In the fall of 2022, Península Valdés was the scene of an environmental disaster: 30 southern right whales were found dead on the coasts of Chubut within a few weeks. At the same time, a massive die-off of South American sea lions (Otaria flavescens) was recorded in the Golfo Nuevo.
The initial suspicion pointed to a harmful algal bloom, known as “red tide”, but scientific evidence was lacking to explain how the toxins reached the large marine mammals.
The scientific investigation
The work was carried out by the Centro para el Estudio de Sistemas Marinos (CESIMAR-CONICET) and the Instituto Argentino de Oceanografía (IADO-CONICET). The study, recently published, documents with field evidence the transfer of toxins throughout the entire food chain, from phytoplankton to marine mammals.
The bloom was dominated by dinoflagellates of the Alexandrium catenella/tamarense complex, producers of paralytic shellfish toxins. Researchers Valeria D’Agostino, Mariana Degrati, Ariadna Nocera, Valeria Guinder, and Carola Ferronato traced the path of the toxins through samples of phytoplankton, zooplankton, mussels, pelagic fish, and marine mammals collected in the Golfo Nuevo.
The role of mesozooplankton
One of the most relevant findings was the role of mesozooplankton as a critical vector in the transfer of toxins. The highest levels were recorded in areas where whales were actively feeding at the end of September 2022, just before the peak of mortality.
Southern right whales, which feed by filtering water, ingested the contaminated mesozooplankton directly, accumulating lethal doses. The study also detected toxins in fecal samples from live whales, demonstrating that part of the population survived with sublethal levels of contamination.
Sea lions and maternal transfer
The die-off of sea lions was associated with saxitoxins, highly potent neurotoxins. The most unprecedented finding was the detection of these toxins in fetuses of pregnant females, the first evidence of maternal transfer in the region. This indicates that exposure reached even gestating offspring.
Impact on human health
The study incorporated data from the hospital of Puerto Pirámides and the Harmful Algal Monitoring Program of the Chubut Fisheries Secretariat.
During the bloom, approximately 10% of the local population sought consultation for gastrointestinal symptoms. Although no direct causal link was established, the temporal coincidence highlights potential implications for public health.
A message for the future
The researchers warn that, with climate change, harmful algal blooms may become more frequent and intense, increasing the risk for marine fauna and human communities. The study underscores that microscopic processes, such as the proliferation of dinoflagellates, can have devastating consequences for the largest animals in the ocean.
The work of CONICET provides unprecedented evidence on how red tide toxins travel through the food chain and cause massive die-offs. The research not only explains what happened in 2022 but also warns of the need for constant monitoring and prevention policies to protect both marine biodiversity and human health in scenarios of environmental change.
