Impact of settlement and early post-settlement events on the spatial distribution of juvenile Mya arenaria on an intertidal shore

Recruitment patterns of marine bivalves are influenced by pre-settlement, settlement and post-settlement factors. Settlement patterns of the soft shell clam, Mya arenaria, were recorded at multiple tidal heights at Mill Cove, New Brunswick. It was found that the initial settlement of M. arenaria occurred at all locations on the shore and was significantly related to adult abundance and sediment grain size. At all transects there was a decrease in abundance of M. arenaria within the first month after settlement, but not all transects showed a similar decrease. While predation likely contributed to the decrease in abundance at all locations on the shore, post-settlement dispersal was an important factor in determining changes in distribution of the juvenile bivalves on the shore. By utilizing bedload traps, spatial variation in the movement of both sediment and M. arenaria was quantified. Transplants of stained clams quantified immigration and emigration rates and showed there was emigration away from the low transects, but no net movement at the high transects on the shore. Dispersal rates of recently settled M. arenaria are generally linked to sediment movement. At Mill Cove, tracking of sediment indicated that the movement of sediment increased from 1-2 m day− 1 in the high intertidal to 5-8 m day− 1 in the low intertidal, and all movement was in a shoreward direction. This study demonstrates that post-settlement dispersal can greatly affect the distribution of juvenile bivalves on an intertidal shore.