Seed to meadow - developing intertidal seagrass restoration

Abstract

In coastal waters around the globe, seagrasses form the basis of productive ecosystems. Unfortunately, these valuable ecosystems have suffered massive losses during the last century and are in dire need of effective conservation measures. In this thesis, we investigated if and how eelgrass (Zostera marina) can be restored in the intertidal Wadden Sea. Through an applied and adaptive approach we were able to develop and optimize a new restoration method (DIS-method), with which seagrass seeds are injected into the sediment with normal caulking guns. By sowing seagrass with the DIS-method in spatial designs that trigger beneficial intraspecific feedbacks we were able to restore very high seagrass densities (~60 plants/m²) with high efficiency. Our restoration efforts not only resulted in seagrass establishment, but also quickly increased the diversity of benthic animals to levels found in natural seagrass meadows. Additionally, we found that benthic animals can offer previously untapped information about seagrass habitat suitability, a discovery that can potentially help with the identification of suitable restoration sites. Our results show that seagrass restoration is not only possible in the intertidal Wadden Sea, but can in fact even be highly successful and effective. This is highlighted by the fact that our restoration efforts led to the establishment of the largest seagrass population in the Dutch Wadden Sea (1 million plants scattered over 650 hectares). In conclusion, the applied knowledge we have gathered can in the future be used to effectively restore these important plants and their associated ecosystems in coastal areas worldwide.