Sterre Witte

“A solid basis for shellfish reefs as a biodiversity hotspot”

Mussels and oysters build reefs in which they live in high densities. They are ecosystem engineers: their reefs form a good basis for other species to attach to and serve as shelters from harsh conditions. They are a nursery for fish and an important food source for birds, fish, crabs and shrimp. By creating optimal circumstances that other species can benefit from, shellfish reefs are biodiversity hotspots. In order to get a better understanding of the functioning of shellfish reefs, I compare their biodiversity and food-web structure with the bare seafloor areas around them.

Providing a foothold

In the past, there used to be many shellfish reefs in the Wadden Sea, but their occurrence has declined severely. The goal of my research is to find opportunities for restoring these lost subtidal shellfish reefs. Forming a shellfish reef from scratch on a barren seafloor is difficult, the reef itself needs something to hold on to. One way to assist mussel and oyster reefs, is to offer them a suitable material to settle on; a substrate. During my PhD project I am studying which properties make a substrate surface attractive for shellfish settlement.

A complex basis

One important substrate property is the complexity of the surface. Imagine a flat sheet of paper with its smooth, non-complex surface. If you crumple that same sheet of paper into a ball, it will have a more complex surface with folds and crevices. Likewise, a flat surface does not offer a reliable shelter, whereas a crumpled substrate with folds and crevices offers young mussels and oysters a secure basis. This gives them a space to hide from high flow velocities and predation. Promoting substrate complexity could therefore increase the settlement success and contribute to the long-term stability of subtidal shellfish reefs and their associated ecosystem functions.