RESPONSE OF EPILITHIC MICROPHYTOBENTHOS OF THE WESTERN BALTIC SEA TO IN-SITU EXPERIMENTS WITH NUTRIENT ENRICHMENT

The response of epilithic microphytobenthos to in situ nutrient enrich ments was studied in the Kiel Fjord, Western Baltic Sea. For this purp ose an experimental setup with continuous nutrient supply was designed and installed. Experiments followed the colonization of artificial su bstrates and the responses of benthic algae to different concentration s and combinations of nitrogen and phosphate. They revealed nitrogen l imitation of epilithic microflora from late spring to autumn, such tha t there was higher biovolume with increasing nitrogen concentrations. Diatoms became dominant in all experiments except one in which the rho dophyte Ceramium strictum prevailed. Species composition was altered b y nutrient treatments; one to several species were highly favoured by nutrient enrichment. Consequently, diversity was negatively correlated with final yield. These findings support the hypothesis that competit ion is an important factor structuring microphytobenthic communities.