Mapping and assessing Eelgrass (Zostera marina) distribution and growth parameters in two Ramsar-sites

Abstract

Eelgrass (Zostera marina) is a keystone species in coastal ecosystems that provides several crucial ecosystem services such as, habitat formation, carbon sequestration, and coastal protection. This thesis aims to map and assess the distribution of eelgrass and the performance parameters, eelgrass coverage, epiphyte coverage, and shoot height at two Ramsar sites: Sørkjosleira, and Kobbevågen in Balsfjord, Troms, Norway. A Blueye ROV was used to do the mapping. Additionally, this thesis aims to investigate if the eelgrass meadow at Sørkjosleira is negatively impacted by Tine dairy plant, by measuring nutrient concentrations. And to investigate if the eelgrass depth limit at Sørkjosleira is affected by the sediment grain size. Results showed a reduction of eelgrass area at Sørkjosleira of 28.7% since 2009. At Kobbevågen there was a 2.8-fold increase in eelgrass area. Nutrient levels were higher at Sørkjosleira. This may be caused by comparatively more agriculture in the vicinity than at Kobbevågen. Eelgrass coverage and shoot height were lower at Sørkjosleira, but epiphyte coverage was higher compared to Kobbevågen. Grain size was similar above and below the depth limit of eelgrass, indicating that the depth limit is not affected by the physical substrate composition. The higher nutrient levels at Sørkjosleira may negatively affect eelgrass health.