this jetty. No clear patterns of temporal or spatial similarity were 
observed, and as a result, the cluster dendrogram is not presented here. 
(3). General Discussion 
Numerous studies have assessed the sessile component of 
fouling communities in rocky intertidal and subtidal habitats (see 
Connell, 1972; Paine, 1974 for reviews), but few have examined the highly 
motile epifauna associated with those fouling communities (Dean, 1981). 
This study provided the opportunity to characterize the species composi- 
tion, distribution, and abundance of the motile macroinvertebrates on 
both jetties, and to relate these to the development of the sessile 
community. 
Similarities were observed in the patterns of temporal change in 
abundance, dominance, and species composition between the motile 
epifauna and the sessile biota of the jetties. Both of these biotic 
components achieved high overall densities relatively quickly, particu- 
larly on the south jetty. The dense stands of 7. crocea, which generally 
develop in this geographic area only during periods of low water 
temperature (Woods Hole Oceanographic Institution, 1952) provided 
excellent habitat during the spring of 1980 for several species of motile 
amphipods, including C. penantts. This amphipod is reproductively 
adapted to rapidly colonizing habitats which undergo frequent reduction 
in the density of the sessile inhabitats (Bynum, 1978) such as that 
observed for Tf. crocea. 
Increased faunal richness at the subtidal levels as compared with the 
intertidal zone was also observed within both the motile and sessile 
communities. Dean (1981) noted that the richness of motile species was 
positively correlated with the richness of the sessile species in the 
fouling community he investigated. Similarly, the structurally complex 
community of sessile species, such as ascidians, bryozoans, hydroids, 
and algae found at subtidal levels on the Murrells Inlet jetties, enhanced 
the development of a diverse assemblage of motile species. Dean (1981) 
also described a negative correlation between motile species richness 
and dominance of the sessile fauna by one or a few species. The over- 
whelming dominance by Chthamalus fragilts at upper intertidal levels is 
not conducive to the development of a rich motile epifaunal community at 
those levels on the jetties investigated in this study, where P. 
quadripunetata was the only abundant motile species. 
Certain differences were noted in the development of the sessile and 
motile communities on the jetties. For example, the number of motile 
species on the jetties increased over time, but the number of sessile 
species was relatively constant during the study period. Furthermore, 
the vertical zonation observed among the sessile species was not as well 
defined for the motile forms. The distinct bands of sessile organisms 
are a result of the sedentary nature of these organisms and their compe- 
tition for space in suitable environmental conditions. The motility of 
free-living organisms, on the other hand, allows them to migrate over a 
wide vertical range during periods of submergence. 
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