HOBSON ET AL.: CREPUSCULAR AND NOCTURNAL ACTIVITIES OF CALIFORNIA FISHES 



Table 4. — Geographic affinities' of the fishes studied. 



I. Warm-temperate representatives of basically tropical families or 

 genera; species tfiat do not range into ttie colder waters northward 

 from central California. Twelve species: 



Scorpaena guttata Girella nigricans 



Paralabrax clathralus Chromis punctipinnis 



Xenistius californiensis l-lypsypops rubicunda 



Seriphus politus Halichoeres semicinctus 



Umbrina roncador Oxyjulis californica 



Medialuna californiensis Semicossyphus pulcher 



II. Temperate representatives of basically tropical families; species tfiat 

 range widely into the colder waters northward from central California. 

 Two species: 



Atherinops affinis Coryphopterus nichoisi 



III. Warm-temperate representatives of temperate families or genera; 

 species that do not range northward from central California. Five 

 species: 



Sebastes atrovirens Alloclinus holderi 



S. serriceps Gibbonsia eiegans 



Leiocottus liirundo 



IV Representatives of temperate families or genera; species that range 

 widely northward from central California. Eight species: 



Sebastes serranoides Embiotoca jacksoni 



Bractiytstius frenatus Hyperprosopon argenteum 



Cymatogaster aggregata IHeterostichus rostratus 



Damalichthys vacca Pleuronichthys coenosus 



'Based on ranges given in Miller and Lea (1972). 



that the difference may reflect the proximity of 

 Santa Barbara to Point Conception, the northern 

 boundary of the warm-temperate zoogeographic 

 region (Hubbs 1960; Quast 1968; Briggs 1974). 



Certainly there is a strong tropical influence in 

 many of the more clearly defined crepuscular and 

 nocturnal activity patterns among southern 

 Californian fishes. Species with the most distinc- 

 tive patterns tend to be warm-temperate represen- 

 tatives of what basically are tropical families. The 

 three Californian labrids, for example, seek and 

 leave nocturnal shelter at precise times relative to 

 sunset and sunrise, just as their tropical relatives 

 do. And the two Californian pomacentrids shelter 

 under reef cover at night in the same manner as 

 tropical pomacentrids. Similarly, of the species 

 listed above that school inactively by day and dis- 

 perse to feed at night, most represent the predom- 

 inantly tropical families Haemulidae and Sci- 

 aenidae. Clearly these behavior patterns are 

 rooted deeply in their tropical ancestry, and are as 

 characteristic of their kind as the more generally 

 recognized morphological features that define 

 their families. Ebeling and Bray recognized the 

 strong influence that ancestral relationships exert 

 on activity patterns, and distinguished "temper- 

 ate derivatives" from "tropical derivatives." (Un- 

 accountably, however, they considered Paralabrax 

 clathratus and Coryphopterus nichoisi to be of 

 temperate stock, even though the affinities of both 

 are predominantly tropical.) These relationships, 



then, are insightful in understanding how activity 

 patterns are integrated in southern Californian 

 nearshore fish communities. The geographical 

 affinities of the various species (Table 4) are help- 

 ful in gaining an overview of these relationships. 



Because nearshore communities in warm- 

 temperate southern California mix fishes of tem- 

 perate and tropical affinities, it is tempting to 

 interpret behaviors in terms of interactions be- 

 tween these two lineages. Such comparisons are 

 risky. For example, Ebeling and Bray (1976) 

 stated: "It is paradoxical that the 'tropical deriva- 

 tives' . . .persist in their complex . . . shelter-seeking 

 while many primarily temperate fishes remain 

 exposed." We see no paradox here. On tropical 

 reefs, too, many diurnal fishes remain exposed at 

 night, while others seek cover. Size often influ- 

 ences which strategy is used. For example, while 

 smaller acanthurids (surgeonfishes) and 

 chaetodontids (butterflyfishes) generally are shel- 

 tered, larger members of their families often rest 

 exposed (Hobson 1972, 1974). Ebeling and Bray 

 went on to suggest: ". . . the 'tropical derivatives' 

 may . . .compete more successfully against primar- 

 ily temperate species such as surfperches for shel- 

 ter on the reef." This speculation, too, is unsup- 

 ported by our observations. Most of the temperate 

 species involved here are widespread northward 

 (see Table 4, Group IV), well beyond the ranges of 

 the tropical derivatives, and there too they are 

 exposed at night (E. S. Hobson pers. obs.). 



We doubt that nocturnal shelter sites are in 

 short supply on California reefs except under ex- 

 ceptional circumstances. The places we identified 

 as resting sites of Semicossyphus pulcher were 

 just sporadically occupied, which seems an un- 

 likely circumstance if there is strong competition 

 for these sites. But clearly there is a shortage of 

 shelter sites where the diurnal planktivore 

 Chromis punctipinnis is so numerous that at night 

 resting individuals overflow from the rocks and 

 actually pile up on the adjacent sand. Apparently 

 this exceptional situation exists where the zoo- 

 plankters on which this fish feeds are abundant by 

 day, but appropriate nocturnal shelter is limited. 

 Significantly, however, the competition for this 

 shelter appears to be intraspecific. 



A casual appraisal of southern Californian 

 fishes agrees with Ebeling and Bray (1976) that 

 activities among fishes of the kelp-bed community 

 are "... more loosely 'programmed'" than among 

 fishes in tropical reef communities. A similar con- 

 dition has been described for temperate lake fishes 



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