1984; Santelices and Ojeda 1984), the 

 importance of competition in structuring 

 sunlit, benthic communities in the South 

 Atlantic Bight deserves more attention. 



Competition among fishes in the South 

 Atlantic Bight has not been studied, but 

 given the high degree of diet overlap 

 among many fishes on jetties (Table 2) and 

 the high densities of these fishes, 

 competition seems likely. If intra- 

 specific competition for food occurs, then 

 the growth of immature fishes should be 

 density dependent. This pattern has been 

 documented on several occasions and is 

 widespread in marine fishes (Anthony 1971; 

 Cushing and Horwood 1977; Leggett 1977; 

 Rauck and Zijlstra 1978; Jones 1984a, b) . 

 However, the importance of interspecific 

 competition in juvenile stages of temperate 

 reef fishes has not been investigated. 



distribution and the organization of 

 benthic communities in general, have been 

 remarkably fruitful. They have provided 

 both ideas and a data base for many of the 

 generalizations in the current ecological 

 literature (Dayton 1971, 1975; Menge and 

 Sutherland 1976; Lubchenco 1978; Sousa 

 1979; Paine 1980; Lubchenco and Gaines 

 1981; Gaines and Lubchenco 1982). The 

 effects of grazing invertebrates on the 

 organization of sunlit, subtidal 

 communities in the South Atlantic Bight, 

 however, are largely uninvestigated. Both 

 Richardson (1978) and Peckol and Searles 

 (1983) demonstrated that exclusion of 

 large consumers could significantly affect 

 benthic prey populations. However, their 

 experiments did not separate the effects 

 of the invertebrates (urchins, large 

 crabs, etc.) from those of the fishes, so 

 the effects of invertebrates alone are 

 unknown. 



For the many juveniles that use 

 rubble structures and estuaries as 

 nurseries, competition from abundant 

 omnivorous fishes, like pinfish and 

 spottail pinfish, could be particularly 

 acute. In shallow habitats along portions 

 of the bight, pinfish and spottail pinfish 

 may comprise more than 50% of the total 

 fish standing stock during the summer and 

 fall. This is also the time when feeding 

 by fishes has reduced the abundance of 

 epifaunal prey to yearly lows (Thayer et 

 al . 1975; Adams 1976a; Nelson 1979, 1980a, 

 b; Darcy 1985a, b). Because the diets of 

 these sparid fishes overlap substantially 

 with the diets of juvenile gag, spot, 

 black sea bass, and others (Adams 1976a; 

 Link 1980), competition between these 

 species and sparids could be particularly 

 important. 



One advantage that sparids may have 

 is the ability to feed on plant material 

 when crustacean populations have been 

 depleted. This may allow them to maintain 

 high densities that prevent the recovery 

 of crustaceans and therefore make the area 

 of marginal value for other juvenile 

 fishes. Jones (1984a, b) provides several 

 lines of evidence suggesting that juvenile 

 temperate fishes might be limited by the 

 abundance of epifaunal prey. 



Temperate investigations of how 

 herbivorous invertebrates affect algal 



The most obvious invertebrate 

 herbivores on jetties in the bight are sea 

 urchins. No field experiments have been 

 conducted to assess their effects on 

 community structure. Hay et al . (1986) 

 present some data on the jetty seaweeds 

 that are preferred and avoided by the 

 common sea urchin Arbacia punctulata , and 

 on its chemoattraction toward these 

 seaweeds. Some low preference seaweeds 

 like the brown alga Dictyota dichotoma 

 are chemically defended against Arbacia 

 (Hay et al . 1987). Pfister (1987) has 

 also demonstrated that palatable seaweeds 

 gain some protection from grazing Arbacia 

 by being closely associated with 

 unpalatable seaweeds like the brown alga 

 Sargassum fil ipendula . The consequences 

 of these types of interactions are 

 discussed at greater length in the section 

 on complex interactions. Given the 

 significant effects that sea urchins have 

 been shown to have in other benthic marine 

 communities (Lawrence and Sammarco 1982), 

 it is probable that sea urchins, when 

 abundant, significantly affect the 

 organization of communities on rubble 

 structures in the bight. 



Other common herbivorous inverte- 

 brates include amphipods, isopods, crabs, 

 gastropods, and polychaetes. These can be 

 important herbivores in some habitats 

 (Steneck and Watling 1982; Hawkins and 

 Hartnoll 1983) but little is known of 



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