Rapport no 167 : Vegetationskartering av Mönsfladan och Onsviken - ett återbesök
Ikonen, Anna (2024)
Ikonen, Anna
Editori
Cederberg, Tony
Åbo Akademi, Husö biologiska station
2024
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe202401234007
https://urn.fi/URN:NBN:fi-fe202401234007
Tiivistelmä
A vegetation mapping of Mönsfladan and Onsviken was carried out in summer and autumn of 2023. This as a request from the Government of Åland and Åbo Akademi University. Mönsfladan is a 1,5 km long shallow bay in the northern part of Geta and it was last mapped in 2013. Onsviken is an 800 m long shallow bay in the northern part of Saltvik and it was last mapped in 2005 and 2008. The idea with the revisit was to investigate long time changes in shallow bays.
These two shallow bays were selected for different reasons. In Mönsfladan, a plan involving the construction of a canal between Mönsfladan and Engrundsfjärden has surfaced again. Therefore the Government of Åland wanted to map the vegetation Mönsfladan in order to get a more updated picture of the ecological state of the area. Onsviken again had been seen as an important charophyte bay and was said to be worth protecting, and the Government of Åland wanted to know if the situation still is the same.
The mapping was done by snorkelling along a transect line and diving down to the bottom every 10 meters. The species in a 50 x 50 cm square were identified and the coverages estimated. The results were then compared with the earlier mappings.
Mönsfladan had not changed so much since the last mapping and the red listed Chara horrida could still be found there. This alters the plan to make the canal. Chara horrida is red listed, critically endangered and protected by law on Åland and for this reason C. horrida or its habitat are not allowed to be disturbed, which likely rules out dredging. Onsviken had changed a lot since the last mapping. The dominating species in 2005 and 2008 had been charophytes like Chara aspera and Chara tomentosa but in the mapping 2023 the dominating species were Stuckenia pectinata and Myriphyllum spicatum. The fact that the overall coverages of charophytes had decreased rapidly in Onsviken, since the last mapping, indicates that the ecological status of the flada has decreased.
These two shallow bays were selected for different reasons. In Mönsfladan, a plan involving the construction of a canal between Mönsfladan and Engrundsfjärden has surfaced again. Therefore the Government of Åland wanted to map the vegetation Mönsfladan in order to get a more updated picture of the ecological state of the area. Onsviken again had been seen as an important charophyte bay and was said to be worth protecting, and the Government of Åland wanted to know if the situation still is the same.
The mapping was done by snorkelling along a transect line and diving down to the bottom every 10 meters. The species in a 50 x 50 cm square were identified and the coverages estimated. The results were then compared with the earlier mappings.
Mönsfladan had not changed so much since the last mapping and the red listed Chara horrida could still be found there. This alters the plan to make the canal. Chara horrida is red listed, critically endangered and protected by law on Åland and for this reason C. horrida or its habitat are not allowed to be disturbed, which likely rules out dredging. Onsviken had changed a lot since the last mapping. The dominating species in 2005 and 2008 had been charophytes like Chara aspera and Chara tomentosa but in the mapping 2023 the dominating species were Stuckenia pectinata and Myriphyllum spicatum. The fact that the overall coverages of charophytes had decreased rapidly in Onsviken, since the last mapping, indicates that the ecological status of the flada has decreased.