Factors associated with variations in abundance of epifaunal caridean shrimps between and within estuarine seagrass meadows

Abstract

The patterns of abundance of epifaunal caridean shrimps in seagrass meadows of the Hopkins River estuary, south-western Victoria, Australia were described, and environmental factors that best explained abundance patterns were sought at two scales: within and between meadows. The abundances of the three species, Macrobrachium intermedium, Paratya australiensis and Palaemon serenus, were strongly related to the position of meadows within the estuary. Patterns of abundance between meadows were likely to be determined by distribution of larval recruits, and extent of post- larval migration, both between meadows and to and from stocks outside the estuary (the river upstream for Paratya, and adjacent coastal waters for Macrobrachium and Palaemon). Variation in caridean abundances over 1 year was related to temperature and salinity. Patterns of recruitment and migration could in part be explained by physiological responses to physico-chemical changes. However, it is hypothesized that competitive exclusion from preferred deeper parts of meadows is a trigger for migration of Paratya from the estuary. Although caridean densities within some meadows were at times correlated with seagrass biomass, patterns of seagrass abundance did not explain between-meadow patterns of caridean abundance well.