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Invasive "moss animal" gains foothold in Finland

The invasive species has made inroads with recent torrid conditions heating up lakes in Finland.

Pectinatella magnifica -sammaleläin
Pectinatella magnifica, also known as Bryozoa or moss animal seen at a beach in Lempäälä in the Tampere region. Image: Marjut Suomi / Yle

Two years ago, residents of Lempääla in the Tampere region noticed an odd jelly-like organism at a local beach.

Now, with recent torrid conditions heating up lakes in the region, the phenomenon is even more noticeable, according to Pirkanmaa officials. In addition to Tampere, sightings of the species have also been reported in central Finland.

The organism has since been identified as a Bryozoa or moss animal, a group of aquatic invertebrate animals. Last summer the Pirkanmaa centre for economic development, transport and the environment (Ely-keskus) called on members of the public to report sightings via its online invasive species portal (in Finnish).

"Moss animal colonies are spherical and stationary. To properly identify the species, you must attach a photo to your report," said Sami Moilanen, a water management specialist with the Pirkanmaa Ely-keskus.

The moss animal (Pectinatella magnifica) is an inland water species that requires temperatures of 12 degrees or warmer to flourish. However colonies tend to die off when water temperatures cool. The species thrives in warm, nutrient-rich waters and is generally seen in August and September.

First seen 20 years ago

During late summer and autumn, the moss animal forms reproductive pods that can be carried to new areas by waterfowl and ballast water.

Bryozoa colonies generally attach themselves to marine flora, shoreline stones or even jetty structures, but they can become detached and float in the water. Shallow water that is not stagnant provides the ideal growing conditions for the aquatic life form.

Last summer Finnish researchers working with their Estonian and Swiss peers attempted to determine the origin of moss animals detected in Lempäälä and Pirkanmaa, however they drew a blank.

The species is considered invasive in Finland and was encountered in waterways in Vuoksi in the Karelian region as far back as 20 years ago. Experts have speculated that the moss animal spread from that area in ballast waters from freighters in the region.

"After the summer of 2016 it was sighted outside the Vuoksi water system, first at Kirkkojärvi in Lempäälä and also in the southern part of Pyhäjärvi in Pirkanmaa in 2018 and 2019," Moilanen pointed out.

Halting the spread of invasive species

Pirkanmaa officials said that combating the spread of the invasive species is challenging because it makes inroads rapidly. Efforts can be made to contain the spread of the animal by clearing colonies from affected waterways or jetties as early as possible, or before they begin to produce reproductive cells, which appear as small black dots in the insides of colonies.

The Ely-keskus has recommended placing the animals on land, where they die easily and can be composted or buried. Local authorities may also reduce the likelihood of colonies forming by clearing beaches of potential anchors for the animals, such as dried branches and beached aquatic plants. It also called for owners to check fishing gear and boats to ensure they do not provide a foothold for the invasive species.

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