The findings of Croatian scientists on the phenomenon of the mass occurrence of marine mucilage in the northern Adriatic were published in the renowned journal Scientific Reports (Springer Nature). The research was conducted by scientists from the Ruđer Bošković Institute’s Center for Marine Research (CIM IRB), in collaboration with the Croatian technology company SeaCras and Algebra Bernays University, combining advanced field measurements, sensors, and satellite data analyses.
The study documented an episode of intense algal bloom and mucilage formation during 2024 in Istria, an event of a scale not recorded along the eastern Adriatic coast for more than two decades. The researchers explained in detail why this exceptionally pronounced event occurred, identifying the key meteorological and oceanographic conditions that preceded it, and they also determined and tracked the abundance and occurrence of the phytoplankton species involved in mucilage production.
“Such events can seriously disrupt marine ecosystems and directly affect coastal communities, from tourism and fisheries to overall quality of life, so understanding their causes is essential for timely warning and adaptation,” the scientists emphasize.
A phenomenon that “escapes” conventional monitoring
Although algal blooms are a natural and seasonal occurrence, changes in environmental conditions,such as rising sea temperature, reduced water mass exchange, and increased freshwater and nutrient inputs can lead to abnormal accumulations of marine mucilage. Such events have a significant impact on marine ecosystems, as well as on human activities including tourism, fisheries, maritime transport, and recreation.
The results showed that each phase of the large mucilage accumulations observed in 2024 was directly linked to exceptionally intense phytoplankton blooms, which played a key role in the formation and development of mucilage. At the same time, the diversity of plankton species within the mucilage aggregations during that period was reduced compared with typical seasonal blooms.
Heat, the Po River, and windless calm: a scenario that favoured mucilage
The study further demonstrated that mucilage formation was closely associated with rising sea temperature and sudden drops in salinity caused by increased freshwater inflow, especially from the Po River, creating environmental conditions conducive to mucilage development and accumulation. The mucilage aggregates themselves, connected into larger structures, ranged from elongated formations more than 20 kilometres long to locally migrating patches smaller than 20 metres.
What did satellites reveal and why does it matter for early warning?
A particular strength of this research lies in its combination of different technologies and high frequency measurements. CIM IRB scientists used ODAS oceanographic buoys located about 4 nautical miles off Rovinj, which continuously record physical and biological sea parameters, as well as advanced flow cytometric analyses that reveal how plankton community composition changes. SeaCras complemented the field measurements with its own AI based analyses of high spatial resolution satellite imagery, enabling more precise monitoring of the event’s spatial spread and dynamics.
“This level of temporal and spatial resolution allowed us, for the first time, to fully link changes in environmental conditions with the behaviour of plankton communities and the emergence of marine mucilage. This is a key step forward in understanding this complex phenomenon,” said Dr Daniela Marić Pfannkuchen, Senior Research Associate at the Ruđer Bošković Institute’s Center for Marine Research in Rovinj and the paper’s corresponding author.
“The Ruđer Bošković Institute and SeaCras public–private partnership has set not only new standards in operational oceanography, but also measurable indicators for our tourism and fisheries industries and, most importantly, for the local community and its people,” said Dr Mario Špadina, CEO of SeaCras and a co-author of the study.
The results are highly significant because marine mucilage can seriously affect coastal communities and the economy. Dense mucilage accumulations hinder fishing and damage nets, reduce the quality of the sea experience for swimmers, and negatively influence perceptions of seawater cleanliness during the tourist season. Understanding the mechanisms that lead to such events is crucial for developing early warning systems and adapting to the future impacts of climate change.
The Ruđer Bošković Institute’s Center for Marine Research is one of the region’s leading scientific centres for the study of marine ecosystems, while SeaCras is a Croatian company specializing in sea monitoring using satellite data and artificial intelligence. Together, they are developing advanced early warning systems based on the concept of a digital twin of the sea, seabed mapping, and applications in public health, with the aim of detecting and tracking pollutants such as microplastics, faecal contamination, and others.
With this approach, the Republic of Croatia demonstrates strong domestic scientific and technological capabilities and actively pushes boundaries and sets best practice standards for public-private partnerships, with potential for exporting high technologies.
