite crystal structures, rather than inhibiting skeletal crystal formation. Consequential to this energy shift, Orbicella faveolata belongs in the category of Scleractinian corals that exhibit a lower sensitivity to ocean acidification.