Temporal population dynamics of the swarming shrimp, Acetes sibogae australis, in a tropical near-shore system

Abstract

Acetes sibogae australis, a small swarming crustacean, is an important component of near-shore systems in eastern Australia. It is considered that densities of A. s. australis are highly variable. However, this variability has never been tested on a fine temporal scale. In this study, densities of A. s. australiswithin swarms, as well as swarm length and width, were recorded once a week for seven months at one locality in Townsville, Australia, and once a fortnight for seven months at two other localities in the region. Length frequency of a sub-sample of individuals caught at each sample time was also recorded. Density of A. s. australis fluctuated significantly during the seven months, with numbers per replicate varying between 0 and 1000 individuals. Swarm width and length were significantly correlated with density, contributing to large-scale differences in overall abundance. Length frequencies revealed at least three dominant cohorts present during the seven months, although appearance and disappearance of these did not correspond to density changes. Patterns recorded were similar at the three spatially separate localities. The large fluctuations in A. s. australis abundance over time are likely to have important effects on the near-shore system of Townsville.