DIET, FOOD PREFERENCE, AND ALGAL AVAILABILITY FOR FISHES AND CRABS ONINTERTIDAL REEF COMMUNITIES IN SOUTHERN CALIFORNIA

Herbivory by wide-ranging fishes is common over tropical reefs, but ra re in temperate latitudes where the effects of herbivorous fishes are thought to be minimal. Along the west coast of North America, herbivor y by fishes on nearshore reefs is largely restricted to a few members of the Kyphosidae, distributed south of Pt. Conception. This paper pre sents information on natural diets and results from feeding choice exp eriments for two abundant kyphosids from intertidal habitats in San Di ego, California - Girella nigricans and Hermosilla azurea, and similar data for the lined shore crab, Pachygrapsus crassipes, which also for ages over intertidal reefs. These results are compared with the availa bility of algae in intertidal habitats measured during summer and wint er, on both disturbed and undisturbed habitats. The diets of juveniles of G. nigricans and H. azurea collected from nearshore habitats were dominated by animal prey (mainly amphipods), but adults of these fishe s, and P. crassipes, consumed algae nearly exclusively, with 26, 10, a nd 14 taxa of algae identified from G. nigricans, H. azurea, and P. cr assipes, respectively. Algae with sheet-like morphologies (e.g. Ulva s p., Enteromorpha sp., members of the Delesseriaceae) were the principa l algae in the diets of the fishes, and calcareous algae (e.g. Coralli na sp., Lithothrix aspergillum) and sheet-like algae (Enteromorpha sp. ) comprised the greatest identifiable portion of the shore crab's diet . Feeding choice experiments indicated that the fishes preferred filam entous algae (e.g. Centroceras clavulatum, Polysiphonia sp., Chondria californica) and sheet-like algae (e.g. Enteromorpha sp., Ulva sp., Cr yptopleura crispa) over other algal morphologies, whereas the shore cr ab chose jointed calcareous algae (e.g. Lithothrix aspergillum, Corall ina vancouveriensis, Jania sp.) most frequently. The diets and prefere nces for algae by the fishes were generally most similar to the assemb lage of algae available in early successional (disturbed) habitats dur ing summer when sheet-like and filamentous algae are abundant. The sho re crab exhibited the opposite trend with a diet more similar to late successional (undisturbed) habitats.