Researchers Discover 20 New Species of Sea Lettuce in the Baltic Sea Region

Sea lettuce, which is a type of green alga, grows along the coasts and is interesting as a potential food source. A new survey shows that there are 20 different species of sea lettuce along the Swedish coast. Credit: Sophie Steinhagen

The diversity of the sea lettuce species, a type of green algae, present in the Baltic Sea region and Skagerak, is significantly more extensive than previously believed. A comprehensive study conducted by researchers from the University of Gothenburg, surveying over 10,000 kilometers of coastal area, has identified a total of twenty distinct sea lettuce species.

Belonging to the genus Ulva, sea lettuce is a prominent species of green macroalgae, scattered widely across the vast Baltic Sea region, stretching from the Atlantic waters to the Bay of Bothnia in the Baltic Sea. Owing to its rapid growth and easy reproduction, sea lettuce has piqued the interest of the growing aquaculture industry. Research is ongoing both in Sweden and abroad for utilizing sea lettuce in the food industry and for different biochemical applications.

There are multiple species, but until now it has not been known how many there are and previously only a handful had been identified.

Invasive species identified

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

The researchers also found completely new species of sea lettuce in Swedish waters that have not previously been described scientifically. Some of these appear to only grow in the Baltic Sea.

Sophie Steinhagen, a marine ecologist at the Department of Marine Sciences at the University of Gothenburg. Credit: Björn Larsson Rosvall

The importance of this survey is significant. Growing sea lettuce as a food source is a rapidly increasing industry, and foreign species risk being spread through simple ignorance. To maintain and protect valuable ecosystems along the coasts, it is important to know which species grow there and to not introduce new species that risk out-competing the native species.

Grow the right species in the right place

“Our study shows that today’s method of identifying species, which is often done by looking at the appearance of green algae, is insufficient for identifying the distribution of the various species. We have not been able to see the real extent of the biological diversity,” says Steinhagen.

The inventory discovered many new species, information that can be valuable when cultivation of sea lettuces is initiated in new places along the coast. It is important to grow the right species at the right place to avoid the risk of impacting diversity.

“This new knowledge allows us to develop methods for maintaining the unique sea lettuce species along a specific coast. Our survey can also help when writing regulations related to 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 the green algae Ulva. In Sweden, sea lettuce grows on cliffs and rocks at the edge of water along the entire West Coast and in the Baltic Sea up to the Bay of Bothnia. Sea lettuce is very nutritional with relatively high protein content, healthy polyunsaturated fatty acids, and dietary fibers. It also has valuable biochemical molecules. Research is ongoing both in Sweden and abroad for utilizing sea lettuce in the food industry and for different biochemical applications.

Reference: “Molecular identification of the ubiquitous green algae Ulva reveals high biodiversity, crypticity, and invasive species in the Atlantic-Baltic Sea region” by Sophie Steinhagen, Samanta Hoffmann, Henrik Pavia and Gunilla B. Toth, 5 May 2023, Algal Research.
DOI: 10.1016/j.algal.2023.103132