The Reef Environmental Education Foundation (REEF) has been monitoring reef fish assemblages in the Florida Keys National Sanctuary (FKNMS) through its volunteer visual fish census program since 1994. The REEF fish census data set for the FKNMS currently consists of about 5000 surveys collected from 119 sites by more than 400 volunteer divers. This study is an analysis of REEF's fish census data set to determine regional patterns in reef fish assemblage composition within the FKNMS. The correlation between observed regional patterns in fish assemblage composition and habitat heterogeneity (diversity) was also investigated. The Shannon-Weaver Diversity function, pi ln pi, where pi is the proportion of each habitat type at a sampling location, was used as a measure of habitat heterogeneity and was calculated from digitized (Arc View GIS) habitat data obtained from the Benthic Habitat of the Florida Keys CD-ROM Atlas. Methods of analysis along with preliminary results will be discussed.

Shipboard acoustic Doppler current profiler (ADCP) observations of the velocity in the upper 200 m of the water column collected during 1984-1996 using the NOAA Research Vessel MALCOLM BALDRIGE are used to examine the velocity structure and transport in the passages between the Atlantic Ocean and the Intra-Americas Sea (IAS). Data were collected during 23 cruises along the following sections: across the Straits of Florida, in the Northwest Providence Channel (NWPC), across the northern passages into the Caribbean Sea (Windward, Mona and Anegada), across the eastern Caribbean along 63 30'W, thereby forming a closed quadrangle, and in the Grenada Passage. The Florida Current, the eastern Caribbean, and the Grenada Passage share a similar mean velocity structure characterized by high velocity, surface-intensified flows with strong vertical and horizontal shears. The northern Caribbean passages (NWPC, Windward, Mona, and Anegada) share a different common mean velocity structure, with subsurface velocity maxima directed into the IAS, and surface- intensified counterflows along one side of each passage. On average there is a transport balance in the upper 200 m between waters entering and exiting the IAS, with the 16.5 +/- 2.4 Sv (where 1 Sv=10**6 m3/s) transport of the Florida Current at 27N comprised of 0.4 +/- 0.8 Sv from the NWPC, 2.2 +/- 1.5 Sv from the Windward Passage, 2.8 +/- 2.1 and 2.4 +/- 2.8 Sv from the Mona and Anegada Passages, respectively, and 9.5 +/- 4.7 Sv across the eastern Caribbean, for a total of 17.3 Sv. The four passages north of 17N (from NWPC to Anegada Passage) have a combined transport of 7.8 Sv, nearly half of the transport of the Florida Current in the upper 200 m. Of the 9.5 Sv flowing through the eastern Caribbean between 11N and 17N, 4.9 +/- 2.6 Sv, or more than half, come from the Grenada Passage. This is significant to the subject of cross- equatorial exchange of mass, heat and salt, as the Grenada Passage is where the highest transport of waters originating in the southern hemisphere is likely to enter the Caribbean.

The influence of North Brazil Current Rings on the eastern Caribbean is investigated using new results from ship surveys, drifters, TOPEX/POSEIDON altimetry, and a high-resolution North Atlantic model simulation. North Brazil Current Rings are large (~400 km diameter) anticyclonic eddies that periodically pinch off from the North Brazil Current Retroflection and propagate northwestward toward the Lesser Antilles, carrying with them water masses and biogenic materials from the equator and Amazon regions. Results from five years of T/P altimetry and the high-resolution MICOM North Atlantic model now suggest that an average of 5-6 NBC Rings are formed each year, nearly twice what had been previously documented. New shipboard surveys obtained as part of an intensive 1998-2000 in-situ study of NBC rings have shown that these rings can have highly varying vertical structures, ranging from shallow (< 200m) to deep (> 1000m) features, and even subsurface intensified rings with maximum swirl velocities in the thermocline. A similar range of features is produced in the MICOM-simulated rings. As the rings approach the southern Lesser Antilles, they can either break up and disperse their waters through the southern (Windward Island) passages, or move northward as semi-intact features along the outside of the Lesser Antilles to as far as Anegada and the Virgin Islands. Waters from the rings can thus be distributed all along the Lesser Antilles arc and enter the Eastern Caribbean by a number of pathways, a fact which is vividly demonstrated by trajectories from several drifters seeded in NBC rings. The altimetry and model results suggest that the strongest and deepest reaching NBC rings are the ones most likely to travel well northward along the Lesser Antilles arc before breaking up and dispersing their waters. The passage of the rings along the island arc and their interaction with the island topography strongly influences transport variations through the Lesser Antilles passages.