FISHERY BULLETIN: VOL. 87, NO. 1 



not appear to be habitat-restricted, nor did they ex- 

 hibit a meaningful distribution pattern (Clifford and 

 Stephenson 1975), as indicated by the tendency of 

 the entities to chain rather than form new groups. 



Species and pooled collections from a stratum 

 were classified using flexible sorting (Lance and 

 Williams 1967) with a cluster intensity coefficient 

 (^) of -0.25. The similarity coefficient used was the 

 Bray-Curtis measure (Clifford and Stephenson 1975) 

 on percent standardized data (Boesch 1977). 



The postclustering technique of nodal analysis 

 (Williams and Lambert 1961; Lambert and Williams 

 1962) was used to describe site groups in terms of 

 their characteristic species and species groups in 

 terms of their occurrence within site groups. Nodal 

 analysis interpretations were made by using pat- 

 terns of constancy (a measure of how consistently 

 a species is found in a site group) and fidelity (a 

 measure of how restricted a species group is to a 

 site group). Mathematical definitions of constancy 

 and fidelity and a more detailed explanation of 

 cluster and nodal analysis are found in Boesch 

 (1977). 



RESULTS AND DISCUSSION 



Hydrographic Measurements and 

 Description of the Study Area 



The coastal zone as defined by Struhsaker (1969) 

 ranges from the beaches to 16-24 km offshore 

 where the water depth is 9-18 m. The sea bottom 

 within this depth zone is mostly homogeneous in 

 composition, consisting predominantly of sandy mud 

 with varying amounts of ground-shell. The bottom 

 is ripple-marked by wave action to a depth of 20 m 

 (Sandifer et al. 1980). Hard or "live" bottom reefs 

 are interspersed throughout the coastal zone (Bu- 

 chanan 1973) and are distinguished from the sur- 

 rounding sand biotope by supporting a diverse 

 assemblage of sessile invertebrates as well as 

 numerous motile species which are inhabitants of 

 the complex microhabitats (e.g., rock crevices, bare 

 rock, ledges with sand veneer, sand patches between 

 rocks, and sessile organisms) of the reefs (Wenner 

 et al. 1983). 



The hydrography of the coastal zone has not 

 been studied as thoroughly as other areas of the con- 

 tinental shelf. The interacting forces of river runoff, 

 wind direction and force, seasonal air temperatures, 

 and proximity of the Gulf Stream produce com- 

 plicated patterns of circulation (Rumpus 1973) 

 that determine the distribution of sediments, 

 nutrients, oxygen, temperature, salinity, food, and 



planktonic forms of larval and adult organisms 

 (Johnson et al. 1974). Bumpus (1973) observed that 

 the southerly flowing coastal current is very tran- 

 sient and restricted to a narrow band along the 

 coast. 



Nearshore surface and bottom waters off the 

 southeastern United States have large seasonal vari- 

 ations in temperature. Because of the shallowness 

 of the coastal zone, cooling and warming can occur 

 rapidly when appropriate atmospheric conditions 

 exist; when the amount of cold, fresh, runoff is vari- 

 able; or when the movement of the Gulf Stream is 

 variable (Mathews and Pashuk 1984). A well-defined 

 recurrent seasonal upwelling exists off the coast of 

 Florida near Cape Canaveral, which occurs in late 

 July with anomalously low multiyear monthly mean 

 surface temperatures (Smith 1983; Lee and Pietra- 

 fesa 1987). Warming of bottom waters usually oc- 

 curs in late August. 



Mean bottom water temperatures for each 

 stratum during the present study increased with 

 decreasing latitude for every sampling period ex- 

 cept summer (Fig. 1). During that time, tempera- 

 tures ranging from 20.0° to 23.1°C were noted off 

 the coast of Florida, while the extremes recorded 

 for strata off North Carolina, South Carolina, and 

 Georgia were 25.5°-29.7°C. Temperature extremes 

 during the other sampling periods varied predictably 

 with latitude. During winter sampling, temperatures 

 ranged from a low of 7.2°C off North Carolina to 

 15.1°C at the southernmost stratum off Florida. 

 Temperatures in spring were the least variakyie with 

 regional extremes of 20.2°-23.9°C noted. The 

 lowest temperatures were recorded in strata be- 

 tween Charleston, SC and Savannah, GA. Tem- 

 peratures during the fall sampling ranged from 

 16.6° to 23.9°C, with the lowest temperatures again 

 occurring for strata between Charleston and 

 Savannah. 



Salinity of nearshore waters is generally lower 

 than that of the open shelf because of runoff from 

 rivers. Blanton and Atkinson (1978) noted that 

 runoff into the coastal zone is bimodal with a major 

 peak in spring and a minor peak in late summer. 

 Because most of the freshwater on the open shelf 

 is confined to depths <20 m, salinity regimes 10 or 

 20 km off the Georgia coast are similar to those of 

 a partially mixed estuary. Rapid mixing occurs due 

 to large tidal fluxes (Blanton and Atkinson 1978). 

 Salinities of bottom waters measured during the 

 present study were fairly uniform seasonally. High- 

 est values were noted for coastal waters off the coast 

 of Florida, while lowest salinities occurred off South 

 Carolina and Georgia (Fig. 1). 



158 



