Harmful Algal Blooms on the Portuguese coast: Cross-checking events with remote sensing ocean colour data for coastal management

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Phytoplankton plays a vital role in marine ecosystems, serving as a primary food source for a diverse array of organisms, including commercially important bivalves, crustaceans, and fish. However, in some situations, the proliferation of algae can cause serious economic losses for aquaculture, fishing, and tourism and have major environmental and human health impacts. Increases in the occurrence of toxic phytoplankton blooms in Iberian waters have been reported. Earth Observation (EO) can provide important information about the spatial and temporal distribution and the destination of blooms, with scales not available for conventional monitoring techniques. The present work aims to take advantage of public databases (Harmful Algae Event Database (HAEDAT)) to relate ocean colour data, also publicly available, (Copernicus Marine Environmental Monitoring Service (CMEMS)) with the detection of the occurrence of harmful algal blooms (HABs). From the analysis of the HAEDAT database, it was possible to observe that in Portugal, from 1987 to 2020, there were 669 HABs events, with Diarrhetic Intoxication by Shellfish (DSP) syndrome. The images were extracted from multiple ocean colour sensors (2017–2020) for periods coinciding with DSP HABs events in recent years to identify patterns in the development of HAB toxins and to assist in coastal management. Having in account the HAB events analysed (12), was observed a weak but significant correlation between the datasets when the comparison was between the biotoxin concentration and its 14th day precedent Chlorophyll a (Chl a) concentration (rSpearman=0.15). These results show how EO data relate to regular bivalve toxin monitoring programs on the Portuguese coast and are useful for future integration in modelling tools. Other than being useful for coastal water quality assessment and management, these results also reinforce the importance of maintaining existing monitoring programs on a regular basis, especially as some types of HABs may not be easily distinguishable by EO.