Temporal Changes in the Vagile Epibenthic Fauna of Two Seagrass Meadows (Zostera capricorni and Posidonia australis)

Abstract

The species richness, species composition, and abundance of species in samples of fish, crustaceans, and cephalopod molluscs were examined from samples collected from two monospecific seagrass meadows, Posidonia australis and Zostera capricorni. An analytical strategy is presented whereby the fauna were examined holistically by their full distribution of relative species occurrences and abundances. – Significant differences were demonstrated in both species composition and species abundance between the two seagrass meadows. Greatest differences in species composition occurred during times of low species richness, greatest differences in abundance during times of increased species richness. Within each year species were more often found, and in greater numbers, in summer than in winter, but annual variability was such that some species occurred so frequently and in as great an abundance in summers of one year as in winters of others. – The fauna of P. australis often contained the most species, and during a time of high salinity many species common to both meadows declined. However, at that time a number of species characteristic of high salinity seagrass habitats showed increased frequencies in P. australis. – It was concluded that the differences in the fauna of the two seagrasses were controlled by external events leading to variable recruitment success. Only during favourable recruitment periods were the numbers of individuals different between the two meadows, whilst differences in species composition were heightened during periods of unfavourable recruitment for the dominant species.