Due to a fungus (seaweed disease) and the consequences of the construction of the Afsluitdijk, seagrass has disappeared. Currently, there are no signs of the presence of perennial submerged large seagrass in the international Wadden Sea. The Waddenmozaïek project has investigated what complicates the restoration of submerged large seagrass. Together with the University of Groningen, we are now going to investigate how these bottlenecks can be resolved.

Bottlenecks

In the recently completed research it was examined where suitable locations are to restore submerged large seagrass and what bottlenecks hinder that. Examples of bottlenecks include wave action and the amount of available light. The new research focuses on further developing knowledge about these bottlenecks and their effect on submerged large seagrass. Furthermore, the research also compares seagrass plants from other Western European countries on plant properties, such as leaf strength and leaf flexibility. The goal is to map possible suitable donor locations. Subsequently, it will be investigated whether there are methods to sufficiently resolve the bottlenecks to start field trials in the Wadden Sea. On behalf of Rijkswaterstaat, marine biologist and PhD student Raven Cammenga, together with a team from the University of Groningen, will conduct the research.

Importance of Seagrass

Seagrass beds are fundamental to a healthy underwater ecosystem. The aquatic plant forms large fields, where water flows more slowly, and sand and silt settle to the bottom. This results in clearer water. The network of seagrass roots stabilizes the seabed. This provides natural reinforcement and elevation of the bottom. As waves lose part of their strength and hit the coast less hard, coastal erosion is countered. Moreover, the plant stores CO₂, making seagrass play an important role in the fight against climate change. According to scientists, seagrass beds are much more efficient in carbon storage than most forests.

Seagrass beds are also of great importance for biodiversity. They serve as nurseries for fish. They also provide perfect habitats and shelter for small animals like shrimp, herring, and seahorses. These can in turn serve as food for birds and fish. Thus, seagrass beds form an important link in the food chain, both underwater and above water.

The seagrass restoration focuses on both submerged large seagrass and intertidal large seagrass. Seagrass restoration in the Wadden Sea was for a long time a project under the guidance of Natuurmonumenten. Due to responsibilities from the European Water Framework Directive and Natura 2000, we took over the project after a bridging year starting in 2022. We are collaborating with several organizations on a multi-year approach to permanently restore seagrass in the Wadden Sea. This is done through restoration, monitoring, and research. Since the takeover, a lot of knowledge has been gained about intertidal large seagrass (Zostera marina). In recent years, this seagrass has developed well, especially south of Ameland and on Griend, but the trial fields with seagrass still need to be further expanded.

Differences Between Submerged and Intertidal Large Seagrass

Although intertidal and submerged large seagrass are both of the same species (large seagrass), the plants also differ. Intertidal large seagrass is a 1-year plant that reproduces via seeds. The plant has a flexible stem that lies against the seabed at low tide, preventing drying out. Submerged large seagrass is a perennial plant that mainly reproduces by new plants arising from parts of an existing plant. It has a sturdier stem that is more resistant to currents and wave action. Due to these differences, restoration measures that are effective for intertidal large seagrass cannot be directly applied to submerged large seagrass.