Mean distribution and seasonal variability of coastal currents and temperature in the Florida Keys with implications for larval recruitment

Abstract

Long-term moored observations of current and temperature variability have been made along the offshore fringes of the Florida Keys reef tract from Carysfort Reef to the Dry Tortugas as part of multidisciplinary studies of larval recruitment processes (SEFCAR: South East Florida and Caribbean Recruitment) and studies of surface transport processes (SFOSRC: South Florida Oil Spill Research Center). These data are used to make robust estimates of magnitudes and patterns of mean flow and temperature fields in coastal waters of the outer shelf, and are compared to spatial patterns of the mean wind field measured at offshore Coastal Marine Automated Network (CMAN) weather stations and to the change in coastline orientation of the Florida Keys. Five years of moored current meter data from a station seaward of Looe Reef are analyzed using CMAN wind records and Acoustic Doppler Current Profile (ADCP) time series made offshore near the Florida Current front, revealing significant annual cycles in coastal current and temperature fields related to atmospheric and Florida Current forcing. These mean flow patterns and annual cycles are discussed in terms of their impact on larval recruitment pathways. The combined influences of downstream flow of the Florida Current, onshore Ekman transports in the upper layer, coastal countercurrents and cyclonic circulation in the Tortugas gyre tends to aid retention and ultimately recruitment of both locally- and foreign-spawned larvae into the Florida Keys. Seasonal cycles of currents and winds favors enhanced larval recruitment in the fall season of persistent northeast winds that can cause a coastal countercurrent over the entire length of the Keys from Key Largo to the Dry Tortugas, combined with seasonal maximum onshore surface Ekman transports and minimum downstream flow in the Florida Current.