endpoint of succession appears to be the 

 brown alga, Sarqassum fil ipendula . 



No experimental studies have 

 unambiguously demonstrated the importance 

 of the various physical factors that 

 affect the organization of sunlit, 

 subtidal communities in the South Atlantic 

 Bight. However, the large annual changes 

 in water temperature that occur throughout 

 this region clearly have major direct and 

 indirect effects on benthic community 

 structure. Changes in water temperature 

 appear to be directly responsible for the 

 large-scale migration of most fishes from 

 inshore waters in the winter and for their 

 return in the spring. These migrations 

 probably have a substantial effect on 

 energy transfer from inshore to offshore 

 habitats and on inshore and offshore prey 

 populations. As outlined in previous 

 chapters, temperature changes also have 

 major effects on seaweed and invertebrate 

 populations. Some of these organisms must 

 reinvade rubble structures each year, 

 while others have evolved mechanisms for 

 "over-wintering" as resting stages. 



Wave action also changes seasonally, 

 and winter storms, or large waves 

 generated in other seasons, can have a 

 substantial impact on subtidal 

 communities. Evidence of this can be seen 

 in the large mass of subtidal organisms 

 occasionally deposited on beaches in the 

 South Atlantic Bight. Since much of the 

 bight is devoid of hard substrate in 

 shallow water, waves may have more impact 

 on rubble structures than on natural hard 

 substrate habitats, which are usually 

 deeper. Waves also increase sand scour 

 and turbidity. Both of these factors 

 should significantly affect benthic 

 community structure by killing, slowing 

 growth, or decreasing reproduction of 

 benthic flora and fauna. Sedimentation 

 and scour might be particularly damaging 

 to newly settled juveniles. 



The effects of competition on the 

 organization of sunlit, subtidal 

 communities have rarely been addressed in 

 the South Atlantic Bight. However, 

 experiments have been conducted in hard 

 substrate communities at a depth of 20 m 

 on the Continental Shelf off North 

 Carolina (Peckol and Searles 1983). These 

 experiments indicated that seasonal 



patterns of recruitment and physical 

 disturbance interacted with competitors 

 and consumers to affect the distribution 

 and abundance of both seaweed and benthic 

 invertebrate populations. When settling 

 plates were in cages that excluded large 

 consumers, competition for space occurred. 

 However, community development was 

 dependent upon season of submergence and 

 upon the seasonal growth and recruitment 

 characteristics of the species involved. 

 In this deep and often poorly lit habitat, 

 it appeared that barnacles would have been 

 the competitive dominants had they not 

 been selectively consumed. 



Richardson (1978) conducted a similar 

 study at a depth of 1.5 m below low tide 

 level on the jetty at Radio Island, NC. 

 In his cages, mucous/sand-tube building 

 polychaetes dominated, bivalves and 

 serpulid polychaetes increased, and 

 barnacles and leafy algae decreased in 

 abundance compared to their abundance on 

 plates in open-sided control cages. Some 

 of these changes were interpreted as being 

 a consequence of competition on the caged 

 plates. However, unoccupied space 

 remained at about 50% on plates in the 

 closed cages and it is doubtful that 

 competition caused the reduction in 

 barnacles and leafy algae. Both amphipods 

 and polychaetes along the North Carolina 

 coast have recently been demonstrated to 

 be capable of consuming significant 

 quantities of larger organisms (Hay et al . 

 1987, 1988). A build-up of these organisms 

 in the cages of both of the above 

 mentioned studies could have significantly 

 affected their results (Brawley and Adey 

 1981a, b). Since amphipods and 

 polychaetes are common prey of many fishes 

 (Table 2), their increased abundance in 

 fish exclosures seems likely. 



Both field and microcosm experiments 

 using seaweeds from jetties in North 

 Carolina demonstrate that seaweeds in 

 close association with larger, overstory 

 algae like Sarqassum , experience decreased 

 growth rates due to competition (Hay 1986; 

 Pfister 1987). The consequences of this 

 for community organization have not been 

 adequately evaluated. Given the large 

 role of competition for space, light, and 

 nutrients in other seaweed-dominated 

 communities (Pearse and Hines 1979; Dayton 

 1975; Kastendiek 1982; Reed and Foster 



39 



