BioTide - The role of microbial biodiversity in the functioning of marine tidal flat sediments

At first sight, coastal tidal flats appear to be barren expanses of mud and sand. A closer look however reveals that they are teaming with life. Minute tracks and holes betray the presence of worms, crustaceans and shellfish, which in turn are eaten by fish, migratory birds and humans. In the BIOTide project, we show that this rich diversity of animal life is supported by highly productive biofilms which are dominated by microalgae. At low tide, these biofilms form intense brown patches at the mud surface. Using photosynthesis, the microalgae produce organic carbon which is rapidly taken up in the whole food web. We showed that the biodiversity of these biofilms has a strong impact on their functioning, such as carbon cycling, and that this effect is mediated by sophisticated interactions between different microbial life forms, from bacteria and microalgae to minute roundworms. Tidal environments are also ideal sites for aquaculture, as the biofilms also represent a highly nutritious food source for commercially important animals such as oysters and sea urchins. Studying tidal flats however is not easy, as they are often very inaccessible and sometimes even dangerous. We therefore developed tools which allow documenting the biodiversity and ecosystem functioning of whole tidal flats from the air ('remote sensing'), using drones, planes and even satellites. Taken together, our results show that the healthy functioning of these important coastal systems depends on the biodiversity of the microbial biofilms that inhabit the tidal flats.