MEPS prepress abstract  -  DOI:

Response of intertidal benthic macrofauna to migrating megaripples and hydrodynamics

Daphne van der Wal*, Tom Ysebaert, Peter M. J. Herman


ABSTRACT: Migrating flow-transverse meso-scale intertidal bedforms (megaripples or dunes) may pose disturbance, but may also provide heterogeneity in micro-habitats to the inhabiting fauna. We investigated how the macrofauna community responds to these migrating intertidal bedforms, based on surveys in the Westerschelde estuary. Considering the entire estuary, low and high energetic intertidal areas differed in macrofauna, and high energetic flat areas had a macrofauna community intermediate to those in low energetic flat areas and high energetic areas with megaripples. In megaripple areas on a polyhaline and a mesohaline tidal flat, the macrofauna community depended on hydrodynamics, morphodynamics, grain-size, elevation and steepness of the megaripples. The relative importance of the environmental variables for structuring the macrofauna community differed for each site. Within the megaripples, conditions on crests, flanks and in troughs were distinctly different: crests had more chlorophyll a and coarser sediment, and troughs had higher carbon and mud contents. The micro-habitats supported a different macrofauna community, but with a very large overlap in species. Troughs typically had higher species richness, while crests had higher densities of particularly (mobile) surface deposit feeders. Part of the macrofauna could benefit from the habitat heterogeneity within the megaripples, but the effect was relatively small. The distribution of macrofauna in the intertidal zone was particularly regulated by overall current velocities and bedform morphodynamics.