EBELING ET AL.: ANNUAL VARIABILITY OF REEF FISH 



because of greater evenness, maintained a more 

 constant species composition than the mainland- 

 bottom assemblage. But there is no good basis, 

 either theoretical (May 1973) or empirical, for as- 

 suming that this relation is a causal one. Some 

 diverse communities of coral-reef fishes are 

 reportedly not stable at all; in fact, fluctuations in 

 their species composition may actually increase 

 their diversity (Sale 1977, 1978; Talbot et al. 

 1978). 



Rather, both constancy and diversity of the as- 

 semblages are probably determined by the type of 

 habitat in which they live. Thus, the relatively low 

 diversity and high temporal instability of the 

 canopy assemblages probably reflect the simplic- 

 ity and instability of the canopy habitat. Most fish 

 meet in the canopy to eat plankton or planktivo- 

 rous fishes. In this way, the canopy habitat is a 

 concourse, where animals meet for one purpose 

 (Elton 1927; Whittaker 1965). Here there are rela- 

 tively few opportunities for diversifying form and 

 function, and hence fewer species. Relatively few 

 environmental factors strongly influence species 

 distributions, as May (1975) suggested in general 

 for simply structured communities. Ephemeral 

 currents, turbidity, temperature, and kelp growth 

 may influence the distribution of canopy dwellers. 

 Bray (1978) has showTi that the distribution of 

 adult blacksmith is strongly affected by food- 

 bearing currents. Adults have largely indepen- 

 dent sources of food and shelter: the reef provides 

 shelter but water currents carry in their 

 planktonic food. Blacksmith feed in dense aggre- 

 gations, and since local oceanographic conditions 

 fluctuate rapidly (Quast 1968a) and plankton oc- 

 curs in patches (Wiebe 1970), the location of their 

 optimal area of foraging frequently shifts. 



In contrast, our bottom assemblages depend on 

 more stable commodities like rocks and infaunal 

 prey, which are not so immediately affected by 

 factors, like currents, that change rapidly. Many 

 bottom species are solitary, parochial, or even ter- 

 ritorial (Clarke 1970; DeMartini 1976; Larson 

 1977; Hixon 1979). Thus, their local density is not 

 so likely to change from day to day. 



The greater variability of the mainland-bottom 

 assemblage than that of the island is curious. 

 Perhaps the relative isolation of the mainland site 

 may contribute to vagarious settlement offish lar- 

 vae and other recruitment (Larson 1977). Also, the 

 mainland site has relatively large areas of reef flat 

 and a surrounding plain of sand and cobble, creat- 

 ing more of a "transitional" type of habitat. 



Periodic occurrences of such species as the black 

 croaker, Cheilotrema saturnum, and rainbow 

 surfperch, which are atypical of continuous high- 

 relief rocky habitats, lend discontinuity to the 

 Naples fish assemblage. 



ACKNOWLEDGMENTS 



We thank Milton Love for help in taking and 

 viewing cinetransects. Norm Lammer provided 

 much technical assistance with equipment and 

 boating operations. We appreciate use of the 

 UCSB Channel Island Field Station, through the 

 kindness of Carey Stanton who provided access, 

 and of the U.S. Navy, Port Hueneme who provided 

 transport. This work was sponsored by NOAA, 

 Office of Sea Grant, Department of Commerce, 

 under grant no. 2-35208-6 and 04-3-158-22 (Pro- 

 ject R-FA-14); by NSF Sea Grants GH 43 and GH 

 95; and by NSF grants GA 38588 and OCE76- 

 23301. Supplementary funding was provided by a 

 UCSB Faculty Research Grant (No. 369) for com- 

 puter time and by the Marine Science Institute 

 through the courtesy of Henry Offen. 



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