Rapport nr 165: Vattenvegetationen i grunda havsvikar, ett återbesök till havsvikar karterade 2002

Abstract

During the summer and autumn of 2022, a vegetation mapping of 12 shallow bays around the Åland Islands was carried out as a request from the government of Åland and Åbo Akademi University. Most of the shallow bays had not been investigated since 2002. This vegetation mapping was a revisit to these areas to be able to investigate what had happened in 20 years. Some of these shallow bays are eutrophicated and others are not. The eutrophication level might also have changed in 20 years. Some species dominate eutrophicated areas and they can outcompete the less adaptable species. When the nutrient concentration increases the species that can fastest absorb and use these nutrients are favored. When investigating the water vegetation in shallow bays, there are some species that clearly indicate a healthy bay and others that indicate a bay in a bad shape. Charophytes, like Chara tomentosa, C. baltica and many others, are common species in non-eutrophicated and clear water. Filamentous algae and Myriophyllum sp. are common in eutrophicated areas. The mapping was done by diving to the bottom along a marked transect every 10 meters of the transect. The species found inside a 50 cm x 50 cm square were identified and the coverage of the different species was estimated. When comparing the data from the 2002 mapping with the 2022 mapping the state of most of the shallow bays have gotten worse. The coverage rate of charophytes in most of the shallow bays has decreased drastically since 2002. Instead, the coverage of for example Stuckenia pectinata has increased.