being resistant to seaweed chemical 

 defenses that deter co-occurring fishes. 

 However, there are still no data to 

 suggest that these small grazers sequester 

 the algal metabolites and thereby directly 

 reduce their acceptability as prey to 

 local fishes (Hay et al . 1987). The 

 effects of small grazers on algal 

 community structure clearly warrants 

 increased attention. 



Given the large impact that 

 herbivorous invertebrates have been shown 

 to have on temperate algal communities, it 

 is surprising that more attention has not 

 been focused on the effects of temperate 

 herbivorous fishes. These fishes are 

 abundant in the South Atlantic Bight 

 (Figure 26), are very mobile, search 

 visually, and have high metabolic rates 

 relative to co-occurring invertebrate 

 herbivores. It would be surprising 

 therefore if they did not have a large 

 impact on the organization of subtidal 

 community structure. Choat (1982) 

 recently reviewed feeding by fishes in 

 temperate waters and its effects on 

 benthic community structure. He compiled 

 an impressive list of studies that suggest 

 that temperate herbivorous fishes have the 

 potential to affect benthic community 

 structure. However, he concluded that no 

 studies had clearly demonstrated extensive 

 modification of temperate, hard-substrate 

 biota by grazing fishes. 



The following families of herbivorous 

 fishes occur in the South Atlantic Bight: 

 Sparidae, Bleniidae, Kyphosidae, Mono- 

 canthidae, Mugilidae, and Pomacentridae. 

 Of these, the Sparidae (pinfish, spottail 

 pinfish, and sheepshead) probably have the 

 greatest impact on the community organ- 

 ization of rubble structures because they 

 are often the most abundant fishes in 

 shallow waters (Adams 1976b; Darcy 1985a, 

 b; Hay 1986). They also consume large 

 quantities of benthic macrophytes (Carr and 

 Adams 1973; Adams 1976a; Ogburn 1984; Darcy 

 1985a, b; Lindquist et al . 1985). As an 

 example, Table 4 shows the stomach contents 

 of 21 spottail pinfish collected from the 

 jetty at Radio Island, NC during late 

 summer. Approximately 98% of the dry mass 

 of stomach contents was plant material. 

 Carr and Adams (1973) reported similar data 

 for several size classes of spottail 

 pinfish ranging from 26 to 167 mm; 50% to 



90% of the volume of their stomach contents 

 was algae. When offered a variety of 

 common macrophytes in the lab, both pinfish 

 and spottail pinfish showed a strong 

 preference for some species and consumed 

 very little of others (Hay et al . 1987, 

 1988; and Figure 27). During mid- to late- 

 summer, high preference species such as 

 Hypnea and Calonitophyllum show dramatic 

 declines in abundance as fish numbers and 

 sizes increase. Low preference species such 

 as Sarqassum , Padina , and Dictyota increase 

 or show no change in abundance at this time 

 (M. Hay; pers. obser.). 



To assess the potential effects of 

 temperate herbivorous fishes on the 

 organization of subtidal jetty 

 communities, Hay (1986 and work in 

 progress) constructed eight 5,000-L 

 outdoor microcosms that were designed to 

 mimic the nearby jetty at Radio Island, 

 NC. Each microcosm was divided by 1.5 cm 

 plastic mesh into two equal sized parts of 

 1 nr each. The mean wet mass/m of all 

 common algae from the jetty was attached 

 to the bottom and sides of each partition, 

 and the mean field density of each common 

 herbivorous or omnivorous fish was placed 

 in one portion of each microcosm. 

 Spottail pinfish were stocked at a density 

 of 8/m 2 ; pinfish and planehead filefish, 

 Monpcanthus hi spidus , were stocked at 

 1/m. Five new cinder blocks were added 

 to each side of each microcosm and were 

 monitored at 2- to 4-week intervals for 

 presence and percent cover of all animal 

 and plant species. The same cinder blocks 

 were monitored without replacement for the 

 entire 4 month study . All microcosms 

 were located immediately adjacent to Bogue 

 Sound and received continuous inputs of 

 unfiltered sound water through an 

 apparatus which also generated waves. The 

 water in the microcosms turned over every 

 45-90 minutes. 



Between the initiation of the 

 experiment in early August and termination 

 in late November, fishes: (1) 

 significantly reduced the abundance and 

 rate of establishment of 111 va , 

 Enteromorpha , small filamentous algae, and 

 all of the common red seaweeds ( Hypnea , 

 Spyridia , Chondria , Champia , Pol ysiphonia , 

 Graci 1 ari a , and Neoaqardhi el 1 a ) , (2) 

 significantly increased the abundance of 



42 



