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Most stony corals liberate their gametes into the water column via broadcast spawning, where fertilization hinges upon the activation of directional sperm motility. Sperm from gonochoric and hermaphroditic corals display distinct morphological and molecular phenotypes, yet it is unknown whether the signalling pathways controlling sperm motility are also distinct between these sexual systems. Here, we addressed this knowledge gap using the gonochoric, broadcast spawning coral Astrangia poculata. We found that cytosolic alkalinization of sperm activates the pH-sensing enzyme soluble adenylyl cyclase (sAC), which is required for motility. Additionally, we demonstrate for the first time in any cnidarian that sAC activity leads to protein kinase A (PKA) activation, and that PKA activity contributes to sperm motility activation. Ultrastructures of A. poculata sperm displayed morphological homology with other gonochoric cnidarians, and sAC exhibited broad structural and functional conservation across this phylum. These results indicate a conserved role for pH-dependent sAC-cAMP-PKA signalling in sperm motility across coral sexual systems, and suggest that the role of this pathway in sperm motility may be ancestral in metazoans. Finally, the dynamics of this pH-sensitive pathway may play a critical role in determining the sensitivity of marine invertebrate reproduction to anthropogenic ocean acidification. [ABSTRACT FROM AUTHOR]

The future of coral reefs under increasing CO2 depends on their capacity to recover from disturbances. To predict the recovery potential of coral communities that are fully acclimatized to elevated CO2, we compared the relative success of coral recruitment and later life stages at two volcanic CO2 seeps and adjacent control sites in Papua New Guinea. Our field experiments showed that the effects of ocean acidification (OA) on coral recruitment rates were up to an order of magnitude greater than the effects on the survival and growth of established corals. Settlement rates, recruit and juvenile densities were best predicted by the presence of crustose coralline algae, as opposed to the direct effects of seawater CO2. Offspring from high CO2 acclimatized parents had similarly impaired settlement rates as offspring from control parents. For most coral taxa, field data showed no evidence of cumulative and compounding detrimental effects of high CO2 on successive life stages, and three taxa showed improved adult performance at high CO2 that compensated for their low recruitment rates. Our data suggest that severely declining capacity for reefs to recover, due to altered settlement substrata and reduced coral recruitment, is likely to become a dominant mechanism of how OA will alter coral reefs. [ABSTRACT FROM AUTHOR]

Coral spawning times have been linked to multiple environmental factors; however, to what extent these factors act as generalized cues across multiple species and large spatial scales is unknown. We used a unique dataset of coral spawning from 34 reefs in the Indian and Pacific Oceans to test if month of spawning and peak spawning month in assemblages of Acropora spp. can be predicted by sea surface temperature (SST), photosynthetically available radiation, wind speed, current speed, rainfall or sunset time. Contrary to the classic view that high mean SST initiates coral spawning, we found rapid increases in SST to be the best predictor in both cases (month of spawning: R2=0.73, peak: R2 = 0.62). Our findings suggest that a rapid increase in SST provides the dominant proximate cue for coral mass spawning over large geographical scales. We hypothesize that coral spawning is ultimately timed to ensure optimal fertilization success. [ABSTRACT FROM AUTHOR]

Most corals in tropical localities broadcast their gametes into the water column, yet we have a poor understanding of what forces reproductive schedules. Moreover, recent studies show considerable geographical variation in the duration of the coral spawning season. For example, on the Great Barrier Reef, corals display tight coupling, while corals in Kenya spawn over seven months. This study reconciles the regional variance by testing the hypothesis that regional wind fields are the corals' ultimate reproductive proxy. Regions with short calm periods should be more tightly coupled than regions with calm periods extending for several months. Regional wind fields were assessed at seven localities, between 1997 and 2006, using the 11 GHz channel radiometer tropical microwave imager (TMI) onboard the tropical rainfall measuring mission (TRMM). There was a direct positive relationship between the duration of regional calm periods and the coupling of mass coral spawning. Ultimate long-term evolutionary advantages of releasing gametes during calm periods ensure fertilization and facilitate larval retention and local recruitment. Coupling mass spawning with seasonally calm periods agrees strongly with recent genetic evidence of local dispersal and high local retention. [ABSTRACT FROM AUTHOR]

Acropora is the most diverse genus of reef-building corals in the world today. It occurs in all three major oceans; it is restricted to latitudes 31°N–31°S, where most coral reefs occur, and reaches greatest diversity in the central Indo-Pacific. As an exemplar genus, the long-term history of Acropora has implications for the evolution and origins of present day biodiversity patterns of reef corals and for predicting their response to future climate change. Diversification of Acropora was thought to have occurred in the central Indo-Pacific within the previous two million years. We examined Eocene fossils from southern England and northern France and found evidence that precursors of up to nine of 20 currently recognized Acropora species groups existed 49–34Myr, at palaeolatitudes far higher than current limits, to 51°N. We propose that pre-existing diversity contributed to later rapid speciation in this important functional group of corals. [ABSTRACT FROM AUTHOR]