On Sweden’s west coast lies the Western Sea with Sweden’s saltiest water and the largest marine biodiversity. The Western Sea includes both Kattegat, Skagerrak, and the Øresund and is home to species such as mackerel, kelp, octopus, sea stars, corals, dolphins, and a total of 17 species of sharks.
Skagerrak, located furthest north in the Western Sea, is home to about 1500 animals and plants, thanks to the high salinity of the seawater, around 35 parts per thousand. Together with the Väderöarna Nature Reserve in the archipelago of Bohuslän, Kosterhavet is one of Sweden’s most species-rich marine areas. Several fjords in Bohuslän are considered so valuable that they are classified as Natura 2000.
However, as you move further south along the west coast, the water becomes fresher due to inflows from rivers, streams, and brackish water from the Baltic Sea. In Kattegat and around Øresund, the salinity is only around 15 parts per thousand. Salinity largely determines which species can thrive in the sea. This results in the number of species in the less salty Kattegat being only about half of that in the saltier Skagerrak.
Since 2009, Kosterhavet has held the title of Sweden’s first marine national park. The varying depths, high salinity, deep hard bottoms, and coral reefs in Kosterhavet are unique habitats for Sweden, contributing to a rich biodiversity of approximately 12,000 species. Moreover, there are around 200 animal species and nine algal species that exist only in Kosterhavet.
The salty and cold deep-sea water that enters from the Atlantic, through Kosterfjorden’s deep trench at 250 meters depth, allows deep-sea animals to live close to the coast. This also provides unique conditions for unusual sponge animals, corals, stingrays, sea pens, sea anemones, and bryozoans to coexist. The national park is also home to the largest population of harbor seals in the Western Sea, studied by researchers since the 1970s.
Gullmarsfjorden is a Natura 2000 area with unique marine life, attracting both divers and researchers. In 1983, Gullmarsfjorden, or Gullmarn as it is sometimes called, became Sweden’s first marine protected area, bordering several nature reserves on land. The fjord is 25 km long, 1–3 km wide, and Sweden’s only threshold fjord, meaning the threshold at the mouth is shallower (around 40 meters) than inside (up to 120 meters). This affects the exchange of water with Skagerrak, creating a distinct thermocline between the salty bottom water from the Western Sea’s depths and the fresher surface water from the Baltic Sea, Øresund, and local runoff.
The environment in Gullmarsfjorden has been well-documented, with scientific studies conducted since the 1830s. Today, several research stations at Gullmarsfjorden allow close observation of small organisms such as krill and coral, as well as a local cod population.
Between Sweden, Norway, and Denmark lies another Natura 2000 area, Bratten, the largest marine protected area in Skagerrak. The over 1,000 square kilometers area is characterized by deep hard and soft bottoms, valleys, and holes believed to have formed through gas leakage from the Earth’s crust. In Bratten, Sweden’s deepest marine area at 560 meters is found. Many rare fish and invertebrates inhabit Bratten due to its unusually deep hard bottom environment. Protected species like deep-sea corals, sponge animals, sharks, stingrays, rabbit fish, and halibut are present. Despite the area being protected, bottom trawling is still allowed in large parts of Bratten, and it is an important area for fishing North Sea shrimp and large fish on the deep mud bottoms.
The Western Sea faces several challenges, with fishing and overfishing being among the most significant. Fish stocks have drastically decreased over the last 100 years. The situation is most severe for cod in Kattegat, but many bottom-dwelling fish have also declined so much that predicting their future is difficult. The decline in cod has led the International Council for the Exploration of the Sea (ICES) to recommend a complete halt to cod fishing in recent years.
There are particularly few old, large cod capable of producing high-quality eggs and larvae in the Western Sea. The disappearance of large fish can affect other parts of the food chain through trophic cascades. Along the coasts of Skagerrak, the lack of large fish is believed to contribute to shallow bays filling with filamentous algae and eelgrass, which serves as a nursery for, among other things, fish fry, disappearing. This can lead to loss of species for the entire ecosystem. In Øresund, on the other hand, trawling has been prohibited since the 1930s, resulting in a more normal distribution of cod sizes in the area.
The situation regarding pollutants is in many ways better on the west coast than in the Baltic Sea. Dioxin levels in herring from the west coast have decreased since the 1990s and are safe to eat. However, in some cases, the development is heading in the wrong direction. Mercury in cod is increasing in Kattegat, and the levels of the perfluorinated substance FOSA and arsenic are higher in herring in the Western Sea than in other marine areas.
Painting boats with bottom paint containing organic tin compounds is a serious problem in the Western Sea, despite being prohibited in both Sweden and the EU since the 1990s. The toxins still exist in sediments from shipping lanes and harbors. Thanks to the ban, these substances have decreased somewhat in recent years, but they seriously harm marine life as they are toxic even at low concentrations. For example, snails have been found to develop reproductive organs of both sexes when exposed to toxins from bottom paint.
Some areas along the west coast show signs of eutrophication. This occurs in places where the nutrient load from the land is high, and water exchange is limited. However, nitrogen levels have decreased since the 1990s, suggesting that measures to reduce nutrient input have been effective. But the disappearance of cod has shown to have as much eutrophication effect as nutrient loading.
Like the Baltic Sea, toxic algal blooms also occur on the west coast, primarily caused by dinoflagellates. In some cases, for example, blue mussels can become inedible when these algal toxins accumulate. Some dinoflagellates can also illuminate the water through a phenomenon called bioluminescence. It occurs in late summer and is not harmful on the west coast, but in the Baltic Sea, it can be toxic.
Due to the changing marine environment and increased transportation, the Western Sea has gained new species in the form of alien and invasive species. Alien species are those that have spread outside their natural range with human assistance. Some of these are considered invasive as they can cause problems. In marine environments, foreign species often find their way to new locations through ballast water taken on board in one port and discharged in another. Some examples of foreign species in the Western Sea are the comb jelly Mnemiopsis leydyi, the Japanese giant oyster, and the Sargasso snare. They can take over large areas and disrupt the biological diversity.
The government wants to remove the Environmental Code's ban on nuclear power in virtually all Swedish archipelagos. This would open the way for nuclear power plants in Bohuslän, Öland, Gotland, and the Stockholm archipelago, among other places.
The documentary “Secrets of the West Coast” was awarded the prize for best photography and the Estonia Fund's special prize at the Estonian nature film festival MAFF, Matsalu Nature Film Festival in Lihula, this weekend. In addition, the film was recently named Best Nordic Nature Film at the German Green Screen festival in the town of Eckenförde on the Baltic coast. The festival is considered the most popular nature film festival in Europe, with nearly 400 nature films on the program.
All parts of the oceans are under triple attack, according to the EU's Copernicus Climate Service's major annual ocean report. ‘These changes affect us all – ecosystems, society and the economy,’ says oceanographer Karina von Schuckmann.
In an impact assessment, the Västra Götaland County Administrative Board has proposed a total ban on diving in six different areas within the Swedish Marine National Park Kosterhavet and the Väderöarna Natura 2000 area. The aim is to protect the few remaining eye corals that can be found at depths of between 80 and 120 metres. However, the proposal has stirred up deep emotions.
Even the ancient Greeks held the yellow-striped mullus – or, in short, the mullus – in high regard. With rising sea temperatures, it has been appearing on the Swedish west coast in autumn for several years now. However, spawning and reproduction have never been recorded in Swedish waters. But there are many indications that the mullet can now be considered a resident and reproducing species. Many shallow bays along the west coast have been swarming with its fry this summer.
The Swedish name is St Pers fish, named after the apostle Peter and has a false eye to confuse predatory fish. In the Mediterranean, it is a popular food fish. But now it has arrived here in Sweden. At a depth of 20 meters in Gullmarsfjorden on the Swedish west coast, Deep Sea Reporter encountered a most ordinary and spectacular fish: the John Dory.
In the fall, we reported on the sensational return of the blue mussel along the Swedish west coast. The mussel beds have spread to an extent where we have to go back in time to find an equivalent. But this has also created conditions for another species that feeds mainly on mussels - the common starfish, Asterias rubens. They have now invaded the mussel beds in an almost explosive way. And they have been joined by other species in the clam feast. Clams have a sophisticated way of escaping from predators, but starfish, on the other hand, have developed a counter-weapon. Join us on the battlefield of the west coast!
There have been rumours of large mysterious jelly balls floating around in the sea. For a long time, they have puzzled scientists. From northern Norway to the Mediterranean, around 100 records have been made since 1985. And three of these in Sweden. Our underwater photographer Tobias Dahlin has now made a fourth find, in the Gullmarsfjord in Bohuslän on the Swedish west coast, and he had his camera with him. We also meet Halldis Ringvold, a Norwegian marine biologist, who in 2021 revealed what's really hidden inside the meter-long wondrous balls.
On Sweden's west coast lies the Western Sea with Sweden's saltiest water and the largest marine biodiversity. The Western Sea includes both Kattegat, Skagerrak, and the Øresund and is home to species such as mackerel, kelp, octopus, sea stars, corals, dolphins, and a total of 17 species of sharks.
Researchers have now established that the harbor seals in the Kosterhavet area are becoming increasingly scarce. Last year, only half of the females gave birth to pups. This is according to research from the University of Gothenburg, following this year's seal count. – We were very surprised. These low numbers cannot be dismissed year after year, says Karin Hårding, professor of zoological ecology at the University of Gothenburg and the leader of the project.
In 2023, relatively many lobsters were caught in the Swedish and Norwegian waters, but this was not because the number of lobsters has increased, on the contrary.
When two large wind farms were planned in the sea on the Swedish west coast, the shrimp fishermen became worried that they would no longer be able to trawl for shrimp. The trawlers managed to get the Uddevalla municipal board involved in the unrest and together they started a campaign they called "Save the shrimp". The only question is – which shrimp and from whom should it be saved?
Indeed, we do have sharks in Sweden. Perhaps up to 17 different species! Some are, of course, very rare visitors to Swedish waters, while others live their entire lives in the same place.
On the rocks in Bohuslän live small, discreet shells with special properties. Snail-collecting scientists have now received clues about what is crucial for species' survival.
He has been seen in several places along the Swedish coast in recent days, but suddenly the alleged spy whale Hvaldimir appeard in the middle of Gothenburg's harbor.
The beluga whale that caused a stir in Hunnebostrand could be Hvaldimir – a Russian "spy whale" that escaped from a mission, reports P4 Väst.
Planting new eelgrass in places where it had disappeared can do the trick for wildlife. About 80 percent of the invertebrates have returned in a project on the West Coast
80 years ago, the submarine Ulven sank in Gothenburg's archipelago. Hitler's mine meant the death of 33 Swedish sailors. Now the victims are being honored by both the Swedish Defence Force and relatives.
The Japanese Oyster is larger than our domestic variety, and its edges are so sharp that medical services on the west coast have issued warnings to bathing tourists.
Mattias Sköld is a researcher at SLU Aqua in Lysekil. He has been involved in filming the seabed in marine protected areas, including in Bratten, on behalf of the Norwegian Sea and Water Authority (HaV).
In the laboratory's aquariums, lush corals glow ghostly white in the dark. But out in the sea, below the surface, there is almost only gravel and dead skeletons left. Here are the scientists who will save Sweden's last coral reef.
The film "What have we done?" which shows man's ruthlessness towards our oceans was praised and named "Honorable mention" in the international competition DPG/Wetpixel Masters 2022.
A vessel fishing in the Skagerrak caught a very unusual catch on Monday. The fishermen had caught a shark that none of them recognized. It finally turned out to be a bluntnose sixgill shark
Six experienced underwater photographers join forces and film and photograph the unique underwater world. You visit the mythical Persgrunden and several places around Koster. Several of the divers have dived here before, but that was a long time ago
