The trophic ecology of caridean shrimps in an eelgrass community

Abstract

Four species of caridean decapods together represent a productive elements of the epifauna of eelgrass beds in Western Port, Australia. The guild is dominated by a palaemonid species, Macrobrachium intermedium Stimpson, which was found to have a mean annual density of approximately 50 individuals m −2 and an annual productivity of 3.4 g ash-free dry mass m −2. Analyses of shrimp diets indicated that three species, M. intermedium, Hippolyte caradina Holthuis and Chlorotocella leptorhyncus (Stimpson), are consumers of both animal and plant material, while a single (crangonid) species, Pontophilus intermedius (Fulton and Grant), is a specialized carnivore. Predation by shrimps may be responsible for the removal of substantial proportions of the productivity of cohabiting smaller invertebrates such as gastropod molluscs, peracaridean crustaceans and polychaetes, and probably eclipses the level of predation by fish. Plant detritus (along with associated microorganisms) is more prominent in shrimp diets during winter, and may be correlated with a reduced availability of animal prey during this period. Shrimps are consumed by a number of the common predatory fish and birds associated with eelgrass flats. Predation is concentrated on the two numerically dominant carideans and may be an important factor modifying the population structure of these species. It is concluded that the Caridea occupy a key position in trophic processes within the eelgrass system by (i) exerting a strong influence on the structure and dynamics of the lower trophic levels of the system; and (ii) by transferring a major proportion of their relatively high productivity to higher consumers.