FISHERY BULLETIN: VOL. 85, NO. 2 



serious impacts on many commercially important 

 fisheries. Our own data imply a potentially negative 

 impact on hard clam recruitment (Table 4) and a 

 clear reduction in bay scallop abundance (Table 8) 

 in part because of reduction in seagrass biomass. 



Clam harvesting had no detectable effect on the 

 abundance of small benthic invertebrates. The den- 

 sity data did not even suggest an effect (Table 6) 

 and the composition of the most abundant species 

 did not change, even with intense clam kicking 

 (Table 7). This lack of response is probably a conse- 

 quence of the dominance of small polychaetes in 

 these invertebrate data. Small polychaetes make up 

 most of the total infaunal density and all of the most 

 abundant species. Small polychaetes tend to exhibit 

 rapid turnover, quick colonization and short life 

 spans, relative to molluscs, echinoderms, and many 

 other invertebrates; consequently, they may be ex- 

 pected to recover more rapidly after disturbance. 

 The large seasonal variability in total macroinver- 

 tebrate density at our seagrass sites is a reflection 

 of the short-term response times of this fauna, which 

 is known to exhibit large seasonal fluctuations in 

 density in North Carolina (Commito 1974). 



Like several previous studies of the densities of 

 benthic infauna (Kikuchi 1966; Warme 1971; Orth 

 1977; Reise 1977, 1978; Stoner 1980; Summerson 

 and Peterson 1984), our data demonstrate higher 

 densities inside the seagrass bed than on unvege- 

 tated bottoms in October. However, the difference 

 in infaunal density between habitats appears to vary 

 seasonally, as shown previously (Reise 1978; Stoner 

 1980). In spring, the two habitats had approximately 

 equal densities of infauna. Because estuarine den- 

 sities of epibenthic predators, both fishes (Adams 

 1976; Orth and Heck 1980) and crustaceans (Heck 

 and Orth 1980), also vary seasonally such that our 

 fall samplings occur after months of high density 

 and our spring samplings after a low-density season 

 for epibenthic consumers, these new observations 

 provide further support for the hypothesis (see 

 review of concepts in Kikuchi 1980; experimental 

 evidence in Reise 1977; Orth 1977; Summerson and 

 Peterson 1984) that seagrass provides a natural 

 refuge from predation for infaunal invertebrates. 



Intense clam kicking caused a substantial decline 

 in the average density of bay scallops in the seagrass 

 habitat (Table 8). Most of the variation among 

 matrices in the total densities of bay scallops and 

 in the fall 1983 densities, when numbers were high, 

 could be readily explained by the variation among 

 matrices in average seagrass biomass. Bay scallops 

 recruit to seagrass blades where they remain at- 

 tached by byssal threads for the first few months 



of life. In addition, adult bay scallops, which are 

 mobile, tend to be found in seagrass beds, as our 

 failure to encounter them in the sand-flat samples 

 illustrates. Their feeding may be more efficient in 

 the slower currents of the seagrass environment 

 (Kirby-Smith 1972). Consequently, it is not surpris- 

 ing that reductions in bay scallop density accom- 

 panied the declines in average seagrass biomass in 

 our experiments. However, the apparent effect (Fig. 

 5) of intense clam kicking that persists even after 

 the seagrass biomass effect is removed was a sur- 

 prise. Because the application of clam kicking is 

 necessarily patchy (it forms a trail behind the path 

 of the boat) and, thus, produces an increase in the 

 patchiness of the vegetation (see standard errors in 

 Table 5), we suspect that this residual effect of in- 

 tense clam kicking is a reflection of that enhanced 

 seagrass patchiness. We hypothesize that the aver- 

 age biomass of seagrass present in our plots is more 

 attractive (in a broad sense) to bay scallops when 

 it is more uniformly distributed over a given area 

 than when it is clumped into more discrete patches 

 at least on the 0.25 m- scale of our samples. 



The implications of this study for the management 

 of the hard clam fishery depend upon the specific 

 values attributed to various factors. Our data show 

 clearly the enhanced efficiency that the mechanical 

 clam harvesting process known as clam kicking 

 brings to the fisherman who adopts it instead of 

 hand raking. Yet the enhanced efficiency may itself 

 be a danger if the resource is thereby overfished 

 beyond its capacity to sustain harvest. Our data on 

 the negative impacts of clam harvest do not permit 

 one method to be selected in preference to another 

 except to the degree that hand raking might never 

 reach the same harvest intensity and, therefore, 

 might not cause the same magnitude of effects on 

 seagrass beds and their fauna. Outside seagrass 

 beds, clam kicking does not appear to have any 

 serious negative impacts on other parameters of 

 ecological value with the possible exception of hard 

 clam recruitment. This effect is probably a necessary 

 price to pay for the harvest of the adult, marketable 

 clams. Inside seagrass beds, effects of clam kicking 

 on seagrass biomass and bay scallop abundance are 

 quite serious and long-lasting. Because seagrass con- 

 tributes so substantially to the production of many 

 coastal fisheries (Thayer et al. 1985), any regulation 

 that might limit the intensity of clam fishing in that 

 habitat would probably be beneficial. Restriction of 

 the much more efficient mechanical clam harvesters 

 to unvegetated bottoms may be a suitable mech- 

 anism for limiting the total harvest pressure in 

 seagrass beds and, thereby, preserving other fish- 



296 



