MEPS 431:255-265 (2011)  -  DOI: https://doi.org/10.3354/meps09121

ABSTRACT: Spatial structuring in species distribution can be caused by effects of biotic or abiotic factors on the vital rates (survival, growth or reproduction) or movement of individuals. Here, we studied the distribution patterns of a dominant infaunal invertebrate, the amphipod Corophium volutator, on an intertidal mudflat and evaluated the relative contribution of vital rates and movement on the formation of intermediate-scale patterns (10 to 100 m). We found a clumped distribution at scales ranging from 0.2 to 100 m and occasionally the presence of large-scale gradients. At intermediate scales, variation in density in the mud associated better with variation in movement variables (density of swimmers and immigration) than demographic variables. Predictions from local population models not including migration often largely underestimated increases in local density, leaving immigration as the only mechanism explaining variation in density. Amphipod swimming was directed, and the direction of swimming corresponded to overall density gradients observed on the mudflat. We concluded that movement of C. volutator is an important process causing and maintaining intermediate-scale distribution patterns. Spatial variability in supply of individuals, likely linked to timing of swimming coupled with hydrodynamic conditions, translates into notable variation in population density distributions.

KEY WORDS: Spatial patterns · Soft sediment · Dispersal · Immigration · Corophium volutator