Environmental factors triggering the late-winter diatom bloom in the North Adriatic Sea

A late-winter diatom bloom (Skeletonema costatum) typically occurs in the NW Adriatic Sea, triggered by nutrient inputs from the Po River and by increasing irradiance and temperature. In 2002, the onset of the bloom was delayed with respect to previous years, due to light limitation caused by cloud coverage in the form of fog. Therefore, phytoplankton could not efficiently use the available (and abundant) nutrients originating from the river out?ow until the weather conditions and the total amount of irradiance improved to the point of triggering cell growth. In fact, when at the end of February an increased rainfall boosted Po river discharge, dissolved nutrients became available in significant amount, but irradiance was still low due to the fog. Only in March, mutated climatic conditions allowed sufficient light availability, which, coupled with available nutrients, triggered the S. costatumbloom. The temporal dynamics of bloom initiation may be fundamental in determining species composition, which, in turn, has been shown to have a strong impact on consumers recruitment.