Environmental Biology of Fishes 61: 195–204, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. Resource use by Enneapterygius rufopileus and other rockpool fishes Veronica Silberschneider a,b & David J. Booth a a Department of Environmental Sciences, University of Technology, Sydney, Westbourne Street, Gore Hill, NSW, 2065, Australia b Current address: Fisheries Research Institute, P.O. Box 21, Cronulla, NSW, 2230, Australia (e-mail: silberv@fisheries.nsw.gov.au) Received 9 June 2000 Accepted 27 November 2000 Key words: boulders, habitat complexity, ontogenetic diet shifts, rockpools, shelter availability, Tripterygiidae Synopsis Low-intertidal fish communities, including Enneapterygius rufopileus (Tripterygiidae), were studied in rockpools in Sydney, Australia to consider the role of physical factors and food availability in their distribution and abundance. The rockpool fish community in Sydney was speciose (23 species), of which 35% of individuals were E. rufopileus. Fish abundance and 13 physical and biological parameters were measured in twenty-two rockpools spread among 4 sites. Abundance of E. rufopileus was best predicted by the number of rock overhangs, algal cover (Zonaria sp. and Hormosira banksii), and the encrusting ascidian cunjevoi (Pyura sp.). Experimental increase or decrease in available shelter (mainly boulders and macroalgae) in rockpools did not significantly affect the abundance of fishes, however some pools consistently supported more fishes in total, despite repeated defaunation, indicating that underlying deterministic processes may have a significant effect on rockpool fish communities. The diet of Enneapterygius rufopileus included unidentified crustacean remains, harpacticoid copepods, and gastropods. Gastropod abundance was greater in the diets of larger fish, which also consumed more food overall. Total weight of food was not dependent on E. rufopileus density in pools or the densities of all fish species in pools. Therefore, the study does not support the hypothesis that resources were limiting for this fish species in rockpools. Introduction Shelter and food are major resources that may limit populations of organisms. Shelter, as a refuge from predators, can reduce mortality in fishes (Shulman 1985, Behrents 1987, Hixon & Beets 1989, 1993, Carr 1991, Connell & Jones 1991) and other prey organisms (Woodin 1978, Hixon & Menge 1991). In particular, structural complexity of the habitat can directly affect abundance by providing competitive refuges and/or prey refuges, allowing more species, both competitors and predators, to coexist through spatial partitioning of a limited resource (Behrents 1987, Hixon & Menge 1991, Hixon & Beets 1993). Access to shelter is especially important for small intertidal fishes, many of which are incapable of sustained swimming (Gibson 1982). They avoid cap- ture by predators due to their cryptic colouration, visual alertness and intimate knowledge of their immediate surroundings, allowing them to rapidly enter holes and crevices which are too small for the predator to fol- low (Gibson 1982). This use of shelter in rockpools by intertidal fishes may become more important as high tide approaches since the advancing tide brings in predatory subtidal fishes. Biological factors, such as the amount of macro-algae versus turf algae (Jones 1988) and availability of suitable food (Gibson 1972, Jones 1984), coupled with physical factors, seem to espe- cially influence the structure of rockpool communities. Shelter can also provide a refuge from the physical stresses occurring in exposed rockpools, such as tem- perature and wave action. Temperature in algae and