Distribution and Diversity of Sediment-Dwelling Echinoids of the Central Florida Keys

Sediment-dwelling echinoids, such as clypeasteroids (sand dollars and sea biscuits) and spatangoids (heart urchins), are important ecosystem engineers found in many soft-bottom habitats around the Florida Keys. Several studies, conducted over the last five decades, have documented their spatial distribution and diversity in various areas of the Florida Keys. This study focuses on the central part of the Florida Keys, an area that has been subject to diverse human impacts including tourism, fishing, boating, and diving leading to pollution, eutrophication, and intrusion of non-native species. All these stressors can potentially undermine the ecosystem’s composition and health, including sediment-dwelling echinoids. To assess the current state of echinoid populations, 27 sites located along the central part of the Florida Keys have been surveyed by SCUBA (2020-2021) for presence of live specimens and dead skeletal remains of clypeasteroid and spatangoid echinoids. A total of 17 out of 27 sites were inhabited by sediment-dwelling echinoids of the species Clypeaster rosaceus, Clypeaster subdepressus, Encope michelini, Leodia sexiesperforata, Meoma ventricosa, and Plagiobrissus grandis. Up to five species co-occurred at single sites, although most sites harbored only one or two species, and at all sites a single species was dominant in terms of relative abundance. The most widespread and abundant species in the surveyed area were Clypeaster rosaceus, Leodia sexiesperforata, and Meoma ventricosa. A comparison of live specimens with skeletal echinoid remains indicates that dead tests are typically much rarer than live specimens. However, the spatial distribution and abundance of dead remains tracks live occurrences: when dead remains are found, live specimens are always observed. The comparison of the new survey reported here with past studies and database records suggests that the faunal composition of sediment-dwelling echinoid assemblages has not changed notably over the past 50 years.