Gunilla B. Toth’s research while affiliated with University of Gothenburg and other places

Seaweed aquaculture is rapidly growing globally and offers environmental benefits such as reducing eutrophication and increasing biodiversity. Sweden has a long coast with favorable conditions for seaweed cultivation, but the current industry remains small. Over the past decade, several innovative research projects have explored and developed techniques tailored toward sustainable seaweed aquaculture. This study synthesizes recent advances in Swedish seaweed aquaculture research, highlighting innovations that support biomass yield and quality. We conducted a systematic review of 130 studies from the Thomson Reuters Web of Science, focusing on Swedish seaweed aquaculture research, and ultimately included 21 relevant publications from 1984 to 2025. The main seaweed species cultivated in Sweden are the brown seaweed Saccharina latissima and the green seaweed Ulva fenestrata . Key strategies to enhance biomass productivity, quality, and sustainability include optimizing land‐based juvenile preparation, careful selection of cultivation sites, and strategic timing of sea‐based harvests. Innovative approaches like the utilization of nutrient‐rich process waters from food production offer sustainable methods to boost yield and protein content, aligning seaweed cultivation with circular economy principles. Future development and optimization of cultivation protocols for other protein‐rich seaweed species (e.g., Palmaria palmata ) or species that tolerate lower salinity (e.g., Fucus vesiculosus or U. intestinalis ) will be critical to maximize the potential of Swedish seaweed cultivation, ensuring its effective contribution to food security and environmental conservation. As commercial interest in seaweed continues to grow, findings summarized here provide a robust foundation for the expansion of seaweed aquaculture in Europe and beyond.

The rising global significance of sea lettuce (Ulva spp.) in aquaculture stems from its versatility, rapid growth, and nutritional benefits. Cultivation expansion into lower salinity areas, like the Baltic Sea, is crucial for advancing aquaculture beyond traditional environments. This study investigated the impact of long-term (8 weeks) low salinity treatments on the biochemical content of eight Ulva strains – encompassing some of the most common Ulva crop species (Ulva lacinulata, Ulva linza, Ulva intestinalis, Ulva fenestrata) of the wider Baltic Sea area – from varying source salinities (30, 14, 9, 7). Most strains exhibited significantly higher growth rates and contents of crude protein under low salinity treatments, irrespective of where they came from (i.e. euhaline or mesohaline environments). However, effects on pigments and phenolic contents were strain-specific. Ulva lancinulata showed high resilience to salinity changes. Cultivating Ulva under low salinity conditions enhances its nutritional attributes and identifies the broader Baltic Sea as a viable cultivation environment. Nevertheless, careful selection of strains is crucial due to significant inter- and intraspecific differences. This research underscores the importance of tailored cultivation strategies for optimizing Ulva biomass production, particularly in the context of the expanding Blue Economy industry.

Correct species identification is fundamental for assessment and understanding of biodiversity. Erroneous species identification may impede conservation management and may delay detection of invasive species. The ubiqui- tous green algal genus Ulva is known for its wide environmental tolerance, plastic morphology, occurrence of cryptic species and ambiguous species concepts that hinder clear identification. We used molecular monitoring to assess species diversity and distribution of Ulva along the full Atlantic-Baltic Sea salinity gradient (> 10,000 km). Ulva specimens were collected from Denmark, Finland, Germany, Norway, and Sweden. DNA barcoding analysis of the tufA gene revealed 20 genetic entities in total, of which 11 could be identified to species level (U. californica, U. flexuosa, U. torta, U. linza, U. prolifera, U. fenestrata, U. australis, U. intestinalis, U. compressa, U. gigantea, U. lacinulata). Nine entities (Ulva sp. 1–9; [Ulva capillata]) yielded novel sequence reads that belonged to either unidentified species, species complexes, or singletons. At least 3 of the discovered species (U. australis, U. californica, U. gigantea) are considered non-native and potentially invasive. Furthermore, considerable differences between the observed and the historically estimated species distributions were found. The highest diversity was recorded in the Atlantic and Skagerrak region whereas only two entities of taxo- nomically accepted species where found north-east the Blekinge coast. Our study shows that the species diversity of Ulva in the study area is diverging from previous reports, and that molecular methods are imperative for species identification in this morphologically plastic genus. Furthermore, the presence of non-native species indicates a necessity for further fine-scale monitoring in specific areas to e.g. mitigate formation of green tides.