Predicting the Arrival of the Portuguese Man o' War

Scientists are studying how winds, currents, and climate change influence the drift of the Portuguese man o' war in an effort to forecast its seasonal movements

A team of marine scientists have launched an ambitious campaign to understand and predict the movements of one of the ocean’s most eye-catching and feared drifters: the Portuguese man o' war (Physalia physalis).

Though often mistaken for jellyfish, the Portuguese man o' war is a floating colony of specialized organisms that sails on the ocean surface, powered by wind and guided by ocean currents. Its striking blue float and trailing tentacles make it easy to spot, and to avoid. A single sting can be extremely painful, and in rare cases, dangerous to humans.

The Portuguese man o' war is one of the most distinctive species in the neuston, the community of life that drifts at the ocean’s surface. In recent summers, sightings in the Cantabrian Sea along Spain’s northern coast have become increasingly frequent, occasionally resulting in beach closures during the busy summer season. Scientists suspect that climate change and warmer waters may be driving these occurrences farther north, but predicting where and when they will appear has remained a challenge.

To address this, the team is combining fieldwork with advanced oceanographic tools to understand how environmental factors influence the species’ movements. Researchers working alongside local coastal rescue teams, the Spanish Institute of Oceanography in Gijon, the Asturias Marine Observatory, and the University of Oviedo’s School of Civil Marine Studies, are locating and recovering specimens at sea in a region in north Spain, Asturias.

Captured man o' wars are temporarily maintained under controlled conditions at the BIOPARC Gijón Aquarium, which provides facilities and expertise for studying delicate marine organisms. These specimens allow scientists to examine their population structure, feeding behavior, and movement patterns.

At the same time, the team are deploying satellite-tagged, 3D-printed floating models that replicate the man o' war’s drift across the water’s surface. These models will help researchers better understand how winds, waves, and currents transport man-of-war over large distances, a key step toward developing accurate forecasting models.

Experiments and model deployments will also take place in other ocean regions, including the Bermuda Atlantic Time-series Study (BATS) and the Hawaii Ocean Time-series (HOT) sites, where the Portuguese man o' war are more commonly found. These international comparisons will provide valuable insight into how global ocean conditions influence their distribution, and how winds and currents drive their movement in the ocean.

Ultimately, the campaign aims to improve scientific understanding of what drives the Portuguese man-of-war’s seasonal movements and to develop predictive models that can anticipate their arrival, initially for Spanish beaches. These forecasts could help coastal managers, rescue services, and the public take preventive measures, reducing the risk of stings and ensuring safer enjoyment of the region’s beaches. Future implementations, however, can be developed for any region in the world, since the developed models are not specific for a region and can be fed with the local wind and sea conditions.

“The most exciting part for me is that this project brings together pure science and engineering, with a model that can, and will, be used for real societal benefit. We are used to seeing Portuguese man o' war here in Bermuda, but the ones showing up in higher latitudes are much larger than ours and can pose a real threat to both adults and kids. At the same time, we are not exactly sure what the future holds for places like Bermuda regarding these beautiful animals, so having a model already in place to help with decision-making is a great ace to have up our sleeve,” says oceanographer Leocadio Blanco-Bercial who is involved in the project.

The Physalia Asturias campaign, running from June to September, is led by members of the Biodiveristy and Ecology of Marine Ecosystems (BEME) research group at the Gijón Oceanographic Center of the Spanish Institute of Oceanography (IEO-CSIC), and of the Marine Ecology and Biogeochemisty Group at the University of Oviedo, with support from Asturias’s Sekuens through a Grupin Grant, and the Spanish State Research Agency (AEI) from Spain’s Ministry of Science, Innovation and Universities. This effort is part of the broader project PHYSALIA – Evolution of Biological Navigation – which brings together researchers across Spain, Europe, and the Americas, including the University of Las Palmas de Gran Canaria, the Institute of Marine Sciences of Andalusia (ICMAN-CSIC), the Balearic Islands Coastal Observation and Prediction System (SOCIB), the Pontifical Catholic University of Valparaíso in Chile, the Joint Research Center (JRC) of the European Commission, and at Arizona State University Bermuda Institute of Ocean Sciences.