Twenty species of sea lettuce are found throughout the Baltic and Scandinavia

The number of species of sea lettuce, green algae in the Baltic Sea and Skamov region is much greater than previously known. Researchers at the University of Gothenburg surveyed 10,000 kilometers of coast and found twenty species of sea lettuce.

Green macroalgae of the genus Ulva, also known as sea lettuce, is almost ubiquitous in the greater Baltic Sea region and can be found from the waters of the Atlantic to the Gulf of Bothnia in the Baltic Sea. Sea lettuce reproduces easily and grows quickly, which makes it attractive for the growing aquaculture industry. Research is ongoing both in Sweden and abroad to utilize sea lettuce in the food industry and for different biochemical applications.

There are several species, but until now it is not known how many there are and previously only a few were identified.

Invasive species identified

“We have studied the biodiversity of the Baltic Sea, Kattegatt and Skagerak by taking a large number of samples from sea lettuce which we then analyzed for DNA. We found 20 unique species and subspecies. Three of them are invasive species that found their way here in various ways,” said Sophie Steinhagen, a researcher at the Tjärnö Marine Laboratory.

The researchers also discovered an entirely new species of sea lettuce in Swedish waters that had never before been scientifically described. Some of them seem to only grow in the Baltic Sea.

The importance of this survey is very significant. Growing sea lettuce as a food source is a thriving industry, and alien species risk spreading through simple ignorance. To maintain and protect the valuable ecosystems along the coast, it is important to know which species grow there and not to introduce new species that risk competing with native species.

Grow the right species in the right places

“Our study shows that current species identification methods, which often involve looking at the appearance of green algae, are not sufficient to identify the distribution of various species. We haven’t been able to see the true extent of biodiversity,” said Steinhagen.

The inventory uncovered many new species, information that can be valuable when sea lettuce cultivation is started in new locations along the coast. It is important to grow the right species in the right places to avoid the risk of affecting diversity.

“This new knowledge allowed us to develop methods for cultivating unique sea lettuce species along specific coasts. Our surveys can also help when writing regulations regarding invasive species that should not be used in aquaculture if it is to be sustainable,” says Steinhagen.

Facts about sea lettuce

Sea lettuce consists of many species of green algae Ulva. In Sweden, sea lettuce grows on cliffs and rocks by the water along the West Coast and in the Baltic Sea to the Gulf of Bothnia. Sea lettuce is highly nutritious with a relatively high protein content, healthy polyunsaturated fatty acids and dietary fibre. It also has valuable biochemical molecules. Research is ongoing both in Sweden and abroad to utilize sea lettuce in the food industry and for different biochemical applications.