Rapport no 166 : Kartering av undervattensvegetationen i Fladan och Estviken, Åland
Liljedahl, Annika (2023)
Åbo Akademi, Husö biologiska station
2023
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe20231023141050
https://urn.fi/URN:NBN:fi-fe20231023141050
Tiivistelmä
As a request from the government of Åland, vegetation mapping of macrophytes in two shallow bays on Åland was carried out during the summer of 2023. These bays, Fladan and Estviken, south of Sund, had not previously been mapped. The purpose of this study was to, based on the composition of macrophytes, assess and study the distribution of shallow vegetated soft bottoms and their status in Sund. The mapping of the sea bays was carried out by echo sounding. The sonar transects were placed parallel to each other at 50-meter intervals and ran in straight lines across the bays from one edge of the bay to the other. Through this, data on the vegetation coverage could be collected. The Visual Habitat software was then used to analyze the collected data from the echo sounding, and maps of the vegetation cover could be produced. Drop video was used to investigate which macrophytes were growing in the bays, and also where they were growing. Drop video was done at predetermined points in the bays with at least 50 m in between each point. Raking of the sea bottoms was used as a complementary method for identifying plants.
The result from the echo sounding showed that the highest concentration of underwater vegetation could be found in the inner parts of the bays and along the shorelines in both Fladan and Estviken. A total of eight species were identified in Fladan and six in Estviken. The highest concentration of underwater vegetation was found in the northern parts of the bays. The inner parts also showed the highest species diversity. Myriophyllum sibiricum, Stuckenia pectinata, Ceratophyllum demersum and Potamogeton perfoliatus were the most common species found. Of the 15 species I expected to find, nine were found.
Fladan and Estviken are geographically located next to each other and therefore they contain largely the same species. The reason why the bays, especially Estviken, contained so few and sparsely placed species was probably due to the fact that they are both relatively exposed and therefore receive more wind and wave movements than more protected bays. There is however a possibility that a red-listed species, Convergent stonewort Chara connivens, grows in Estviken. The possible occurrence of this species should be investigated more thoroughly in future follow-up studies.
The result from the echo sounding showed that the highest concentration of underwater vegetation could be found in the inner parts of the bays and along the shorelines in both Fladan and Estviken. A total of eight species were identified in Fladan and six in Estviken. The highest concentration of underwater vegetation was found in the northern parts of the bays. The inner parts also showed the highest species diversity. Myriophyllum sibiricum, Stuckenia pectinata, Ceratophyllum demersum and Potamogeton perfoliatus were the most common species found. Of the 15 species I expected to find, nine were found.
Fladan and Estviken are geographically located next to each other and therefore they contain largely the same species. The reason why the bays, especially Estviken, contained so few and sparsely placed species was probably due to the fact that they are both relatively exposed and therefore receive more wind and wave movements than more protected bays. There is however a possibility that a red-listed species, Convergent stonewort Chara connivens, grows in Estviken. The possible occurrence of this species should be investigated more thoroughly in future follow-up studies.