Marstrand, located in the southern Bohuslän Archipelago, is situated in the northeastern part of the Kattegat, on Sweden’s west coast. The Kattegat and the neighboring Skagerrak form the transitional area between the salty North Sea and the brackish Baltic Sea. The Kattegat is fairly shallow with a mean depth of only 23 meters, but its deeper areas, including the Kattegat and Djupa Rännan trenches can reach more than 150 meters. The latter is connected to the former, which runs 45 km south through mainly Danish waters.
The deeper parts of the Kattegat, including the aforementioned trenches, boast muddy soft bottoms, and communities, like sea pens with burrowing megafauna, that are specialized to live in the particular physical conditions of the area. In shallower waters, the substrate is more diverse and includes bottoms with various stone covers and sand. Different benthic communities also reside there, including octocoral gardens. In the even shallower photic zone, macroalgae and eelgrass meadows occur.
Oceana conducted underwater studies with an underwater robot (ROV) and scuba divers in the area 2011, 2012 and 2013. We documented several communities, including sea pen community, eelgrass meadows, sponge aggregations (Suberites virgultosus), and coral gardens. We also documented bottom trawling tracks on a mud bottom that is located inside this proposed area.
The local authorities (Länsstyrelsen Västra Götaland) are in the process of protecting a coastal area around the island Marstrand. Oceana have provided the authorities with footage from the area, as well as inputs for the hearing process in early 2014. Swedish Green party is supporting protection of larger area, covering also deeper parts as Oceana has proposed.
