Ecological drivers of spatial variability among fish fauna of 21 tropical Australian estuaries

Abstract

Tropical estuarine fish assemblages often show characteristic spatial variation at the scale of individual estuaries but there is no clear grouping of estuaries based on variables such as proximity or climatic conditions. This study investigates if such spatial patterns occur at more extensive spatial scales and begins to uncover the mechanisms driving these patterns. We sampled 21 estuaries spanning 650 km of the tropical northeastern coast of Australia that comprise 3 climatic zones and 7 discrete regions. The 21 estuaries possessed broadly similar fish assemblages; however, there was considerable variation in the details of faunal composition, species richness and catch per unit effort (CPUE) of individual species. This variation had little to do with an estuary's proximity to other sites or its climatic zone but was focussed at the estuary-to-estuary scale. The variability was largely a product of contrasting spatial patterns displayed by different species. In turn, the complex assemblage and species patterns seemed to be influenced in complex ways by contrasting responses to physical and ecological variables, with estuary-level ecological variables generally having greater power in explaining faunal differences than site-specific physical variables. The fact that estuary-level ecological variables produced a good explanation of the complex spatial patterns typical of tropical estuar-ine fauna indicates the value of developing estuary-scale explanatory variables that relate to specific ecological processes. The lack of any clear influence of climatic zone or proximity to other sites on spatial patterns highlights the continual need for careful evaluation of paradigmatic understanding. © Inter-Research 2009.