Larval influx of Diadema antillarum to the Florida Keys linked to passage of a Tortugas Eddy

Abstract

Lack of recovery of the sea urchin Diadema antillarum in the Caribbean region following a widespread epizootic in 1983–1984 has garnered great interest due to the role of this species as a grazer of macroalgae that exclude reef-building corals. In the Florida Keys, USA, previous research suggests that reestablishment of D. antillarum is limited by low fertilization success and a lack of larval supply. However, the physical mechanisms determining larval supply in the Florida Keys remain poorly resolved. Here, we use coupled biological and physical oceanographic datasets of D. antillarum larval supply to settlement collectors, sea surface temperatures and heights, and the Okubo Weiss parameter to examine a link between influx of larvae to the middle Florida Keys and Tortugas Eddy activity in the Straits of Florida. The greatest magnitude of settlement over 3 months of measurements occurred from late May to late June 2015, coinciding with the passage and dissociation of a Tortugas Eddy. Settlement occurred on collectors only at offshore bank-barrier reef sites, consistent with a temperature signal of a passing eddy at these sites. No D. antillarum were observed by divers at sites 1 yr following settlement on the collectors. The results indicate that despite the lack of population recovery, D. antillarum larval influx can occur during intermittent oceanographic events.