Investigating the causes of algal blooms

Toxins from HABs are harmful to fish and shellfish and can be lethal to humans if such contaminated seafood is eaten. Therefore, HABs can have serious economic consequences for local fishermen and tourism. The AQUALIGHT project addressed this problem, investigating the presence of HABs in Alfacs Bay, a tidal estuary in the north-west Mediterranean.

Scientists combined observations with 3D models to understand the processes behind bloom formation in the Bay. Researchers also identified which environmental conditions encourage bloom development and the phytoplankton species involved.

Computer models were developed to study small-scale processes such as the mixing of the water column due to turbulence, and light availability. A model was also set up to determine the validity of current methods for measuring phytoplankton growth and productivity.

Scenarios for different meteorological conditions were created that showed that under low wind conditions Alfacs Bay experienced typical estuarine circulation. This reduced the residence time of phytoplankton in the bay, which decreased the likelihood of a HAB.

However, high wind speeds caused normal estuarine circulation to break down, increasing residence time and the possibility of a HAB occurring. This is because Alfacs Bay is high in nutrients compared to the open sea, and a longer residence time means better growth conditions for phytoplankton.

Knowledge gained through AQUALIGHT will help scientists make predictions and establish early warning systems for HABs. This will enable policy makers to make informed decisions that help reduce the economic impacts of toxic blooms on the local fishing and tourism industries.

Furthermore, as HAB events occur across the globe, the scientific insights gained through the work of AQUALIGHT can help all communities that face recurring HAB outbreaks.