BECKER and CHEW: PREDATION ON CAPITELLA SPP. 



night indicates that when rex sole were feeding 

 most intensely, selection of Capitella spp. was at 

 its highest level. 



Dover sole was the least selective of the three 

 fishes with respect to predation on Capitella spp. 

 This species did not exhibit selective predation 

 based on prey number during afternoon, nor 

 based on prey size during evening. In addition, 

 the percent dietary contribution by Capitella s^tp. 

 for Dover sole was the smallest of the three fishes 

 during three of the four time periods. The ob- 

 served minimum level of feeding intensity at 

 night is consistent with the description of Dover 

 sole as a diurnal forager (Allen 1982; Becker 

 1984). The nighttime peak in percent dietary con- 

 tribution by Capitella spp. suggests that even 

 though this fish normally does not forage at 

 night, Capitella spp. could be captured quite suc- 

 cessfully relative to other benthic invertebrates. 



English sole was intermediate between rex sole 

 and Dover sole with respect to degree of selective 

 predation on Capitella spp. Although this species 

 selectively consumed these polychaetes based on 

 prey number throughout the diel cycle, prey size 

 selection was not observed during evening. In ad- 

 dition, dietary contribution by Capitella spp. for 

 English sole was the smallest of the three fishes 

 during morning, but intermediate in magnitude 

 during the remainder of the diel cycle. The ob- 

 served peak in feeding intensity at night is con- 

 tradictory to the description of English sole as a 

 diurnal forager (Allen 1982; Hogue and Carey 

 1982; Becker 1984). Because dietary contribution 

 of Capitella spp. peaked at a high level of 73% at 

 night, much of the ability of English sole to forage 

 at night resulted from predation on these poly- 

 chaetes. The influence of Capitella spp. on noctur- 

 nal foraging by English sole was confirmed by the 

 comparison of diel variation of feeding intensity 

 in habitats with and without Capitella spp. 



The observed diel variations of predation on 

 Capitella spp. could have resulted from behav- 

 ioral differences of either the fishes or the poly- 

 chaetes. Because the fishes were sampled 

 throughout the diel cycle, much of the variation 

 due to the predators was accounted for. However, 

 because diel variation in behavior of Capitella 

 spp. could not be evaluated using the sampling 

 methods employed in this study, variation in prey 

 availability is unknown. However, at least one 

 pattern is suggested. Because dietary contribu- 

 tion by Capitella spp. peaked at night for all three 

 fishes, these polychaetes may become more active 

 at the sediment surface and thus more vulnerable 



to predation at night. The ability of English sole 

 to alter its normal diurnal feeding chronology to 

 forage primarily on Capitella spp. at night further 

 suggests that these polychaetes become more ac- 

 cessible at night. Levinton (1971) found that the 

 bivalve Macoma tenta foraged primarily at night 

 and suggested that this periodicity was used, in 

 part, to avoid diurnal predators (primarily winter 

 flounder, Pseudopleuronectes americanus). Al- 

 though this defense mechanism may succeed with 

 obligate diurnal predators, it would not be effec- 

 tive in avoiding nocturnal predators (e.g., rex 

 sole) or species capable of modifying their normal 

 diurnal feeding chronology (e.g., English sole). 



From an applied standpoint, results of this 

 study have several implications regarding the 

 concept of disturbance management described by 

 Rhoads et al. (1978). Those authors suggested 

 that by properly managing habitat disturbance 

 (i.e., dredge-spoil disposal in their case), benthic 

 invertebrate assemblages can be maintained in 

 the early successional stages when they are dom- 

 inated by pioneering species, including oppor- 

 tunists such as Capitella spp. Because productiv- 

 ity of these early successional stages generally 

 exceeds that of later stages, Rhoads et al. (1978) 

 hypothesized that benthic assemblages domi- 

 nated by pioneering species represent an en- 

 hanced food resource for demersal fishes. The ob- 

 served importance of Capitella spp. as prey for the 

 three fishes considered in the present study sup- 

 ports this hypothesis. For example, all three 

 fishes selectively preyed upon Capitella spp. 

 throughout all or most of the diel cycle, and Eng- 

 lish sole was able to modify its normal diurnal 

 feeding chronology to prey primarily on these 

 polychaetes at night. 



Although the hypothesis of Rhoads et al. (1978) 

 is supported by the present study, enhancing the 

 productivity of a food resource may not be benefi- 

 cial to demersal fishes if the nutritional quality of 

 their diet is reduced in the process. For example, 

 a variety offish diseases have been attributed, in 

 part, to dietary deficiencies or imbalances of 

 specific nutrients (reviews in National Research 

 Council 1977, 1981). In addition, the toxicity of 

 chemical contaminants to fishes may be enhanced 

 as a result of improper diets (e.g., Mehrle et al. 

 1977). Although Capitella spp. accounted for only 

 25.7% of the benthic invertebrates sampled in the 

 present study, the dietary contributions of these 

 polychaetes generally were much greater, espe- 

 cially for rex sole. Given the influence of a bal- 

 anced diet on fish health, it is possible that pro- 



477 



