Marine vegetation inventories

To make maps of the marine environment, the plants, and connected nature values, one of the basic pieces of information you need is marine biological data.  Not only can this data be used for making models and maps, it also tells us a lot about the underwater landscape and provides knowledge about the existence of species, how common they are, and where you may find them. For three summers during the SEAmBOTH project, field teams in Sweden and Finland collected numerous amounts of data about the plants and animals in the northern Bothnian Bay. Want to know what we found and how we found it?  Scroll down and you will find our results below!

Marine biological data was collected using different methods. For collecting data on macrophytes (underwater plants) we used methods such as drop-video, wading, and scuba diving.

The common thing with these methods is that they give you information about the number of species and the extent of each species (percentage of cover for plants, for example) at the investigated point, the so-called data point. This data point has a defined area, for example 4 m2. At that point you often also collect additional information about the surrounding conditions, for example the type of bottom, the depth, the temperature, the salinity, and the visibility of the water.

During the project we collected information on macrophytes from a total of 23 661 data points located all around the northern Bothnian Bay.

Cumulative accumulation of biological sampling points per year in Finland and Sweden. The red arrow indicates the start of SEAmBOTH project.

In the graph above you can see that the amount of data collected on the Finnish side was substantially larger than on the Swedish side even before the start of the project. In Sweden, the SEAmBOTH project formed the first ever large-scale inventory over the marine area of northern Bothnian Bay.

In total, 167 species of underwater plants were found. Even though over a hundred underwater plant species were found, there were some species that were more common than others. The collected data shows the following top-five for most common species, which together quite well illustrate the plant life of the northern Bothnian Bay:

Filamentous algae on rock under water
1. Unidentified attached filamentous algae. The green “fluff” or “slime” that you come across almost everywhere. If you take a sample of this green stuff and look at it in a microscope, it’s most likely a mixture of real filamentous algae, Cladophora fracta or C. glomerata, a tiny grass-like algae Aegagrophila linnaei, and lots of diatoms covering everything. (Photo by: Metsähallitus)
Perfoliate pondweed, a plant on sandy bottom under water

2. Perfoliate pondweed/ahvenvita/ålnate (Potamogeton perfoliatus). Definitely one of our most common and versatile species. Can be seen almost in any type of habitat. (Photo by: Metsähallitus)
Needle spikerush, small "grassline" meadow under water
3. Needle spikerush/hapsiluikka/nålsäv (Eleocharis acicularis). This species often forms a “lawn” on the very shallow shores of the Bothnian Bay. (Photo by: County Administrative Board of Norrbotten)
Stoneworts, small bushlike plant underwater on sandy bottom
4. Chara-Nitella. The group name for species of charophytes from the genera of Chara and Nitella. Especially if seen in drop-video they may be difficult to differentiate, hence the joint name. (Photo by: County Administrative Board of Norrbotten)
Rough stonewort, plants on sandy bottom underwater
5. Rough stonewort/ mukulanäkinparta/borststräfse (Chara aspera). The most commonly occurring species of the charophytes. (Photo by: County Administrative Board of Norrbotten)

In total, 167 species of underwater plants were found. The findings of type of plant per country is summarized in the table below.

FINSWETotal
Charophytes (species)101010
Water mosses (species)201723
Water mosses (genera)12914
Algae (species)151016
Algae (genera)282032
Vascular plants (species)114113118
Vascular plants (genera)767476
Species159150167
Genera126113132

Table show number of flora species and genera found in the SEAmBOTH area according to field data and literature.

Overall the species, and number of species, found in Sweden and Finland are relatively similar. The main differences in number of species can be found amongst the water mosses and algae. This may be due to slightly different environmental conditions. In Finland the shores are longer and shallower and the water is slightly saltier than in Sweden. It may also be due to the simple reason that almost four times more data points have been collected in Finland than in Sweden. As they say: the more you search the more you’ll find.

The number of vascular plants species were almost identical between the two countries. Three species appeared only in Finland (or has not been found in the marine environment on the Swedish side yet); Hippuris tetraphylla (four-leaf mare’s tale), Stratoites aloides (Water soldier) and Hydrocharis morsus-ranae (Common frogbit). One species was only found on the Swedish side of the Bothnian Bay and that was the invasive alien species Elodea nuttallii (Nuttall’s waterweed). For more interesting information, check out the blog about the similarities and differences of species of the Swedish and Finnish side of the bay.

The water mosses are rather special to the northern Bothnian Bay. Normally such species are mainly found in lakes and streams but here they appear in the sea due to the low salinity of the sea water. In total 23 species have been identified from the area and that may not be the final number. After 12 years of intensive inventories of the marine area on the Finnish side, six new species of water mosses were found in the year of 2019.  In Sweden, a limited number of water moss species were known of in the area before the start of the project.

Water moss on rock
Fissidens fontanus, used to be classified as near threatened (NT) in Finland but now it’s in the category least concern (LC), largely thanks to inventory efforts in the area in recent years. (Photo by: Metsähallitus)
Large watermoss under water
Fontinalis antipyretica, by far the largest of the water mosses in the Bothnian Bay. (Photo by: Metsähallitus)
Water moss and measuring tape under water
Used to be known as Rhyncostegium riparioides, then Platyhypnidium riparioides and nowadays Oxyrrhyncium speciosum in Finland. Apparently, in Sweden it was known all along as Oxyrrhincium. (Photo by: Metsähallitus)

Apart from collecting data on underwater plants, we also did some new findings of animals within the northern Bothnian Bay. On the Finnish side a round goby (Neogobius melanostomus) was observed outside of Oulu, which is the first time it has been seen that far north along the coast. The round goby is an alien species in the Baltic Sea and has mostly been seen in the southern parts, not as far north as in the SEAmBOTH area before. So this is not such a good piece of news.

It was also during a SEAmBOTH field trip that the first individual of the leaf beetle species Macroplea pubipennis was found in Sweden. It had never before been observed within Sweden but was known for existing on the opposite side of the Bothnian Bay around Oulu. Read more about the finding of the beetle and how you search for it.

Written by: Linnea Bergdahl, County Administrative Board of Norrbotten

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