How we do it: Investigating underwater vegetation

What plants grow at the bottoms of the northern Bothnian Bay? What species can you expect to find, and do they differ depending upon location?

Inventories of the underwater vegetation are crucial in order to increase the knowledge of the marine environment  of the Bothnian Bay. As part of the SEAmBOTH project, inventories were made in the pilot areas of Haparanda and Råneå in september 2017 (see maps below) at in total 13 different locations. To read the full inventory report, click here.

Location of sites around Haparanda (above) and Råneå (below) archipelagos where divers did underwater inventories of vegetation. (Maps by: Sveriges Vattenekologer AB)

When investigating the underwater vegetation, the divers laid a transect (a 100-200 meter long measuring tape) straight out from the shoreline towards sea.  They then swam along the line, recording the type of bottom (soft, sandy, rocky etc) as well as what species of plants were there and the percentage of area each specie covered.  The coast of Norrbotten is very shallow, and swimming along the transect line the divers never reached a depth deeper than six meters.

Diver swimming along a transect line. (Photo by: Anders Wallin, Sveriges Vattenekologer AB)

Species and the percentage of plant cover are some of the things the diver notes and writes down during the inventory. (Photo by: Anders Wallin, Sveriges Vattenekologer AB) 

For birds and many species of fish, shallow bottoms with vegetation are very important. They provide food, shelter and protected places for young fish to grow up in. How much vegetation and to what depth the plants can grow depends for example upon the salinity (salt content of the water), the availability of light at depth, the type of bottom and the exposure to waves.

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