"Mussel farming is a rapidly growing field. We are soon reaching a stage where it could become economically viable," says Jonne Kotta, a marine ecology professor at the University of Tartu's Estonian Marine Institute. Currently, aquaculture in Estonia primarily involves trout farming, but at the experimental farm in Tagalaht, Saaremaa, Kotta and his colleagues are also testing the cultivation of mussels and bladderwrack.

One participant in the experiment, Indrek Adler, a junior researcher at the Estonian Maritime Academy and a professional coastal fisherman, notes that mussels in Tagalaht have considerable potential. Although these mussels remain smaller than those grown in saltier waters, they are known to have a better meat-to-shell ratio. "In saltwater mussels, the shell accounts for about 80 percent of the total weight, whereas here, it's about 48 percent – meaning 52 percent of our mussels' weight is meat," Adler explains.

In aquaculture, Jonne Kotta highlights two main approaches: traditional fish farming and an environmentally restorative method. The latter approach involves cultivating mussels and large algae. "The more mussel farms we establish, the more nutrients we remove from the Baltic Sea, improving its overall condition," explains Kotta.

Although the Baltic Sea is often labeled as polluted, Kotta suggests distinguishing between two types of pollution: toxic contamination and nutrient overloading. Thanks to international cooperation, levels of harmful, toxic compounds have significantly decreased in the Baltic Sea. However, the problem of excess nutrients remains unsolved. "Polluted might not be the most accurate term. Nutrients could be seen as pollution in some contexts, but in reality, they're a type of fuel that can be harnessed," adds Indrek Adler.

As a fisherman, Adler became interested in potential ways to improve the condition of the Baltic Sea. Through his research, he found that Estonia could benefit from restorative aquaculture by cultivating three species: sea lettuce (Ulva intestinalis), edible mussels and the free-floating form of bladderwrack (Fucus vesiculosus). Adler's team is now experimentally cultivating the latter two in Tagalaht.

Both researchers emphasize that mussel size depends on seawater salinity. "Since our coastal waters have lower salinity than ocean water, mussels here grow more slowly and remain smaller," notes Kotta. Even within Estonian waters, not all bays are the same; the waters along the western coasts of Saaremaa and Hiiumaa are saltier than in the eastern Gulf of Finland. The research team has now determined that, given the conditions off Saaremaa's coast, the optimal cultivation period for a mussel crop is about 18 months. "You can also cultivate mussels for 24 months, which will result in a noticeably larger size, but the meat-to-shell ratio doesn't improve significantly," Adler explains.

Like harvesting potatoes, mussels are best collected in the fall rather than the spring. According to Adler, mussels are natural filters, optimally processing nutrients from water at temperatures between 15 and 22°C. "A mussel grows to about 1.5 centimeters here and can filter around four liters of water per hour," he points out. Mussels stop filtering in water over 25°C, while in winter, they enter a kind of dormancy, subsisting on micro-particles accumulated during summer. "A hungry mussel is generally not as tasty as a well-nourished one," Kotta adds.

According to Indrek Adler, mussel farming holds great promise in Estonia because the species is abundant in local coastal waters. "We know the methods needed to cultivate mussels in the Baltic Sea. Now, my goal is to solve the economic side of this cultivation," he says, outlining his future plans. Larger mussels are easier to process for their meat, but Adler is working to develop industrial methods that can add value to Estonia's smaller mussels.

One method he has tested involves crushing and settling the mussels. "We first crush fresh or frozen mussels, then use water to separate the meat. The shell is pure calcium carbonate, which settles quickly, while the meat is airy and light," Adler explains. However, he finds this method less than ideal; in an attempt to streamline the settling process with his colleagues, they lost a significant amount of valuable protein. Another method currently being tested is micronization, or fine grinding. According to Adler, this approach is better, as it requires less water than settling.

"The biomass of mussels is highly nutritious," says junior researcher Indrek Adler. In addition to their high protein content, mussels have beneficial properties that make them suitable for sports and functional drinks. Mussel meat also has known anti-inflammatory effects. The research team has already investigated extracting both proteins and carbohydrates from local mussels.

"We can isolate high-value components, but to get mussel farming up and running, we first need to address the volume issue," Adler explains. He estimates that to make a noticeable impact on the Baltic Sea's condition, tens of tons of mussels would need to be farmed. By comparison, Swedish mussel farms currently produce an average of 70 to 150 tons of mussels annually. Mussel farming in Estonia would become economically viable if a large market and applications for such a mass of mussels could be found.

"We've been examining mussels primarily as food for humans and pets," adds Jonne Kotta. For mussel farming to be financially sustainable, he suggests focusing on sectors with higher profit margins. "Product marketers know well that we're always willing to spend significant amounts on children and pets," he says.

The research team is still in the lab, developing industrial-scale processing methods for mussels, but both researchers agree that the next step is to secure investors. "In my view, a tripartite collaboration is needed to get green blue-economy projects like this off the ground," Adler points out. In other words, support should come from the government, research institutions and the private sector.

At the national level, Adler believes that regulations concerning the blue economy are outdated. "If someone wanted to set up a mussel farm today, the application process would take about two years, with no guarantees at the end," he explains. First, he suggests a clear distinction between trout farming and restorative aquaculture, such as mussel and algae cultivation. Second, officials from the Ministry of Climate and the Ministry of Regional Affairs, along with specialists, could create a roadmap outlining Estonia's potential for restorative aquaculture.

"Of course, mussel farming won't solve all the Baltic Sea's problems, given the high nutrient levels in the water," Kotta acknowledges. However, he considers this encouraging news for the industry, as mussel farmers won't need to worry about declining yields over the next 50 to 100 years: "The nutrient reserves are simply so vast."

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