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Topic: Sea vomit

This tunicate originates from Japan and forms large colonies on the seabed. It can be devastating for animals and algae at the bottom. The species was first discovered in Norway in December 2020 when divers found it at Engøy near Stavanger. 

As the Norwegian name “havnespy” implies, Didemnum vexillum often establish in ports, on small boats and dock pilings. Most likely, Sea vomit is often transported by means of shipping traffic. Among other things, the sea vomit can grow on ship hulls, or floating objects such as ropes, floating docks and buoys.

Sea vomit makes colonies that can grow very quickly because it can clone itself. A colony can elevenfold the size in 14 days. Sea vomit creates dripping colonies in which small pieces of the colony fall and make new colonies nearby, or that are taken by the current and settle in new places. This species is also called pancake batter tunicate, or carpet sea squirt because when the species reaches an area, it can quickly cover the seabed. It can displace other species and be destructive to the bottom community. 

The Sea vomit can withstand temperatures down to minus 2 degrees Celsius, but it needs 11–14 degrees in the water to produce larvae. That means that in the north of Norway, it probably fails to spread with larvae, but it can still spread with shipping and reproduce with the help of fragments.

In Norway, we find mostly sea vomit between 5 and 20 meters deep, but in Canada the Sea vomit has been found down to a depth of 65 meters. It also needs a salinity of over 20 psu. This means that it is difficult for sea vomit to establish themselves in brackish water, and it will therefore probably stay under the brackish water layer in the Norwegian fjords.