Invasive jellyfish and comb jellies are being transformed into sustainable agricultural fertilizer

During the summer months, the increase in invasive species along the Adriatic Sea coast, especially on the shores of Croatia, has now become a common occurrence. The comb jellies, first recorded in 2016 and known as the "sea walnut" (Mnemiopsis leidyi), have practically invaded in recent years, negatively affecting the marine ecosystem and local tourism. 2025 has gone down in history as a record-breaking period in terms of the frequency of these marine organisms being observed in Adriatic waters. Observations made in the western parts of Croatia during the spring months have revealed that these creatures consist of extremely large, nutrient-rich individuals that have successfully survived the winter and are ready to reproduce. In the mid-summer and early autumn periods, when sea water temperatures rise, the populations of these creatures are expected to peak, further increasing the pressure on regional marine life.

It is not only comb jellies but also the cup monster (Copa meduza) and jellyfish we are unaccustomed to that are causing a serious source of trouble for everyone interacting with the sea in the region. Across a vast coastline stretching from Pula to Piran, the constant presence of various jellyfish species is being reported by fishermen and bathers. This situation both excessively fills the nets of fishermen in the region, hindering their fishing activities, and negatively affects beach tourism, threatening the local economy. Local residents and officials are watching with growing concern each year as these overpopulated, sticky, and irritating marine organisms turn into a serious nightmare throughout the summer season. All economic and social activities intertwined with the sea appear to be in a serious bottleneck due to this biological invasion.

Scientists, arguing that these invasive organisms should not be seen merely as elements of destruction, have begun to develop a new eco-friendly strategy. An innovative project conducted by the Ruđer Bošković Institute Center for Marine Research in Rovinj is investigating how comb jellies and jellyfish can be transformed into a sustainable agricultural resource. To turn the overpopulation of these marine creatures and the environmental damage they cause into an opportunity, researchers are working on methods to obtain high-quality organic fertilizer from them. As part of the project, the idea of utilizing this large, salty mass that fills the nets and must be discarded by fishermen has been proposed. The team led by Dr. Tjaša Kogovšek is scientifically exploring ways to turn these creatures from useless waste into a renewable source of phosphorus.

The main goal of this innovative project is to produce a sustainable fertilizer using biomass waste obtained from the seas, thereby reducing agriculture's dependence on fossil fuels. The proof-of-concept phase of the project started on 30 June 2025 and, following a one-year study period, has now reached the completion stage. The research team has successfully managed to separate elements vital for plant development, such as phosphorus and nitrogen, from marine biomass in a controlled laboratory environment. The absence of any pollutants in the sludge or precipitate obtained through this method makes the resulting product an extremely safe and high-quality agricultural fertilizer. This success clearly proves how valuable a raw material source invasive jellyfish and comb jellies can be for the circular economy of the future.

The rapidly increasing global population and the parallel growth in food demand constitute one of the greatest challenges facing the agricultural sector today. Traditional chemical fertilizer production causes serious harm to the ecosystem by depleting the world's limited and non-renewable natural resources (such as phosphate rocks). Renewable fertilizers to be obtained from marine biomass will greatly contribute to the protection of the environment while also improving the soil structure. The primary goal of scientists in the upcoming period is to find investors who will scale up this laboratory-successful procedure to an industrial and commercial level. Thanks to this progress, growing produce such as tomatoes, peppers, and zucchini biologically with fertilizers obtained by purging the seas of invasive creatures will become a much more viable scenario in the future.