Amphipods, isopods and surface currents: a case for passive dispersal in the Bay of Fundy, Canada

Abstract

Six species of isopods and 18 species of amphipods were collected in the neuston of the Bay of Fundy and adjacent waters. Collections were made over a grid of stations covering 2.4 .times. 104 km2 during three spring, three summer and two autumn surveys. No isopods and only five species of amphipods were found in spring surveys. Isopods and amphipods were diverse and plentiful in the neuston in summer and autumn. Dominant isopods were Idotea baltica and I. metallica, and dominant amphipods were Calliopius laeviusculus and Parathemisto gaudichaudi. Amphipods and isopods reach the neuston of the Bay of Fundy in three ways. Idotea metallica, the only euneustonic species present, was probably advected into the Bay of Fundy from southern waters in summer, and did not appear to overwinter in the Bay. Most species, including J. baltica, were collected with drifting littoral vegetation, and we suggest that transport by surface currents is an important factor in dispersal of some shoreline crustaceans. Midwater plankton, such as Parathemisto gaudichaudi, reached the neuston either by advection in upwelling waters or by an extension of their normal diel vertical distribution.