Marancik et al .: Fish assemblages on the southeast United States continental shelf 



109 



of larval fish assemblages in this area. For example, 

 during the RV Dolphin cruises, the Marine Resources 

 Monitoring, Assessment, and Prediction (MARMAP) 

 cruises, and the Southeast Area Monitoring and As- 

 sessment Program (SEAMAP) cruises, ichthyoplankton 

 surveys were conducted on the southeast United States 

 continental shelf. From these surveys, spawning time 

 was denned for a large group of species (Fahay, 1975), 

 and the temporal and spatial distribution of larvae 

 were described for a few select species (Kendall and 

 Walford, 1979; Collins and Stender, 1987; 1989; Smith 

 et al., 1994) and for multiple taxa, but mostly at the 

 family level (Powles and Stender, 1976). Similarly, other 

 programs (e.g., the South Atlantic Bight Recruitment 

 Experiment) examined spawning and larval transport 

 of "estuarine-dependent" species such as Atlantic men- 

 haden (e.g., Judy and Lewis, 1983; Hoss et al., 1997; 

 Hare et al., 1999; Checkley et al., 1999), but results for 

 the entire suite of species sampled were not reported. 

 For studies where the broader community of larval fish 

 on the southeast U.S. shelf was addressed, the structure 

 and dynamics of larval assemblages were not defined 

 (Powell and Robbins, 1994, 1998; Govoni and Spach, 

 1999; Powell et al., 2000). 



The purpose of this study was to examine larval fish 

 assemblages on the continental shelf off the coast of 

 Georgia, USA. This region of the continental shelf was 

 targeted because of 1) the nature of the broad shallow 

 shelf, 2) the location of Gray's Reef National Marine 

 Sanctuary 20 km from shore, and 3) the location of sev- 

 eral proposed deepwater MPAs (70-200 m water depth) 

 in the region. Temporal and spatial patterns in larval 

 distributions were described to explain spawning and 

 larval transport processes on the continental shelf off 

 the coast of Georgia, and the implications for MPAs in 

 the region were addressed. 



Materials and methods 



Study site 



The southeast United States continental shelf extends 

 from West Palm Beach, Florida, to Cape Hatteras, North 

 Carolina. Moving north from West Palm Beach (15 km), 

 the shelf widens to Georgia (200 km) and then narrows 

 to Cape Hatteras (35 km). Physical forcing by the Gulf 

 Stream, which is part of the North Atlantic Western 

 Boundary Current system, varies along the shelf. As 

 the Gulf Stream flows northward along the shelf edge, it 

 meanders, and cyclonic frontal eddies form in meander 

 troughs (Lee et al., 1991). Meanders and frontal eddies 

 grow in dimension from just north of the Straits of Florida 

 (27°N latitude) to St. Augustine, Florida (30°N latitude), 

 and then decrease from St. Augustine to just south of 

 Charleston, South Carolina (32°N latitude). Meanders and 

 frontal eddies grow in dimension again downstream of the 

 Charleston Bump (32-33°N latitude), and then decrease 

 again from Cape Fear, North Carolina (33°N latitude), to 

 Cape Hatteras, North Carolina (36°N latitude). 



In addition to along-shelf variation in geophysical 

 structure and Gulf Stream forcing, the southeast Unit- 

 ed States continental shelf can be divided into three 

 cross-shelf zones based on physical circulation dynamics 

 (Boicourt et al., 1998). Circulation on the inner-shelf 

 (0-20 m water depth) is influenced by tidal currents, 

 river inflow, and wind (Atkinson and Menzel, 1985; Pi- 

 etrafesa et al., 1985a). Wind-driven flow predominates 

 on the mid-shelf (20-40 m water depth) and there is 

 only minor Gulf Stream and tidal influence (Atkin- 

 son and Menzel, 1985). Flow on the outer-shelf (40-75 

 m water depth) is dominated by the passage of Gulf 

 Stream frontal eddies and upwelling at the shelf break 

 (Pietrafesa et al„ 1985b). 



Inner and mid-shelf physical processes are relatively 

 more important off the coast of Georgia compared to 

 other segments of the southeast United States conti- 

 nental shelf (Boicourt et al., 1998). The continental 

 shelf off the coast of Georgia is the area of diminish- 

 ing meanders and eddies from St. Augustine, Florida, 

 to Charleston, South Carolina. Tidal range and fresh- 

 water inflow is greatest in the Georgia portion of the 

 southeast shelf (Atkinson and Menzel, 1985). Further, 

 because the shelf is widest off the coast of Georgia (ap- 

 proximately 200 km), the Gulf Stream is less influential 

 on mid- and inner-shelf dynamics compared to the rest 

 of the southeast United States continental shelf (Lee 

 et al., 1991). 



Collection of larval fish and CTD data 



Ichthyoplankton sampling was conducted approximately 

 every other month from April 2000 through February 

 2002 (Table 1). A maximum of ten stations, approxi- 

 mately 18.5 km apart, were sampled during each cruise. 

 Stations were missed on some cruises owing to weather 

 and equipment failure. The transect was 110 km long 

 and spanned 10 to 50 m water depth (Fig. 1). Four sta- 



