THE INFLUENCE OF HABITAT STRUCTURE ON NEARSHORE FISH ASSEMBLAGES IN ASOUTHERN AUSTRALIAN EMBAYMENT - COMPARISON OF SHALLOW SEAGRASS, REEF-ALGAL AND UNVEGETATED SAND HABITATS, WITH EMPHASIS ON THEIR IMPORTANCETO RECRUITMENT

Assemblage structure and juvenile recruitment of fishes was compared a mongst three habitats: seagass, Heterozostera tasmanica (Martens ex As chers.) den Hartog; reef-algal; and unvegetated sand. Sampling was con ducted monthly from October 1993 to March 1994 at three locations in P ort Phillip Bay, southern Australia. A fine-mesh seine net was used to sample subtidally at a depth of approximately 0.5 m. Fish assemblages differed primarily between structured habitats and unvegetated sand, and a number of species previously reported to occur in seagrass habit at were also found to utilise reef-algal habitat. Species richness was highest in seagrass and lowest in unvegetated sand with significant d ifferences amongst all habitats. Total abundance varied between habita ts depending on location and month examined, but the most common patte rn was highest abundance in seagrass and lowest in unvegetated sand, w ith a significant difference only between seagrass and unvegetated san d. At the level of individual taxa, pipefishes of the genus Stigmatopo ra showed a strong preference for seagrass habitat from an early juven ile stage. The King George whiting, Sillaginodes punctata (Cuvier and Valenciennes), showed a complex relationship with habitat, occurring o n both seagrass and reef-algae immediately after settlement, but, with growth, showing an increasing preference for reef-algae before finall y shifting to unvegetated sand approximately 4 months after settlement . Other species previously found as juveniles on seagrass beds also re cruited to reef-algal habitats. Strong locality effects were also foun d, particularly for King George whiting. This variation was unlikely t o be related to habitat structure, because macrophyte biomass showed m uch greater variation within locations than amongst locations. We conc lude that while the presence of structure per se is sufficient for the recruitment of many species, some taxa will discriminate amongst habi tats based on structural characteristics. (C) 1998 Elsevier Science B. V.