Fish community structure and distribution in a macro-tidal inshore habitat in the Irish Sea

Estuaries, lagoons and mudflat habitats represent a crucial biodiversity component in coastal waters and may act as vital nurseries and shelters for the juvenile stages of many commercial fish species. A study of the spatial distribution of inshore fish fauna around the shallow coastal habitats of North Bull Island (Dublin Bay, Ireland) was carried out during summer and autumn of 2005, in order to characterise the fish community present therein. Four stations were examined, situated along a putative environmental gradient, between the mudflat and the open sea shore. Stations were surveyed at both high and low tide and sampling was repeated weekly for eight weeks, spanning over four spring and four neap tidal events. A total of 17 fish species were caught, belonging to 13 families. The community was largely dominated by the lesser sandeel (Ammodytes tobianus) and the common goby (Pomatoschistus microps). Ordination techniques were used to generate hypotheses as to the general patterns in the fish community; Shannon–Wiener index was employed to estimate spatial, temporal and tidal trends in diversity; and analysis of variance (ANOVA) was employed to test for the influence of time of the year, habitat, tidal phase and tidal state on the spatial distribution of fishes. Results reveal that time of the year and habitat variation across the environmental gradient are the major factors in determining fish community structure. The influence of tidal dynamics seem to have a lesser impact on the overall community, but can significantly and variably affect the distribution of individual species.