Investigation of the local and spatial roughness effects of oyster reefs and blue mussel beds

The German Wadden Sea has undergone significant changes in the last years due to the invasion of the pacific oyster (Crassostrea gigas). Spreading from aquaculture farms, C. gigas has extended its spatial coverage throughout the German Bay most likely due to increased water temperatures as a result of climate change. Juvenile oysters require hard substrates to settle, which they found on blue mussel beds on the intertidal flats. As a result, pacific oysters have replaced the formerly typical blue mussel beds as the pristine and predominant biogenic habitat. In contrast to the loose connections between the individual blue mussels, C. gigas form extremely strong bonds resulting in complex, rigid surface structures also referred to as oyster reefs.

Oyster reefs are highly resistant to mechanical stress including hydrodynamic loadings. Hence, it is hypothesized that the rough, rigid reef surfaces dampen waves and tidal currents due to frictional dissipation and can significantly reduce the wave energy reach-ing a shore. To date, very little research has been conducted on the inter-relation between oyster reefs and adjacent hydrodynamics. The overarching aim of the BIVA-WATT project is hence to understand the underlying processes involved and quantify the en-ergy dissipation caused by oyster reefs.