Satellite Observation of Bio-Optical Indicators Related to Dinoflagellates Blooms in Selected Mediterranean Coastal Regions

Abstract

Satellite data were used to assess phytoplankton dynamics in the Mediterranean Sea, in relation to blooming episodes of Alexandrium, the dinoflagellates genus which causes most (harmful) algal blooms in the basin. A comparison of in situ data, collected on the coast of Catalonia, Sardinia and Sicily in 2002-2003, with images recorded by the SeaWiFS albeit hampered by space/time resolution too poor to discern small features in harbours, bays or beach areas, and by other limitations suggests that the recurrence of Alexandrium is linked to local (near-coastal) factors, and only occasionally to larger mesoscale features typical of open waters. Examples are provided of the frequent decoupling between inshore and offshore blooming regimes, even in those cases when they seem to co-vary (e.g. considering inter-annual variability). Correspondences between imaged patterns and Alexandrium outbursts are seen to occur episodically, implying that the processes shaping the local (harmful) algal blooms and the regional blooms are different, or overlap only marginally. Thus, local measurements cannot be taken as representative of "larger scale" phenomena, while the satellite data might be useful to place local events into a regional contest, but not to explore the dynamics of "smaller scale" phenomena, which require direct in situ monitoring.