Mapping of eelgrass (Zostera marina) using updated methodology in Innherred intermunicipal cooperation

Summary

It is important that managers and planners have knowledge of the areas of importance for biodiversity. Innherred intermunicipal cooperation therefore wanted an updated status of known eelgrass (Zostera marina) meadows and a mapping of previously unknown meadows. The eelgrass meadows were mapped 11-14. July 2016 using water binoculars in the shallow areas and an underwater camera from a boat in the deeper areas. Field mapping, delineation of eelgrass meadows and valuation was conducted according to the standard of the National program for mapping biodiversity – coast. Of the 27 eelgrass meadows, two had A (national) value, one had B(regional) value and 24 had C (local) value. The total area for all meadows was 581 742 m2. The largest meadow was 202 395 m2, the smallest one only 740 m2. The deepest observed point of seagrass growth (regardless of density, height or patchiness) varied between 0.3 and 3.1 m between meadows (standardized to the lowest astronomical tide level). If we compare the eelgrass meadows mapped now (2016) with what was mapped for the same area in 2009/2010, there were a few changes, some meadows had decreased in size, other had become more fragmented. Lower growth limit has not changed since 2009/2010. The same is the case for the proportion of the points consisting of dense or moderately dense eelgrass.