Influence of Florida Current, gyres and wind-driven circulation on transport of larvae and recruitment in the Florida Keys coral reefs

Physical processes with high potential influence on the transport and recruitment of fish, lobster and other larvae in the Florida Keys are discussed using current measurements from standard moored instrumentation, plus bottom mounted Acoustic Doppler Current Profile observations, interdisciplinary surveys of water mass properties, nutrients and planktonic distributions, and satellite derived surface thermal patterns. A cold, cyclonic gyre forms over the Pourtales Terrace seaward of the middle and lower Keys where the Florida Current shifts from eastward to northward flow. Formation of the gyre appears to be related to offshore meander motion of the Florida Current and its cyclonic curvature. Prevailing easterly winds over the gyre circulation cause a convergence of Ekman transports into the coastal zone. The gyre circulation combined with the shoreward convergence of Ekman flow facilitates the transport of pelagic larvae from the Current to the fringing reefs. Duration of the gyre is approximately 1 month, which matches the planktonic stage of fish and slipper lobster larvae, and thus provides a mechanism for larvae retention and local recruitment. Abundant microzooplankton food supply for the larvae is available in the gyre interior due in part to concentration mechanisms and ecosystem response to gyre-induced upwelling of deeper, nutrient enriched waters. Gyre retention times are too short to be a factor in recruitment of locally spawned Florida spiny lobster larvae, which have a planktonic stage that may last up to 12 months. This indicates that Florida spiny lobster should recruit from remote upstream sources in the Caribbean or spend most of their long planktonic stage in Florida Bay of the southwest Florida shelf.