Potential for between-mudflat movement and metapopulation dynamics in an intertidal burrowing amphipod

We evaluated the potential for between-mudflat dispersal of individuals of the burrow-dwelling amphipod Corophium volutator. We first estimated the distances travelled by measuring vertical distribution of swimmers in the water column and their activity in relation to the tidal cycle. We found amphipods were located high over the substratum (up to 4 m) with little vertical structure, and swimming occurred during periods of maximum water velocity (large peak during flood tide). Based on the behaviour of amphipods and information on hydrodynamics, we estimated that an individual could move between 0.4 and 14.4 km toward the upper part of the bay in a single swimming event. This distance is sufficient to allow travel from one mudflat to the next in only a few swimming steps. To identify potential migration routes, we also sampled along a shore (covered in a narrow band of mud) between 2 major mudflats. Patterns in density suggested there was a presence of a travelling wave of individuals, which is consistent with predictions made from their swimming behaviour. We evaluated the possibility that C. volutator in the upper Bay of Fundy are found in one or several metapopulations, where the large and discrete mudflats are connected by the dispersal of individuals. We propose a refined, spatially structured population model (modified from terrestrial metapopulation models) applicable to soft sediment environments in marine intertidal zones, in which several groups of a few intertidal flats are connected by the unidirectional movement of the amphipods. The dynamics will largely be determined by the detailed spatial arrangement of intertidal flats and corridors, as well as by the details of the hydrodynamic conditions and behaviour of organisms.