Validating GIS tool to assess eelgrass potential recovery in the Limfjorden (Denmark)

Eelgrass is a key indicator for the water quality in Europe (WFD, European Union, 2000). However, although water quality has been improved in most Danish water bodies, the eelgrass population does not seem to be recovering. In this study, we validate and further develop a GIS tool designed by Flindt et al. (2016), to evaluate the potential of eelgrass reestablishment in Danish waters. The GIS tool was tested in two large broads of the Limfjorden, Løgstør and Lovns broad (Denmark), where two scenarios are run. The first scenario was set up including modelled data, whereas the second scenario included both monitored and modelled data. All scenarios were validated with monitored data collected over a 5 years period in the two broads. The developed GIS tool highlights areas with eelgrass potential, both for vegetative growth and sexual reproduction, in accordance with those found in situ in the period 2009–2013, in the two investigated broads. A combination of modelled and monitored data was found to be optimal to achieve accurate predictions for eelgrass development in the Limfjorden using this GIS tool. In order to implement the current model or to use this GIS tool in other locations, it is needed to have detailed knowledge of the area in focus, especially on the controlling ecosystem parameters and pressures. This eelgrass GIS tool is been proven to be especially beneficial as site selection tool for marine spatial planning e.g. in relation to the implementation of the WFD and the ICZM directives (WFD, ICZM), to help assessing anthropogenic/targeted environmental impacts e.g. assessing mussel fisheries impacts and is as well a powerful tool to optimize monitoring cost efficiency. Finally, the described GIS tool, originally set for Odense fjord (Denmark) by Flindt et al. (2016), has been validated with data from Limfjorden, corroborating the efficiency of the studied tool in Danish waters.