FISHERY BULLETIN: VOL. 74, NO. 4 



Figure 2.-Day and night positions of four ecological groups of 

 fishes inhabiting Santa Barbara kelp beds: A) demersal species 

 {Coryphopterus nicholsii, Ophiodon elongatus, Oxylebius pictiis, 

 Sebastes carnatus, S. chrysomelas, S. serriceps, and Scorpaen- 

 ichthys marmoratus); B) large-mouthed generalized predators 

 {Paralabrajc clathratus, Sebastes serranoides, and adult S. 

 mystinus); C) surfperches {Embiotoca jacksoni, E. lateralis, 

 Hypsurus caryi, Pkanerodon furcatus, Rha^ochihis toxotes, and 

 Damalickthys vacca); D) small-mouthed grazing and picking 

 tropical derivatives (Chromis punctipinnis, Hypsypops 

 nibicundus, Medialuna califomiensis, Oxyjulis californica, and 

 Pimelometapon pulchrum). Vertical zones (I-IV) are defined in 

 Table .' Each fish symbol represents 10% of the total individuals 

 in the group expressed proportionally to the relative abundances 

 of the different species in the group. 



tively recent derivatives of primarily tropical 

 families (Pomacentridae, Labridae, etc.), and 

 essentially all show extreme changes in their 

 vertical distribution {\h = 2.07) as they actively 

 seek the shelter zone refuge. Some at least, like 

 Chromis punctipinnis, are specialized to the 

 extent that they tend to "home" to the same hole 

 on successive nights (Bray unpubl. data). 



Thus, in the kelp beds, there is no broad re- 

 placement for the "day shift" of fishes at night, 

 even though the fishes' invertebrate prey appear 

 to be more active and exposed then. And, in 

 general, after the dusk period of intensified ac- 

 tivity, the notably lackluster night life gives the 

 kelp forest an aura of desolation, as compared with 



the pictures of renewed (albeit lessened) activity 

 painted of the community of coral reef and out- 

 lying sand-flat fishes at night (Starck and Davis 

 1966; Collette and Talbot 1972; etc.). Perhaps the 

 relatively clear and well-lighted tropical waters 

 are more conducive to nocturnal activity for the 

 many visually oriented fish. Denied much of the 

 moonlight by the dense kelp canopy and frequent 

 low clouds, the relatively turbid, temperate waters 

 are often a dark and gloomy place at night. In fact, 

 even during the day when the water is particularly 

 turbid, the usually active planktivores, grazers, 

 and browsers tend to stop foraging and often seek 

 shelter, as do their tropical counterparts under 

 similar conditions (Collette and Talbot 1972). 



It is paradoxical that the "tropical derivatives" 

 (Figure 2D) persist in their complex nocturnal 

 shelter-seeking while many primarily temperate 

 fishes remain exposed. One explanation assumes 

 that selection pressures brought about by noctur- 

 nal (or crepuscular) predation are either different 

 or more relaxed in our temperate system of kelp 

 forest and reef than in the tropical reef system. 

 Observing a similar set of circumstances, Hobson 

 (1972) noted that Hawaiian reef fishes, which 

 enjoy a relative dearth of crepuscular predators, 

 show the same specialized sheltering behavior 

 during twilight as do their close relatives in the 

 Gulf of California, which have many such preda- 

 tors. He suggested that these complex behavior 

 patterns may evidence historic selection pressures 

 from predators. These patterns may persist on 

 Hawaiian reefs today even though they are cur- 

 rently perhaps less critical to the survival of the 

 refuge-seeking species than in reef systems else- 

 where. An alternative explanation holds that 

 crepuscular and nocturnal predation by, e.g., the 

 Pacific electric ray, is important in kelp beds, but 

 that the tropical derivatives compete more suc- 

 cessfully against the primarily temperate species 

 for shelter. 



CONCLUSIONS 



As indicated by paired day-night observations 

 along a transect line, kelp-bed fishes occur in about 

 the same relative abundances throughout the year 

 in an area of reef and kelp along the mainland side 

 of the Santa Barbara Channel. During the day, 

 most fishes occupy the "mid-water zone" higher 

 than 1 m off the bottom. Far fewer are "exposed on 

 the bottom" or in the "shelter zone" of holes and 

 crevices in the reef itself. During the night, when 



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