documented enhanced recruitment and 

 vegetative growth of \L echinata in the 

 presence of /L punctulata . 



A north-south gradient in the 

 intensity of fish predation on fouling 

 organisms may be present. Near Beaufort, 

 fish are only occasionally important 

 predators and have little to do with the 

 eventual endpoint of community development 

 (Sutherland 1974). Fish can remove small 

 individuals of the tunicate Styel a 

 pi icata , when they settle on open 

 substrate. However, juveniles of this 

 tunicate commonly find refuges at the base 

 of erect colonies of hydroids and 

 bryozoans, and adults predictably dominate 

 summer assemblages. Near Cape Canaveral, 

 S^ pi icata is predictably removed from 

 shallow water assemblages by sheepshead. 

 This tunicate dominates only when 

 substrates are experimentally isolated 

 from fish predators (Mook 1981). 



4.5 COMPLEX INTERACTIONS 



Experimental marine ecologists have 

 been impressively successful in 

 documenting how competition, predation, 

 and physical disturbances affect community 

 structure (Paine 1966; Dayton 1971, 1975 

 Sutherland 1974; Connell 1975, 1978 

 Lubchenco 1978; Sousa 1979; Ayling 1981 

 Hay 1981b; Hixon and Brostoff 1983 

 Dethier 1984). The best of these studies 

 have also investigated the interactions 

 among the various factors. However, 

 the obvious success achieved by studies 

 focusing primarily on competition, 

 predation, or physical disturbances may 

 have caused ecologists to overlook the 

 importance of more complex, and often 

 indirect, interactions. These 

 interactions can be counter intuitive 

 (i.e. one competitor is dependent on 

 another), and thus are easy to overlook. 

 However, in some cases they may have a 

 major impact on how communities function 

 (Dethier and Duggins 1984; Hay 1986). Two 

 examples of complex interactions that do, 

 or may, occur on jetties in the South 

 Atlantic Bight are described here. 



On jetties in the bight, palatable 

 seaweeds can gain significant protection 

 from herbivorous fishes by associating 

 with abundant competitors that are less 



palatable to these fishes. In fact, when 

 herbivorous fishes are present, palatable 

 seaweeds are completely dependent upon 

 their unpalatable competitors to provide 

 microsites of reduced herbivory that 

 prevent fishes from causing their local 

 extinction. When fishes are excluded, 

 however, the growth rate of palatable 

 species can be severely decreased (by more 

 than 80%) by their association with 

 unpalatable ones (Hay 1986). For these 

 palatable seaweeds, the costs of being 

 associated with an unpalatable competitor 

 are much less than the costs of increased 

 consumption in the absence of that 

 competitor. For the North Carolina jetty 

 community where this interaction was 

 studied, it appeared that removing the 

 dominant (unpalatable) seaweed competitor 

 from the system would cause a decrease, 

 instead of an increase, in the abundance 

 of co-occurring (palatable) competitors 

 (Hay 1986). More recent investigations 

 (Pfister 1987) have shown that these 

 unexpected interactions between competing 

 seaweeds have similar effects on both 

 foraging fishes and sea urchins. 



Although there are no rigorous 

 studies of the recruitment of juvenile 

 fishes to jetties or reefs in the South 

 Atlantic Bight, a New Zealand study (Jones 

 1984a, b) may be instructive for its 

 information on the ecology of a temperate 

 reef fish and for its illustration of 

 complex ecological interactions. Jones' 

 study, as well as extensive work on 

 tropical reefs, suggests that the spatial 

 and temporal changes in distribution and 

 abundance of many species result primarily 

 from patterns of juvenile recruitment 

 (Sale 1980; Williams 1980; Williams and 

 Sale 1981; Doherty 1982, 1983a, b). Jones 

 (1984a, b) showed experimentally that 

 seaweed abundance was critically important 

 in the recruitment of juvenile fish 

 because it provided both cover and food in 

 the form of epifaunal crustaceans. When 

 recruitment was monitored over a wide 

 range of reef habitats, juvenile 

 recruitment at a site was shown to be 

 significantly correlated with algal 

 abundance. Additionally, when seaweeds 

 were removed from some reef areas, 

 recruitment on those areas decreased by 

 87% compared with nearby controls. When 

 algal abundance was experimentally 

 increased by removing herbivorous sea 



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