Prediction of sporadic mucilaginous algal blooms in the Northern Adriatic sea

In the eutrophic waters of the Northern Adriatic, occasional, large scale m ucilage events cause economic and ecological damage. A hypothesis linking b iology, hydrography and water chemistry at the mouth of the Po River is pro posed to explain the sporadic occurrence of mucilaginous algal blooms. We p ropose 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 nu trient limited phytoplankton, Stable hydrographic conditions (which are con sonant with low river flows) allow the development of mucous macroaggregate s under conditions of low calcium concentration. A subsequent period of hyd rographic mixing with the relatively high calcium concentrations in seawate r causes stabilisation of the macroaggregates. Seawater circulation then ca uses the movement of stable mucilage aggregates in a southerly direction pa rallel to the coast or onto the beaches. (C) 1999 Elsevier Science Ltd. All rights reserved.