Nudibranchs fill the sea with colours and shapes
They look like small mythical creatures or underwater butterflies and they thrive along the Swedish West coast. They have some fascinating Swedish names, too. They are not just any old slugs, either - they are naked slugs which have shed their shells and now fill the archipelagos with wonderful colours and shapes.
Below the surface of the sea on the west coast live some remarkable gastropods with fantastic shapes and colours. They are called sea slugs, after shedding their shells at the larva stage. Instead they protect themselves by having a foul taste or stinging protrusions on their back. These protrusions contain nettle cells they take from the nettles they eat. If you should decide to kiss one of these slugs, your lips will really sting!
Nudibranchs give us plenty of warning with their colours that we should keep a safe distance, which generally works with hungry fish but not curious marine biologists. Diving equipment is normally required to study these slugs, even though some species can be seen very close to the surface.
There is something strange, almost unearthly about them; they are rather like some kind of mythical sea creatures. They look so strange, with their odd shapes and colour. They appear and then disappear. "Looking for nudibranchs is a little like looking for funnel chanterelles – they seem invisible but once you have got the eye for them, you are almost surrounded by them," says Kennet Lundin, biologist at the Gothenburg Museum of Natural History.
The West coast - a paradise for nudibranchs
The real paradise, with the largest number of different species, is found deep underwater on the rocks at the edge of the outer archipelago, where the water is cold and there are many currents. It is there the nudibranchs find their favourite food: polyps and mosses.
Places near Väderöarna, Smögen and the estuary of Gullmarsfjorden can literally be swarming with nudibranchs, particularly in the spring. Because they are so numerous, they probably have a significant impact on the marine ecosystem on the coast and may affect the number of jellyfish, for example, since they feed on jellyfish polyps.
More knowledge through international awareness
Since 2010, Kennet Lundin and the biologist and underwater photographer Klas Malmberg have run a project to raise awareness of nudibranchs in Sweden, and they hold courses on the subject at a number of diving centres. They are building up a reference collection at the museum in collaboration with other international researchers.
At present there are 95 known species on the west coast, of which Kennet and Klas have found around fifteen that are new for Sweden, as well as a number of species that have not been seen for many years. Some are entirely new species for science! A new species for Sweden was discovered in May this year which has been named stjärnkottnuding, after the star-shaped protrusion by the main tentacles.
Completely new species
The group of kottnudingar (dotidae) have been given their name from the protrusions on their back that look rather like fir cones. Kennet and Klas discovered a completely new species that has a ring-shaped dark line by the edge of the section next to the main tentacles. It was given the working name of kajalkottnuding. They were also told that a DNA search indicated a presumed rygghorning which they had discovered in 2015 by Lysekil, next to the naturist beach at Släggö, is actually a new and previously unknown species. Rygghorningar are a group of nudibranchs that have been named after the dorsal protrusions that look similar to cow horns.
At the time of writing this species has not yet been given a Swedish name. But there is more to find out there and more species will be discovered!