We have it, you don’t

The nature in the northern Bothnian Bay in the SEAmBOTH area is in many ways similar on the Swedish and on the Finnish side. Sure, the Finnish side is more flat and the shores do not slope as fast as on the Swedish side, but both have large river estuaries, many lagoons and bays, with some islands too.

Yet, there are some differences between the species that can be found in the neighboring countries. Hippuris tetraphylla can be found in large numbers in Krunnit archipelago on the Finnish side. It only exists in some areas far away from the SEAmBOTH area in Sweden. It is possible that the right kind of habitat, mudflats and coastal meadows that are sometimes covered by water, sometimes not, can only be found in abundance in Finland. Or is it just a matter of finding it in Sweden as well?

Hippuris tetraphylla – a common sight in the Krunnit archipelago but a rarity in Sweden. (Photo by Alejandra Parra, Metsähallitus)

An alien species, Elodea canadensis, is found in both countries, but it’s cousin, equally aggressively spreading Elodea nuttallii, can only be found in Sweden, and only a few kilometers from the border. Again, it’s probably just a matter of time when it arrives in Finland, but so far that hasn’t happened.

There are some differences between the number of water mosses found in Finland and Sweden. The species list for the area in Finland is a lot longer, but this does not necessarily reflect the reality in nature. Oulu University happens to have one of the leading authors of mosses in Finland, and it’s easy for the Finnish team to take all suspicious water mosses to be properly identified. Three species, Fissidens adianthoides, osmundoides and pusillus look exactly the same underwater and also with our field microscope. They can only be identified with a proper microscope that can be found at the University. If the Swedish colleagues don’t have the same handy access to a water moss expert, differentiating with all the dozen or so species of them becomes much trickier.

In the field it is impossible to diffrentiate the water moss Fissidens osmundoides from its relatives. To make sure what species it is, it must be taken to lab and identified under microscope. (Photo by Essi Keskinen, Metsähallitus)

One Chara species is still a mystery. Chara braunii occurs as lush meadows in Sweden and as lonely individuals in Finland. And we just started finding it on the Finnish side as well. For some reason, it never occurred in our previous mapping areas before, and it’s not an identification error either, because the species is very easy to distinguish, even with a naked eye. Another question mark is Chara baltica. Old reference books say it can be found in Sweden, all the way to the border, and then it abruptly stops and can’t be found in Finland at all. In recent years though there have only been the odd sighting of it on within the SEAmBOTH area on the Swedish side. So questions arise: Has the distribution of the species changed over the years or has species identification changed?

Quite often it’s also a matter of finding something if you know where to look for it. The small beetle, Macroplea pubipennis, had never been found in Sweden before. Petra, who has been successfully looking for them in Finland, joined the team in Sweden last year and soon enough she started finding them in Sweden and in the SEAmBOTH area as well.

You need to know what to look for to be able to find the aquatic beetle Macroplea pubipennis (Photo by Petra Pohjola, County Administrative Board of Norrbotten)

One thing is for sure – the more data we collect from both sides of the border, the more common ground we find. Some differences will remain, but mostly they seem to be just artefacts caused by more mapping effort put into the Finnish side. This is exactly why we need cross-border projects like SEAmBOTH.

Written by Essi Keskinen, Metsähallitus

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