EBELING and BRAY: ACTIVITY OF REEF FISHES 



or near the bottom. Hyperprosopon argenteum 

 was an exception in tliat individuals of this species 

 occurred alone or in small, loose groups in mid- 

 water at night. Hobson and Chess (1976) and Bray 

 (unpubl. data) found that guts of specimens 

 speared at night were full of recently ingested 

 prey, whereas almost all guts from individuals 

 speared during the day were empty. However, the 

 fact that this fish constitutes a large portion of the 

 catch made by shore fishermen (Frey 1971) in- 

 dicates that at least some individuals feed during 

 the day. 



We know little about the feeding periods of the 

 remaining six species seen along the transect line. 

 The half moon, Medialuna calif orniensis, often 

 appeared to be more sensitive to our presence than 

 were individuals of other species near the bot- 

 tom, and we cannot deny the possibility that 

 Medialuna feeds at night. It reportedly eats 

 mainly algae supporting a variety of attached 

 epiphytic animals and much smaller quantities of 

 free animals (Quast 1968b; FoUett et al. 1960). The 

 fact that two small demersal species, Coryphop- 

 terus nicholsii and Oxylehius pictus, were seen 

 much less often at night suggests that they retreat 

 deep into holes and crevices then. Larger in- 

 dividuals of lingcod, Ophiodon elongatus; Parala- 

 brax clathratus; and S. mystinus eat cephalopods 

 as well as fishes and other prey (Love 1974; Miller 

 and Geibel 1973; Quast 1968c), so it is reasonable to 

 suspect that they too feed, at least occasionally, at 

 night. 



DISCUSSION 



During the day, large numbers of fishes pervade 

 the study area of reef and kelp off Santa Barbara. 

 Most fishes inhabit the mid-water zone well off the 

 bottom, while smaller numbers of ambusher-type 

 predators remain in contact with the reef bottom. 

 In contrast, the same kelp forest appears almost 

 abandoned at night. Most notably, large numbers 

 of fishes disappear from mid-water, while the 

 numbers of fishes increase markedly in the shelter 

 zone of holes and crevices. 



Although day-night changes in fish abundance 

 may be partly attributable to sampling error 

 caused by our use of lights at night, etc., these 

 changes most certainly reflect differences in the 

 fishes' requirements and distributional patterns 

 between their periods of activity and inactivity. 

 During the day, the area in the vicinity of our 

 transect line seems to constitute a focal point of 



fish activity. Daytime fish diversity and abun- 

 dance appeared to be greater along the transect 

 line than in adjacent areas, 5 to 10 m away. Loose 

 aggregations of juvenile 5. mystinus and, less 

 frequently, Chromis punctipinnis, P. clathratus, 

 and Girella nigricans, formed in the water column 

 above the transect line. Likewise, other fishes 

 gathered closer to the bottom. Perhaps this local 

 richness relates to the position of the transect 

 about the reef crest. The transect line was at- 

 tached to one of the highest rocky prominences on 

 the reef, and it ran along the inner margin of a 

 dense stand of giant kelp. Quast (1968a) noted that 

 the combination of high-relief rocks and kelp 

 augments the surface area available for inverte- 

 brates, the principal food of the fishes, and serve as 

 orientation points for fishes throughout the water 

 column. Also, inshore and offshore margins of kelp 

 beds often demonstrate the "edge-effect," in that 

 the fauna is richer there than in areas on either 

 side (Feder et al. 1974). At Naples Reef, surf- 

 perches, especially individuals of Embiotoca later- 

 alis and Phanerodon furcatus, tend to congregate 

 about the reef crest and the south dropoff 20 m 

 away where thick stands of Gelidium and other 

 red algae flourish. Individuals of E. lateralis gorge 

 themselves on the caprellid amphipods that occur 

 in great numbers amongst the algae (Robert 

 Cowen and David Laur, pers. commun.). Also we 

 noticed that fishes tend to aggregate in sunlit 

 areas like the reef crest and avoid the shaded areas 

 on either side. In tropical reefs, diurnally schooling 

 fishes that migrate to adjacent sand flats at night 

 return in daylight to the same prominent topo- 

 graphic features on the reef (Hobson 1973). Other 

 factors that influence local fish abundance and 

 diversity are: availability of food (e.g., Hobson 

 1968, 1972, 1974), proximity to shelter (e.g., Low 

 1971; Sale 1972), and the presence of "cleaner" fish 

 that rid larger fish of their ectoparasites (Slobod- 

 kin and Fishelson 1974). At least some of these 

 factors may also have contributed to the high 

 numbers of fish along our transect line. 



After dark, fishes that seek shelter and/or 

 become inactive are no longer attracted by richer 

 feeding grounds and orientation points charac- 

 teristic of the reef crest. As darkness falls, mid- 

 water aggregations of C. punctipinnis, Parala- 

 brax clathratus, Girella nigricans, and young S. 

 mystinus dissolve as the fish disperse singly or in 

 small groups over the bottom to shelter in the 

 many holes and crevices in surrounding areas. 

 During the day, for example, individuals of C. 



711 



