WENNER AND WENNER: CRUSTACEANS FROM COASTAL HABITATS 



Wenner and Read (1982) found that Trachypenaeus 

 constrictus, Portunus spinimayius, P. gibbesii, and 

 Ovalipes stephensoni form a frequently co-occurring 

 assemblage on the inner shelf. Although their impor- 

 tance in terms of abundance and biomass changed 

 seasonally, all species in groups A and B, except 

 Caliinectes omafiis, were collected during every 

 sampling period, indicating that these species are 

 a core-assemblage of the coastal zone. Several spe- 

 cies in these groups (0. ocellatus, P. gibbesii, and 

 P. spinimanus) are common inhabitants of high- 

 salinity estuarine waters in South Carolina (Wen- 

 ner et al. 1984) and Georgia (Hoese 1973), while 

 others, such as C. sapidus, Penaeus setiferus, and 

 P. aztecus, are migratory and seasonally dominant 

 inhabitants of estuarine systems in the southeastern 

 United States (Weinstein 1979; Wenner et al. 1983, 

 1984). Another member of this assemblage, Are- 

 naeus crihrarius, is a common member of the sandy 

 beach community along the southeastern United 

 States (Pearse et al. 1942; Williams 1984; Ander- 

 son et al. 1977; Leber 1982; DeLancey 1984). 



Species from groups C and D were restricted to 

 sites as indicated by moderate to high fidelity values 

 and have previously been reported as nearshore in- 

 habitants of the southwestern Atlantic (Williams 

 1984). Most species in these groups are found on 

 sand or mud bottom and occur throughout the lati- 

 tudinal extent of the study area (Williams 1984). Ex- 

 ceptions include Portunus sayi which is commonly 

 associated with Sargassum (Williams 1984), and 

 Hepatus pudibundus which has not been reported 

 north of Georgia (Coelho and Ramos 1972). Species 

 in Group E are generally associated with hard- 

 bottom areas (Wenner and Read 1982; Williams 

 1984) and were neither abundant or commonly en- 

 countered in the coastal habitat. These species were 

 most restricted in their distribution to collections 

 from site group 7. 



Group E contained species which were not con- 

 stant or faithful to any site groups. In addition, there 

 was no consistency in their occurrence with regard 

 to season, latitude, or substrate preference. Most 

 of the species in this group have broad bathymetric 

 ranges on the continental shelf and none were abun- 

 dant in our collections from the coastal zone. 



Seasonality and latitude are important factors 

 determining species assemblages in coastal habitats. 



Figure 2.— Normal cluster dendrogram of site groups formed 

 using percent standardization and flexible sorting. Data from stan- 

 dard tows during a season were pooled within each stratum. 



The grouping of strata by season suggests that the 

 decapod and stomatopod fauna of the coastal zone 

 changes throughout the year and may also change 

 with latitude. Although changes in species composi- 

 tion occur seasonally, most species groups deline- 

 ated by cluster analysis were not consistently col- 

 lected nor restricted to particular site groups. A 

 seasonally ubiquitous faunal assemblage in the 

 coastal zone was composed of numerically dominant 

 species. The species assemblages which were char- 

 acterized as being restricted to site groups consisted 

 of relatively rare species or those which were asso- 

 ciated with hard-bottom habitat. 



Temporal and Spatial Distributions 

 of Numerically Dominant Species 



Portunus gibbesii 



Although its known range extends from southern 

 Massachusetts through the Gulf of Mexico, this por- 

 tunid crab is more common and abundant in shallow 

 shelf waters of the Carolinean Province and Carib- 

 bean Sea (Williams 1984). Portunus gibbesii has 

 been reported on mud, sand, and shell substrates 

 (Park 1969, 1978). 



This species far outranked other decapod and 

 stomatopod crustaceans in total number (24% of the 

 total catch) and was present in 273 of the 303 col- 

 lections made during all seasons (Table 1). In terms 

 of biomass, P. gibbesii was the fifth most important 

 species collected, constituting 9% of the total catch 

 by weight. Abundance differed seasonally, with the 

 stratified mean catch per tow being highest in fall 

 (79 individuals/tow) and lowest in winter (26 indivi- 

 duals/tow) (Table 5). The number of individuals per 

 tow differed between areas with more P. gibbesii 

 collected in strata off Georgia during every season 

 (Fig. 4). 



The mean size of P. gibbesii differed between 

 areas with largest crabs (x CW = 50 mm, n = 

 1,484) caught off Florida. Crabs off Georgia aver- 

 aged 44 mm CW (n = 2,347), while those from strata 

 off South Carolina/North Carolina averaged 41 mm 

 CW (n = 3,158), suggesting decreased size with in- 

 creasing latitude. Mean size of P. gibbesii differed 

 between seasons, with smallest individuals collected 

 in summer (x CW = 37.5 mm, n = 1,985). Mean 

 carapace width of individuals was similar during 

 other seasons (winter: x = 46.9 mm, n = 609; 

 spring; (x = 48.2 mm, n = 1,305; fall; x = 45.9 

 mm, n = 3,090). Seasonal size differences may 

 reflect influx of crabs from a spring hatch. Ovig- 

 erious females occur off Beaufort Inlet, NC from 



163 



