Eelgrass meadows have disappeared from many areas of Skagerrak and Kattegat since the 1980s. This is the conclusion of a new study conducted by researchers at the University of Gothenburg on behalf of the Swedish Agency for Marine and Water Management.
The study shows that extensive losses of eelgrass have occurred in Skagerrak and Kattegat since the 1980s. The total area of eelgrass meadows studied has decreased by approximately 45 per cent (corresponding to 1,377 hectares) compared to the current distribution.
Using drones
Researchers from the University of Gothenburg have studied changes in the areal extent of eelgrass using, among other things, flying drones. They have compared data from three time periods: the 1980s, 2000s and 2020s in Västra Götaland County and in Kungsbackafjorden. In total, 224 bays were surveyed.
"During the 1980s, many municipalities conducted detailed inventories of the vegetation on shallow soft bottoms in the area. This constitutes a unique material in Sweden that enables a historical comparison of the distribution of eelgrass," says Per-Olav Moksnes, professor of marine ecology at the University of Gothenburg, who led the study.
Some positive factors
The loss of eelgrass exceeded 20 per cent in all coastal water types surveyed, both in the 2000s and in the 2020s. However, these losses were not evenly distributed across the area, but mainly occurred in the northern and southern parts of Bohuslän, and in Kungsbackafjorden. In other areas, only minor losses have occurred. However, some positive factors can be noted, according to Per-Olav Moksnes.
"The greatest losses occurred between the 1980s and 2000s. Since then, the situation has stabilised and the distribution of eelgrass has begun to increase in most areas, although it is still a long way from the distribution of the 1980s. However, in the area around Hakefjorden and Sälfjorden in southern Bohuslän and at Sydkoster, extensive losses have continued since the 2000s," he says.
Measures to save eelgrass
The loss of eelgrass have mainly occurred in the shallowest parts of the meadows (0-3 metres deep) in medium-protected bay areas.
"We believe that suffocating algal mats, which have increased due to eutrophication and overfishing, as well as other factors that affect shallow-living eelgrass, are behind the sharp decline, says Elisabeth Anderberg, investigator at the Swedish Agency for Marine and Water Management.
To save the eelgrass, future important measures could be increased area protection, replanting of eelgrass, and improved knowledge base and methods for assessing condition and status.
"It could also be important to prohibit certain harmful activities in, or near, eelgrass meadows when licence assessments are made," says Elisabeth Anderberg.
