CHANGES AND DEGRADATION OF SEAWEED STANDS IN THE NORTHERN ADRIATIC

During the last two decades conditions in the polluted shelf area of t he Northern Adriatic became critical, leading to eutrophication and an oxia. They are reflected in changes and degradation of the macrophytob enthos with simultaneous increase of phytoplankton blooms. Pollution-i nduced changes of the benthic algal vegetation comprise altered zonati on patterns and leading algal associations along with a decrease in sp ecies number and fresh weight biomass. A reduction or absence of fucoi d stands was observed in the eulittoral and sublittoral. Fucus virsoid es was in most cases replaced by ephemeral species which form distinct zones during spring and by turf-like mats of Gelidium pusillum. Subli ttoral Cystoseira stands were either reduced or absent, replaced by po pulations of Halopteris scoparta, Dictyota dichotoma, Halopithys incur vus, Padina pavonica and under extreme conditions by Ulva rigida with Scytosiphon lomentaria and Enteromorpha species during spring. A decre ased depth penetration of macroalgae was observed in polluted sites. I t seems likely that amorphous mucus aggregations resulting probably fr om excess phytoplankton blooms which were found during summer months o f the last few years, have a deleterious effect on macroalgae.