Large-scale transplantation succes of Zostera marina in Danish estuaries through site selection and identification of stressor thresholds

In Denmark, seagrass habitats have undergone a massive decline and less than 10 - 20 % remains today, which is similar to the global decline tendencies of seagrass. This has resulted in a growing interest in restoring seagrass habitats and is in Denmark planned to be implemented as a marine measure to reach a good ecological status in according to the EU Water Frame Directive (WFD). Researchers from the University of Southern Denmark have since 2014 been developing and testing technics to successfully restore eelgrass (Zostera marina). Through identification of stressor thresholds (e.g. nitrogen loading parameters and destructive bioturbation) and careful site-selection three large-scale transplantations (> 5.000 shoots) of Zostera marina have been successfully established. These large-scale transplantation efforts have reached shoot densities similar to those of natural meadows within app. two years. The transplantations were made in the shallow Danish estuaries (one in Horsens Fjord and two in Vejle Fjord) and are one of the few examples of a successful large-scale restoration of seagrass in Europe. This presentation highlights the site-selection process, the identification of stressor thresholds and the temporal development of the successful transplantations.