FISH AND DECAPOD CRUSTACEANS INHABITING DRIFTING ALGAE IN JERVIS BAY,NEW-SOUTH-WALES

This study documents the fish and decapod crustaceans inhabiting a bed of Gracilaria verrucosa that was drifting on the bottom of a temperat e marine embayment in relatively deep water (15-18 m) during autumn 19 91. Fauna were sampled with diver-operated enclosure nets. Relatively few species inhabited the algae at this time, and the assemblage was p rimarily a subset of that in adjacent Posidonia australis beds. Three fish species [Neoodax balteatus (Odacidae), Cristiceps australis (Clin idae), Siphamia cephalotes (Apogonidae)] and one species of crab [Nect ocarcinus tuberculosus (Portunidae)] dominated the catches numerically . A further 14 fish and decapod species were relatively rare. Neoodax balteatus, C. australis and N. tuberculosus were caught at all life st ages and appeared to be permanent residents of the Gracilaria. Few juv eniles of other species were captured, which indicates that these alga l wracks may not be an important nursery habitat for seasonally reside nt fish species. Trachurus novaezelandiae and a number of other fish s pecies that associate with a variety of benthic habitats appeared to b e transient visitors. The biomass of algae varied significantly within the bed, but algal biomass was not a good indicator of faunal abundan ces. The low species richness of the fish and decapod crustacean assem blage may be related to both lower recruitment in deeper water and to unfavourable characteristics of the alga.