Spanish research examines how harmful algal bloom species thrive

A team from the Oceanographic Center of Vigo, part of the Spanish Institute of Oceanography (IEO-CSIC), has presented a study focused on microalgae responsible for harmful algal blooms (HABs), which are common in the area and can impact public health and shellfish harvesting.

Specifically, the study analyzes how Alexandrium minutum, Dinophysis acuminata, and Pseudo-nitzschia spp.—which produce paralytic (PSP), diarrhetic (DSP), and amnesic (ASP) toxins, respectively—affect the ecosystem and different phytoplankton species in the Rías Baixas.

The research has been published in the journal Harmful Algae and involved collaboration with the University of Vigo and the French Research Institute for Exploitation of the Sea (IFREMER).

A device called the “Fine-Scale Sampler,” developed by IFREMER, made it possible to collect 15 samples and detect ocean structures and organism aggregations that usually go unnoticed in conventional monitoring programs. These results will help improve early warning systems and the management of preventive closures in shellfish harvesting.

Results

The microalgae D. acuminata and Pseudo-nitzschia mainly grow during coastal upwelling, a process in which deep, nutrient-rich waters rise to the surface. They also grow better when the water forms layers based on temperature.

Meanwhile, A. minutum is more common in sheltered coastal areas and increases after heavy spring rains. This happens when a warmer, less salty surface layer forms, distinct from the water below. However, it does not grow alone and must compete with other species that are also well adapted.

"The description of the fine vertical structure of the water column and the formation of multiple microhabitats, separated by just a few tens of centimeters, is key to understanding how phytoplankton species with different adaptations can coexist while using the same resources," explained Velasco Senovilla, lead author of the study.