Walsh et al,: Juvenile fish assemblages on the southeast United States continental shelf 



257 



cies throughout their life cycle (Browman and Konstan- 

 tinos, 2004). 



Habitat use by juvenile fish has been studied exten- 

 sively along the southeast United States, particularly 

 for commercial and recreational species and structured 

 habitats. For example, there is information available 

 regarding the habitat use of specific estuarine (e.g., 

 Cynoscion nebulosus: Thayer et al., 1999; paralichthid 

 flounders: Walsh et al., 1999) and reef-associated spe- 

 cies (e.g., Mycteroperca microlepis: Ross and Moser, 

 1995; Lutjanus griseus: Chester and Thayer, 1990; 

 Centropristis striata: Lehnert and Allen, 2002). The 

 importance of structural habitat to juvenile fish is also 

 demonstrated by the consistent use of seagrass (Thayer 

 et al., 1999), oyster reef (Meyer and Townsend, 2000), 

 pelagic Sargassum (Moser et al., 1998), mangrove 

 (Thayer et al., 1987), marsh (Hettler. 1989), and rocky 

 reefs (Lindeman et al., 2000). Unconsolidated sedi- 

 ments in estuarine systems and from the surf-zone out 

 into shallow coastal areas (<10 m) are also important 

 juvenile habitat (estuarine: Burke et al., 1991; Walsh et 

 al., 1999; surf-zone: Wenner and Sedberry, 1989; Ross 

 and Lancaster, 2002). 



Despite this large body of research, little is know 

 about the use of unconsolidated sediments on the inner-, 

 mid-, and outer-shelves of the southeast U.S. continen- 

 tal shelf. Unconsolidated sediment is not identified as 

 EFH of the southeast U.S. (SAFMC, 1998), although it 

 is identified in several fishery management plans (red 

 drum, snapper-grouper, rock shrimp, royal red shrimp, 

 coastal migratory pelagics, golden crab, spiny lobsters, 

 and calico scallops). The only offshore habitats that 

 currently have specific protection through their own 

 fishery management plans are coral, coral reefs, live 

 hard bottom, and pelagic Sargassum (Barnette-^; FR, 

 2000). Research in other shelf ecosystems has identi- 

 fied unconsolidated sediments on the shelf as important 

 juvenile habitat (Norcross et al., 1997; Steves et al., 

 2000; Sullivan et al., 2000; Johnson et al., 2001). Fur- 

 ther, unconsolidated sediments on the southeast U.S. 

 continental shelf cover a majority of the area (-60-80%; 

 Parker et al., 1983), and likely serve as juvenile habi- 

 tat for the more than 1200 fish species reported from 

 the ecosystem (estimated from Kendall and Matarese, 

 1994). Thus, well-defined use of unconsolidated sedi- 

 ment habitat by juvenile fish is needed for sediment 

 habitat to be incorporated into future fishery resource 

 management on the southeast U.S. continental shelf. 



Our purpose was to document juvenile fish habitat 

 use and to examine the structure of juvenile fish as- 

 semblages in unconsolidated sediments off the Georgia 

 coast region of the southeast U.S. continental shelf Spe- 

 cific objectives were 1) to provide a list of species that 



•* Barnette, M. C. 2001. A review of the fishing gear utilized 

 within the Southeast Region and their potential impacts on 

 essential fish habitat. NOAA Tech. Memo. NMFS-SEFSC- 

 449, 62 p. (Available from National Technical Information 

 Service, U.S. Department of Commerce, 5285 Port Royal 

 Road, Springfield, VA.] 



use unconsolidated sediments on the shelf as juvenile 

 habitat; 2) to determine which reef-associated species 

 use unconsolidated sediments as juvenile habitat; and 

 3) to describe the relationships between the juvenile as- 

 semblages and environmental factors. The focus on reef 

 fish was motivated largely by the emphasis to protect 

 reef areas by using MPAs, as part of the management of 

 the reef-associated snapper-grouper complex (SAFMC, 

 2001). If species of the reef-associated snapper-grouper 

 complex use unconsolidated sediments during the juve- 

 nile stage, then protection of these habitats should be 

 incorporated into the larger MPA effort. 



Materials and methods 



Study site 



The continental shelf off the Georgia coast is the widest 

 part (200 km) of the southeast shelf. The shelf in this 

 region is gently sloping and comprises four depth zones 

 (Menzel, 1993); inner-shelf (0-20 m); mid-shelf (20- 

 40 m), outer-shelf (40-70 m), and shelf-edge (70-200 m). 

 Each zone has different physical dynamics (Atkinson et 

 al., 1985), climate (Blanton et al., 2003), and larval fish 

 assemblages (Marancik et al., 2005). Demersal habitat 

 consists of unconsolidated sediments, primarily medium 

 to coarse quartz and carbonate sands (Nelson et al., 

 1999) interspersed with rocky reefs (Parker et al., 1983). 

 Reefs of the southeast U.S. shelf range from no relief 

 patchy live-bottom communities, to high-relief ledges. On 

 the shelf off Georgia, rocky-reefs cover about 30% of the 

 bottom (Parker et al., 1983). Rocky-reef habitats have 

 a high diversity of invertebrate (Wenner et al., 1983) 

 and vertebrate faunas (Chester et al., 1984; Parker and 

 Mays, 1998; Lindeman et al., 2000). Located within the 

 continental shelf off Georgia is the 56-km- Gray's Reef 

 National Marine Sanctuary (Gray's Reef NMS, Fig. 1). 

 The sanctuary depth ranges from 18 to 22 m and the 

 benthic macrohabitat is mainly (-75%) unconsolidated 

 sand sediments interspersed with patchy live-bottom 

 and moderate relief (<2 m) hard-bottom ledges (Parker 

 et al., 1994). The adult reef fish community of the sanc- 

 tuary is typical of other inner-shelf (<30 m) reefs of the 

 South and North Carolina shelves (Chester et al., 1984; 

 Parker et al., 1994). 



Collection of juvenile fish and environmental data 



Sampling of juvenile fish was conducted approximately 

 quarterly from April 2000 through February 2002 

 (Table 1). Ten cross-shelf stations (stations 1-7), approxi- 

 mately 18.5 km apart, were sampled during most cruises 

 (Fig. 1). Stations were missed on some cruises owing to 

 weather and equipment failure (Table 1). The cross-shelf 

 transect was 110 km long and stations were sampled 

 on the inner-, mid-, and outer-shelf (10 to 50 m water 

 depth). To avoid sampling within Gray's Reef NMS, four 

 stations were placed immediately adjacent to the four 

 sides of the sanctuary (stations 2.1-2.4). Additional 



