DAY VERSUS NIGHT ACTIVITY OF REEF FISHES IN 

 A KELP FOREST OFF SANTA BARBARA, CALIFORNIA 



Alfred W. Ebeling and Richard N. Bray' 



ABSTRACT 



Vertical distributions and feeding activities of residential kelp-bed fishes were compared between day 

 and night in an area of reef and kelp off Santa Barbara, Calif. Abundances and positions of fishes within 

 four vertically oriented zones were obsen-ed during 42 paired day and night scuba transects made 

 throughout the year along a line secured to a high-relief rocky reef located about 1.6 km offshore. 

 Feeding activity was determined for surfperches (Embiotocidae) from the proportion of fish collected 

 during the day or night having empty "foreguts" and inferred for other fishes from general 

 observations of individuals. Although almost all of the 25 common fish species recorded were seen both 

 day and night, the number seen and the degree of activity of most of these species decreased 

 considerably at night. Many fishes that fed and moved about in mid-water well above the reef during 

 the day were found in holes and crevices in the reef at night; others that foraged on or just above the 

 bottom during the day showed little change in their position; and still others tended to disperse to 

 adjacent areas of the reef. Daytime aggregations of fishes centered around the crest of the reef and 

 other productive prominences and invariably dispersed at night. Unlike tropical communities of reef 

 fishes, the kelp-bed community included neither a broad replacement for diurnal planktivores in the 

 night shift nor a contingent that moves out over nearby sand flats to forage at night. Kelp-bed fishes 

 showed considerable intraspecific variability in behavior. Thus, the kelp-bed community appears to be 

 more loosely "programmed" even though it follows the same basic pattern of diel activity as the 

 tropical-reef community. The kelp-bed species that belong to primarily tropical families tended to be 

 quite specialized in their nocturnal sheltering behavior. Yet the primarily temperate surfperches, for 

 example, simply became somewhat lethargic and remained exposed at night. 



Day-night variations in the activities of reef 

 fishes have received considerable attention 

 recently, especially as these variations may relate 

 to foraging methods (Hobson 1975), and to sharing 

 of limited space (Smith and Tyler 1972). Direct 

 observations of coral reef fishes have shown that, 

 although most species are active mainly during the 

 day, a substantial number are active only during 

 the night (Hobson 1965, 1968, 1974; Starck and 

 Schroeder 1965; Smith and Tyler 1972). In both 

 instances, fish forage mainly during their active 

 periods and school and/or seek shelter during their 

 inactive periods (Hobson 1972). Dawn and dusk are 

 important transitional periods when fishes that 

 had been active seek shelter, when fishes that had 

 been resting begin foraging, and when piscivores 

 become most effective (Hobson 1972; Collette and 

 Talbot 1972; Domm and Domm 1973). 



The assemblage of fishes at a particular place on 

 a tropical reef at night may differ markedly from 

 the assemblage gathering at the same place dur- 

 ing the day because foraging and sheltering 



'Marine Science Institute and Department of Biological 

 Sciences, University of California, Santa Barbara, CA 93106. 



activities do not always occur in the same area. For 

 example, some surgeonfishes (Acanthuridae) and 

 damselfishes (Pomacentridae), which shelter at 

 night in the shallower portions of coral reefs, 

 migrate offshore at dawn to their feeding grounds 

 in deeper water (Hobson 1972). Nocturnal preda- 

 tors may undergo even more extensive migra- 

 tions. Some snappers (Lutjanidae) and grunts 

 (Pomadasyidae) are among a considerable number 

 of species that move away from the reef at night 

 to forage over surrounding sand flats (Hobson 

 1968, 1972). For many planktivores, however, the 

 change in activity simply involves vertical 

 movements from foraging areas in the water 

 column to underlying sheltering sites (Hobson 

 1973). Thus the important events during the 

 transition period between day and night include 

 vertical as well as horizontal movements of fish. 



Less is known about the nocturnal activities of 

 temperate kelp-bed fishes. Some information has 

 been available on a few species: the garibaldi, 

 Hypsypops rubicundus (By Clarke 1970); the 

 California sheephead, Pimelometopon pulchrum 

 (by Wiley 1974); the kelp perch, Brachyistius 

 frenatus; white seaperch, Phanerodon furcatus, 



Manuscript accepted April 1976. 



FISHERY BULLETIN: VOL. 74, NO. 4, 1976. 



703 



