Abstract:
Corals are foundational species on coral reefs, but despite their importance, coral populations are declining worldwide as a result of anthropogenic and natural disturbances. This unprecedented decline has emphasized the need to focus on the processes able to promote recovery of diverse coral communities after a disturbance such as larval recruitment. Recruitment of new individuals is mediated by a variety of physical, biological, and chemical cues. Crustose coralline algae (CCA) and their bacterial biofilms have been identified as positive settlement cues for some species of scleractinian corals, but the exact conditions necessary for corals to settle remain highly debated. In an attempt to determine the origin of the compound(s) responsible for the settlement of Porites astreoides and Diploria labyrinthiformis larvae, a series of experiments utilizing chemical and physical modifications of two species of CCA were performed. Various extraction techniques were used to recover the natural products produced by the CCA and multiple concentrations of these compounds were tested on D. labyrinthiformis larvae. Results confirmed the important role of CCA in the settlement of scleractinian corals and identified species specific differences among corals and algae tested. Methanol:ethyl acetate extractions yielded the most active compounds and extraction efficiency was greatly improved when CCA were freeze dried prior to extraction. If larvae were exposed to crude extracts at concentrations too high, no settlement was observed. Optimal settlement occurred at a concentration of 2.5 µg/ml, and future studies will investigate if this concentration is ecologically relevant. These results suggest that efforts to protect and restore coral reefs need to advocate for a variety of taxa, as diverse reefs are more likely to support diverse coral communities.

Bio:
Aurora Giorgi is currently a postdoctoral researcher in the Global Change Ecology lab in the Red Sea Research Center working on crustose coralline algae taxonomy and larval settlement. In 2022 she finished her PhD at the University of Alabama where she studied the diversity of crustose coralline algae (CCA) in the western tropical Atlantic region in order to examine their role in coral larval settlement. During her PhD she was awarded the Link Fellowship at the Smithsonian Marine Station in Fort Pierce, thanks to which she was able to investigate whether larval settlement is mediated by intrinsic factors (compound produced by CCA), extrinsic factors (compound produced by the surface microbial community of the CCA), or by an interaction of both