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

Abstract

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. 449: 197-209, 2012 are patchily distributed and exchange individuals, especially through planktonic larval stages. Consequently, such populations are increasingly viewed as metapopulations in the marine ecological literature, although it may not be the most appropriate approach in many cases (Grimm et al. 2003). Marine metapopulations that resemble their terrestrial counterparts (a large number of discrete populations undergoing colonization or extinction dynamics) appear to be rare; examples include copepods in rocky intertidal pools (Dybdahl 1994) and, potentially, giant kelps in shallow coastal waters (Reed et al. 2006). A set of conditions (reviewed in the Discussion) is required for metapopulation models to be more informative than other population models, and these should be assessed before adopting a metapopulation approach (Hanski 1997, Grimm et al. 2003. In systems where a metapopulation approach can be appropriate and informative, marine ecologists will need to incorporate structural differences of the marine environment into the existing body of theory (e.g. spatial arrangement of suitable habitat, means of dispersal of organisms; Kritzer & Sale 2006) before applying these models. KEY WORDS: Marine metapopulation · Soft sediment · Dispersal · Corridor · Coro...

Spatial Variation in Population Structure and Its Relation to Movement and the Potential for Dispersal in a Model Intertidal Invertebrate

“…Studies of swimming behavior in a key mudflat species Corophium volutator led to a better understanding of its population distribution and maintenance [27], [36], [39], [52]. However, the adaptive significance of dispersal in this species remained poorly understood.…”

“…Distinct population structure of swimmers, even for mudflats adjacent to one another, suggests that movement by individuals largely occurs within the boundaries of mudflats. However, high rates of gene flow suggest that dispersing individuals are reaching adjacent mudflats [40]; individuals found in the water column are most likely representative of those individuals dispersing large distances [39].…”

“…C. volutator actively controls its entry and time spent in the water column by swimming, or beating its pleopods [37], [38]. Swimming is also combined with passive movement driven by water currents, with individuals entering the water column during periods of peak velocity in tidal currents [32], [39]. Individuals swimming as high as 4 m into the water column may be transported large distances, up to 14.4 km in a single swimming event [39].…”

“…Swimming is also combined with passive movement driven by water currents, with individuals entering the water column during periods of peak velocity in tidal currents [32], [39]. Individuals swimming as high as 4 m into the water column may be transported large distances, up to 14.4 km in a single swimming event [39]. As a consequence, the genetic structure of C. volutator populations shows high connectivity among mudflats [40].…”

Dispersal of marine benthic invertebrates through ice rafting

“…High abundances of invertebrates are found on those flats, including species living at the surface of the sediment (epifauna), building burrows in the sediment (infauna), or living in interstitial spaces (meiofauna) (Lenihan and Micheli 2001). Many of these species lack a larval stage and only disperse through temporary drifting in the water column (Armonies 1994, Cummings et al 1995, Giere 2009, Drolet et al 2012, or through sediment resuspension (Commito et al 1995, Jennings andHunt 2009). Winters in temperate intertidal soft-sediment systems are characterized by cold and fluctuating temperatures, which can result in high mortality rates (Armonies et al 2001).…”