Spatial and temporal variation in nearshore fish and macroinvertebrate assemblages from a temperate Australian estuary over a decade

Abstract

Nearshore fish and macroinvertebrate assemblages of the Port River-Barker Inlet estuary, South Australia, were sampled by beach seine at monthly intervals between January 1985 and December 1994. Multivariate analyses were used to determ~ne patterns in species distribution and abundance, to determine the influence of site, month and year on assemblage structure, and to identify trends in species composition over the decade. A total of 403626 individuals representing 56 species were recorded, with Aldrichetta forsteri, Hyporhamphus melanochir, Sillaginodespunctata and Pelates octolineatus responsible for 7 6 % of the total abundance. Estuarine-opportunistic species were consis- tently dominant over the decade w ~t h marine stragglers and estuarine-dependents important in some years only. Abundances of the 19 species determined to be dominant varied between years, w ~t h some species, e.g. Spratelloides robustus, Hyporhamphus regularis, Arenigobius bifrenatus, Nesogobius sp. 3 and Cristiceps austrahs, demonstrating considerably greater inter-annual variability compared with others, e.g. S. punctata, A. forsteri, H. melanochir, P. octolineatus, Haletta semifasciata and Sillago schomburgkii. The importance of temporal scale in any assessment of community stability is re-stated; although individual species varied in abundance between months and years, assemblage structure was shown to be reasonably stable over the decade. Water temperature and salinity were weakly correlated with patterns in species composition and abundance. Further experimental studies are required to improve ecological understanding of the system's fish fauna and on-going monitoring is necessary to assess future changes to fish populations in relation to adjacent wetland developments.