Spatial pattern in the amphipod Corophium volutator in the Ythan estuary
Understanding patterns of heterogeneity and their underlying processes at a variety of scales is the basis of ecology. Heterogeneity in the distribution of the amphipod Corophium volutator was assessed at large (10's to 1000's of m), intermediate (m) and small (cm) scales on the Ythan estuary, where it occurs in abundance, and the role of abiotic features, interspecific interactions and intraspecific interactions and individual behaviour in the maintenance and formation of this heterogeneity investigated. Patchiness at small spatial scales of the order of 0-6 cm was demonstrated in situ in winter and summer populations and under laboratory conditions. The processes underlying this heterogeneity seemed to be related to intraspecific interactions and individual behaviour rather than to interactions with either abiotic features or with other infauna. Conversely, heterogeneity at large and intermediate scales seemed related to patchiness in other biotic features (e.g. macroalgal mats) and a complex of related abiotic features (e.g. topography, sediment grade, inundation period and hydrography) rather than interactions with other infauna or megafaunal predators. Studies on the swimming and crawling mobility of Corophium, suggested data adult males dominate crawling activity, but that this only represents on average 3% of the total population in the sediment. Swimming activity is similarly generally low and dominated by adult males, but periodic peaks occur on night high tides in the neap to spring progression with swimming dominated by juveniles. The relative immobility of adults is likely to maintain heterogeneity at large and intermediate scales within time scales of the same order of magnitude as their life-time, but over longer time-scales heterogeneity at these scales may change with changes in biotic and abiotic features, recruitment and survival of juveniles. Conversely small-scale heterogeneity seems likely to change constantly in position in space through time, although its form may be maintained by intraspecific interactions.