The ecological significance of the combtoothed blenny in a coral reef ecosystem K. A. T OWNSEND *†‡ AND I. R. T IBBETTS ‡ *Moreton Bay Research Station, The University of Queensland, P. O. Box 138, Dunwich, Queensland, 4183, Australia and ‡Centre for Marine Studies, The University of Queensland, St Lucia, Queensland, 4072, Australia (Received 15 April 2003, Accepted 17 March 2004) At Heron Island reef, Great Barrier Reef Australia, biomass densities and mean wet mass of Ward’s damselfish Pomacentrus wardi and the jewelled blenny Salarias fasciatus were not significantly different at 237 v.295gm 2 and 87 v.79 g, respectively. Whereas S. fasciatus significantly exceeded P. wardi in (1) total number of bites per day (3427 v. 1155), (2) the mass of epilithic algal community consumed per bite (219 v.014mg) and (3) total organic carbon consumed per day (48731 v. 3546 mg C m 2 day 1 ). Territorial behaviour differed also between the two species. Pomacentrus wardi chased from their territories a smaller proportion of blennies than roving grazers (i.e. scarids, acanthurids, siganids and pomacentrids) relative to S. fasciatus. Salarias fasciatus chased c. 90% of other blennies from their territories, while chasing only c. 20% of all damsels that entered. Both P. wardi and S. fasciatus rarely chased non-grazers. The chasing behaviour of S. fasciatus was size dependent, with resident fish chasing only individuals of its own family (i.e. Blenniidae) that were the same or smaller size. Pomacentrus wardi may have tolerated S. fasciatus grazing within its territory, as it contributes to territory defence from other blennies. The possibility that the interaction between the two species is facilitative, rather than competitive, is discussed. It was concluded that salariine blennies play an important, and previously under- estimated role in coral reef trophodynamics. # 2004 The Fisheries Society of the British Isles Key words: behaviour; Blenniidae; coral reef fishes; EAC; Pomacentridae; territorial grazers. INTRODUCTION Grazing fishes are important to the health of coral reefs. As consumers of primary production, they are a vital link to the other members of the food chain (Choat, 1991; Polunin & Klumpp, 1992). They also influence benthic community structure on both small and large scales (Ogden & Lobel, 1978; Sammarco, 1980; Hatcher, 1981; Horn, 1989; Carpenter, 1990; Petraitis, 1990). Members of the Pomacentridae, Scaridae, Siganidae and Acanthuridae have been described as keystone grazers in Indo-Pacific reef systems (Choat, 1991). A recent study of the biomass and distribution of herbivorous combtooth blennies (Blenniidae, Salariini) indicated that they may play an important role in the †Author to whom correspondence should be addressed. Tel.: þ617 3409 9058; fax: þ617 3409 9839; email: kathy.townsend@uq.edu.aus Journal of Fish Biology (2004) 65, 77–90 doi:10.1111/j.1095-8649.2004.00426.x, available online at http://www.blackwell-synergy.com 77 # 2004 The Fisheries Society of the British Isles