Unravelling the drivers of coral reproductive phenology and synchrony

Scleractinian corals are the ecosystem engineers of coral reefs, one of the most biodiverse marine ecosystems on the planet. Coral reefs are home to a quarter of all marine species and support the wellbeing and livelihoods of hundreds of millions of people worldwide through fisheries, tourism and coastal protection. Most coral species are broadcast spawners which relay on synchronous spawning events as an essential process for the replenishment and adaptation of populations. Most corals spawn synchronously during short seasonal periods and the timing of these events depends on environmental cues. Given most corals present a short time window in which they release gametes in the water column, fertilization depends on coral colonies adjusting their reproductive timing following the appropriate environmental cues. Moreover, they also depend on releasing gametes with a high degree of synchrony to ensure that outcrossing happen in beneficial environmental conditions. Sea surface temperature, solar insolation, wind speed, lunar phase and cycle have been demonstrated to influence coral spawning and be responsible for month or week of spawning but the mechanisms corals time this event to a particular day still remain unclear. Given the importance of several environmentalcuesin reproductive phenology, climate change impacts could disrupt spawning synchrony, with long-term consequences for population viability.Despite the key role thatcoral reefsplayfor maintaining ecosystem functions and the services they provide to many coastal communities,there is still a need to understand how global-scale human impacts affect coral reproductive timing and synchrony.Until recently, the described impacts of climate change on coral reproductive synchrony have been limitedby a lack of large-scale datasets on coral reproductive phenology, and technical challenges associated with experiments to manipulate seasonal environmental cycles.Previously,the effect of environmental parameters hasbeen studied using broadspatiotemporal scale(e.g., monthly averaged means)and,therefore,identifyingappropriate environmental cues for coral spawning synchrony remains a challenge.

Duringmy Ph.D.I aim to i) determine which climate drivers are more relevant for spawning phenology and synchrony within taxa and ecoregions,ii) investigate which processes and climate drivers are behind different phenological strategies such as split spawning, highlysynchronousvs asynchronousreproductive strategies within assemblages,iii) Evaluate the responses of several taxa to changes in the selected drivers in order to determine which families or species could be more susceptible to experience disruptions in their reproductive phenology and possible breakdowns in spawning synchrony. For this task I will use present, past and predicted future climate scenarios to create ecological models, iv) to identify areas of higher risk to experience asynchronies in coral spawning, creating predictive species distribution models accounting for phenological changes. Such models will help to develop maps of risk of spawning breakdown identifying which species are more vulnerable to different drivers which could help to preserve coral reefs. I am working with a recently compiled, large database on coral spawning timing (CSD), including 6000 individual observations of the time or day of spawning for over 300 coral species, to investigate spatial and temporal patterns of spawning synchrony and phenology. I will use statistical models to test he effect of fine spatiotemporal scale climate drivers on spawning timing. Additionally, I will conduct field and laboratory experiments to test the effects of temperature, lunar cycle and light regime in order to disentangle their effect in coral spawning phenology synchrony.