Prediction of Sporadic Mucilaginous Algal Blooms in the Northern Adriatic Sea

In the eutrophic waters of the Northern Adriatic, occasional, large scale mucilage events cause economic and ecological damage. A hypothesis linking biology, hydrography and water chemistry at the mouth of the Po River is proposed to explain the sporadic occurrence of mucilaginous algal blooms. We propose that the formation of stable mucilaginous macroaggregates associated with the blooms occurs in the following temporal sequence: low flow in the Po River leads to nutrient limitation offshore. Mucilage is produced by nutrient limited phytoplankton. Stable hydrographic conditions (which are consonant with low river flows) allow the development of mucous macroaggregates under conditions of low calcium concentration. A subsequent period of hydrographic mixing with the relatively high calcium concentrations in seawater causes stabilisation of the macroaggregates. Seawater circulation then causes the movement of stable mucilage aggregates in a southerly direction parallel to the coast or onto the beaches.