Millennial-scale dynamics of sea urchin communities on Tropical Eastern Pacific reefs

Speed talk
11:00, vendredi 20 déc. 2019 (5 minutes)
Salle ABCD
Sea urchins play an important grazing role on coral reefs and their abundances shift in complex ways with respect to both top-down and bottom-up processes. Reef cores have previously been used to reveal the dynamics of urchin abundances over millennia, but never in the Tropical Eastern Pacific (TEP). In this study, we reconstructed the dynamics of urchin communities over millennia in relation to habitat type on two reefs in the Las Perlas Archipelago, Pacific Panama. From four reef-cores we recovered 126 samples spanning back over 5000 years to reconstruct patterns of sea urchin and coral abundance through time. We picked and identified all urchin spines >500 µm to the level of species. We used the weight of urchin spines and coral fossils to determine the changes in relative abundance of each taxon and document species richness and diversity over time. Seven urchin taxa were found across all samples, with Eucidaris and Diadema consistently dominant. Our results show a general pattern of increasing urchin abundances towards the present on both reefs. We observed that total sea urchin abundance was positively correlated with coral abundance and negatively correlated with abundance of calcareous algae confirming previous findings of urchin preferences. However, the abundance of the dominant urchin, Eucidaris and Diadema, was correlated with neither coral nor calcareous algae, suggesting some level of functional redundancy in habitat use. These records can complement neontological studies, explore ecological mechanisms and help place our understanding of modern reef dynamics into larger temporal contexts.

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