To what extent are the fish compositions at nearshore sites along a heterogeneous coast related to habitat type?

This study has tested the following main hypotheses. (1) The composition of fish assemblages in nearshore waters along the lower west coast of Australia will differ significantly among four habitat types (1–4), which could be distinguished quantitatively from each other by differences in the values for a statistically selected suite of enduring environmental variables. (2) The extents of the differences in ichthyofaunal composition among the four habitat types will statistically match those in the suite of environmental variables that distinguish those habitat types. A 60.5 m long seine net, with 9 mm mesh in the bunt, was used seasonally for 2 years to sample fish from sites representing each of the four nearshore habitat types, which differed broadly in their exposure to wave activity and the extent and location of seagrass beds. The compositions of the fish faunas in each habitat type were significantly different from each other in all but one case. Ichthyofaunal composition did not differ significantly between years in any habitat type and differed significantly among seasons in only one habitat type. The arrangement of the rank orders of similarity in matrices constructed from the abundances of the fish species at each site also did not differ between years but did differ among seasons. Moreover, the arrangement of the ranks in the similarity matrices produced from the ichthyofaunal data recorded at the various sites in each season were significantly correlated with that in the distance matrix constructed from the environmental data for those sites, with the correlation (ρ) ranging from 0.476 in winter to 0.696 in autumn. These results thus demonstrate that the extents of the differences in the fish compositions among the various habitat types parallel those in the environmental data for the corresponding habitat types. The subset of species that provided the best correlation with the environmental distance matrix, and which was thus most responsible for distinguishing among the fish compositions at the four habitat types, was also determined for each season.