HOBSON and CHESS: TROPHIC RELATIONS OF THE BLUE ROCKFISH 



however, reached maximum development during the 

 summer. Prominent among them were benthic 

 algae, e.g., Desmarestia ligulata and Laminaria set- 

 chelli, as well as certain sedentary animals including 

 various sponges, e.g., Leucilla nuttingi; ascidians, 

 e.g., Trididemnum opacum; hydroids, e.g., Obelia 

 spp.; and bryozoans, e.g., Bugula spp. The benthic 

 caprellids and gammarideans attained peak numbers 

 during early summer, when they literally carpeted 

 some areas of the seafloor. Samples taken with an 

 airlift during July 1978 measured densities of over 

 10,000 caprellids (mostly Metacaprella kennerleyi), 

 and 108,000 gammarids (mostly Jassa spp.) in m- 

 quadrats. Their numbers declined sharply during 

 August, however, and by September they occurred 

 only in scattered patches. 



Feeding Conditions 



The diet of S. mystinus relative to foods present 

 during the upwelling season was assessed with 

 samples of gut contents and near-surface plankton 

 taken during 7 upwelling episodes (Table 2) and 10 

 downwelling episodes (Table 3). 



More prey were consumed during the downwell- 

 ing episodes (e.g., x no. prey taken = 110.8, vs. 

 20.1 during upwelling episodes). Thaliacians (Fig. 

 6) were the primary food during the upwelling 

 season, but all were taken during downwelling 

 episodes— the only times when the guts were packed 

 with food. These relatively large, gelatinous zoo- 

 plankters did not occur either in the plankton or in 

 the diet of S. mystinus during upwelling episodes. 



Table 2— Continued. 



'Value is estimated mean number per 100 m^ of water, based on water filtered (54.8 m^) during the 5-min collection. 



2NR = not recorded. The enumeration was either omitted or unfeasible, 



^Velella velella floats on the water's surface, where it was not effectively sampled by our net. 



"Most mysids sampled were Acanthomysis sculpta. 



^Adult S mystinus often were seen feeding on large individuals of Cyanea capillata (Fig. 5), which were avoided by us during plankton 

 collections because they would have made collections unmanageable. 



^According to Kathleen Conlan (National IVIuseum of Canada, P.O. Box 3443, Station D, Ottawa, Canada KIP 6P4, pers. commun. 

 26 f^ay 1 987), Jassa falcata does not occur in California, and forms along the coast considered to be this species (including the form(s) 

 referred to here) are undescribed. 



't^any of the calanoids from the plankton included in this category were juveniles and other undetermined stages of the species 

 distinguished above. Most were at the lower end of the size range indicated. 



^Foods digested beyond recognition. 



723 



