FISHERY BULLETIN: VOL. 79, NO. 1 



(Helfman 1979). This position is strengthened by 

 the more clearly defined behavior in the Califor- 

 nian representatives of tropical families. But at 

 least two considerations complicate this compari- 

 son. First, activity patterns, no matter how highly 

 structured, will be less evident in temperate fish 

 communities because a greater proportion of the 

 species there are sedentary. As stated for tropical 

 fishes (Hobson 1972), relative activity in sedentary 

 species is difficult to quantify. Second, and perhaps 

 more important, because there are far fewer 

 species in the temperate habitats, community ac- 

 tivity patterns will be less distinct if only because 

 they are defined by fewer forms. It need not follow 

 that activities of each species are less structured. 

 Despite these cautions, however, it is generally 

 accepted that organisms tend to have less 

 specialized habits where species are fewer, and 

 this circumstance should produce more loosely 

 structured activities. 



Whether or not activities of individual species 

 are less structured in California than in the 

 tropics, certainly the overall community patterns 

 in California are less clearly defined. In examin- 

 ing the changeovers between diurnal and noctur- 



nal modes, for example, we found little evidence of 

 the detailed community transition-patterns that 

 tj^ically characterize these phenomena on tropi- 

 cal reefs (Hobson 1972; Collette and Talbot 1972; 

 Domm and Domm 1973; McFarland et al. 1979). In 

 particular, we were unable to clearly define a 

 "quiet period," that 15-20 min segment of twilight 

 on many tropical reefs when smaller fishes — both 

 diurnal and nocturnal — have vacated the water 

 column. Based on studies in the tropics (Hobson 

 1968a, 1972; Munz and McFarland 1973), the quiet 

 periods are considered times of increased danger 

 from predators when smaller fishes find it adap- 

 tive to avoid exposed positions. So if the quiet 

 periods are less evident in California, it could indi- 

 cate reduced crepuscular predation there. 



When the sequence of twilight events identified 

 at Santa Catalina Island is related to the timing of 

 the quiet period at Kona, Hawaii (Figure 13), there 

 might appear to be more overlap between the 

 diurnal and nocturnal modes in California. For 

 instance, as the nocturnal juveniles of Sebastes 

 serranoides move into exposed locations (Figure 

 13, event 5), they sometimes pass above active lab- 

 rids (Figure 13, events 2, 3, and 4) and close to the 



'I KONA QUIET PERIGD^I 



Si 



H^ 



m 



m 



I CIVIL TWILIGHT 



' KONA CAT. 



Jl± 



^ 



2JI 



NAUTICAL TWILIGHT 

 KONA CAT. 



Sunset 10 20 30 40 



TIME IN MINUTES 



50 



60 



Figure 13. — Events during the evening changeover between day and night at one southern Califomian site from August to November 

 1973, relative to timing of the quiet period at Kona, Hawaii ( Hobson 1972) . ( The Califomian site is illustrated in Hobson and Chess 1976: 

 fig. 2, 3.) Circles represent diurnal species, diamonds represent nocturnal species. Event 1 is based on estimates, events 2-7 on counts, 

 with bars encompassing range, and numbers located at mean. 1. Migration of Chromis punctipinnis to nocturnal resting area: 

 progressive disintegration of bar represents decreasing numbers of individuals in migrating groups (n = 6). 2. Time last Oxyjulis 

 californica was seen active (n = 4). 3. Time last Halichoeres semicinctus was seen active (n = 6). 4. Time last Semicossyphus pulcher 

 departed observation site for nocturnal resting places elsewhere (n =4). 5. Time first Sebastes serranoides appeared at open water 

 feeding ground (« = 5). 6. Time first Xenistius californiensis arrived on feeding ground (n = 4). 7. Time first Seriphus politus arrived on 

 feeding ground (n = 4). Times of civil and nautical twalight are from Nautical Almanac (U.S. Naval Observatory, Washington, D.C.) and 

 are means of times on dates observations were made. 



22 



