The northern Bothnian Bay is shared by Finland and Sweden, and in many ways the sea is the same. In other ways, differences occur in underwater nature between both sides of the border, although this border only is a human concept and does not affect marine life. One thing that has puzzled our colleagues on the Finnish side is our stories about this mystical charophyte, Chara braunii, that we have often seen in the waters on the Swedish side of the SEAmBOTH area. Sometimes it grows so densely that it forms lush green meadows in our shallow bays. However, on the Finnish side, this species has not been encountered in SEAmBOTH investigations, all until last summer.
Chara braunii is a charophyte, which is a green algae that resembles a plant. Charophytes attach to soft bottoms in fresh and brackish waters often forming charophyte meadows. Chara meadows are a valuable but declining nature type, as these algae commonly are susceptible to eutrophication. Chara braunii is a special charophyte species because, from a national perspective, it is very uncommon and defined as vulnerable (VU) in the red list of threatened species in both Finland and in Sweden. In Sweden, it is currently known to exist only in the northern Bothnian bay. In Finland it has previously been found in a total of 15 sites in the whole country: in the Bothnian Bay and a few freshwater sites in Southern Finland.
This species is quite easy to recognize, as far as charophytes go. Unlike other species of Chara, it has no bark cells (cortex), which means that its branches are formed of single elongated transparent cells. From other cortex-less genera (eg. Nitella and Tolypella), it can be differentiated by its unbranched branchlets and the presence of spines. Once seen, it is easy to recognize just by a glance, as it is amazingly attractive, with its bright green color, regular build and striking and numerous reproductive organs.
So Chara braunii has become very familiar to us marine biologists on the Swedish side of the SEAmBOTH-area. It prefers sheltered bays in and around estuaries, and since we have studied a lot of sheltered bays this last year, our number of observation sites has also grown. Most of these places have never been mapped before, so this species has shown itself to be a lot more common in this area than thought before. In the meantime, many years of underwater mapping went by on the Finnish side before the first sample was found. Then, we hit the jackpot on the islands in the Kemi River estuary. Just last year, the observation sites doubled in Finland. Still these observations include only occasional individuals, not larger occurrences. Perhaps this is due to the straighter shoreline in Finland, as the species prefers sheltered sites that are more numerous on the western side of the border. Either way, we are happy for every new finding of this pretty but vulnerable charophyte.
Written by Petra Pohjola, County Administrative Board of Norrbotten