Changes and degradation of seaweed stands in the Northern Adriatic

During the last two decades conditions in the polluted shelf area of the Northern Adriatic became critical, leading to eutrophication and anoxia. They are reflected in changes and degradation of the macrophytobenthos with simultaneous increase of phytoplankton blooms. Pollution-induced changes of the benthic algal vegetation comprise altered zonation patterns and leading algal associations along with a decrease in species number and fresh weight biomass. A reduction or absence of fucoid stands was observed in the eulittoral and sublittoral. Fucus virsoides was in most cases replaced by ephemeral species which form distinct zones during spring and by turf-like mats of Gelidium pusillum.Sublittoral Cystoseira stands were either reduced or absent, replaced by populations of Halopteris scoparta, Dictyota dichotoma, Halopithys incurvus, Padina pavonica and under extreme conditions by Ulva rigida with Scytosiphon lomentaria and Enteromorpha species during spring. A decreased depth penetration of macroalgae was observed in polluted sites. It seems likely that amorphous mucus aggregations resulting probably from excess phytoplankton blooms which were found during summer months of the last few years, have a deleterious effect on macroalgae.