Spatial variability in recolonisation potential: influence of organism behaviour and hydrodynamics on the distribution of macrofaunal colonists

Estuaries are dynamic environments in which human and natural disturbances can result in clearing or smothering of soft-sediment communities. Hydrodynamic models simulating organism transport predict that recovery potential of benthic communities will be affected by: (1) location within an estuary, (2) proximity to the source of colonists and (3) the relative buoyancy and life-history strategies of colonists. To test these predictions, we deployed sediment traps daily at 7 locations for 7 d across a range of habitat types within a tidally dominated estuary, to estimate the pool of available colonists. Our results confirmed model predictions in that location strongly influenced the number of trap colonists. In particular, sandflat sites received more trap colonists than tidal creek sites. Most trap colonists were either juvenile or adult life stages. Species collected in traps differed from the benthic communities in the surrounding sandflat in that bivalves were over-represented and polychaetes were under-represented. Most bivalve colonists were collected as post-settlement juveniles, indicating post-settlement dispersal (byssal-thread drifting or bedload transport) as a primary means of transport. Polychaetes with adult swimming stages were collected in the traps, while tube-dwelling polychaetes were rarely collected. Organism transport and sediment deposition were highest during a wind-wave event. This research demonstrates the value of linking biology and hydrodynamic modelling to predict the potential pool of colonists available for recolonisation, and thus determine thresholds in the recovery from disturbance on an estuary-wide scale.