SIMULTANEOUS EFFECTS OF TRACE-METALS AND EXCESS NUTRIENTS ON THE ADRIATIC SEAWEED FUCUS-VIRSOIDES (DON) J AG (PHAEOPHYCEAE, FUCALES)

Simultaneous effects of trace metals (Mn, Co, Zn) and excess nutrients on the Adriatic seaweed Fucus virsoides (Don.) J. Ag. were studied un der controlled conditions. Results indicated that ambient nutrients mo dify the accumulation of Mn and Co, whereas Zn accumulation is not aff ected by the presence of nutrients. Several experimental series of dif ferent duration were carried out in succession. In the short-term expe riment, Mn accumulation was the highest in the presence of nitrate and in the absence of nutrients in the long term series. Manganese accumu lations was lowest in the presence of phosphate while Co accumulation was highest in the phosphate enriched media. The joint effects of exce ss nutrients and trace metals on growth and survival were observed in six consecutive series of different duration. Trace metals reduced gro wth in the same sequence as observed previously viz. Zn-Co-Mn. Zinc, w hich is most inhibitory, also showed the highest rate of accumulation. In the presence of nitrate and metals the growth was improved and fol lowed the same sequence as if the metals were applied singularly. Modi fications in growth expressions were obvious in all the phosphate enri ched media. Phosphate alone was inhibitory or deleterious, especially in combination with Mn. If both nutrients were applied together with t he metals, growth was improved in the presence of Mn and Co compared w ith just phosphate. Usually only short-term growth and survival was po ssible with this combination, which was lethal in the presence of Zn. A relationship between the growth expressions of the plants and the se ason in which they were collected was indicated. The elemental composi tion of the plants (C, N, P) suggests a correlation between tissue car bon and Mn accumulation, whereas in the Co and Zn samples this relatio nship was less clear. Tissue nitrogen showed small variations and incr eased both in the presence of phosphate and nitrate. Phosphorus conten t increased in the presence of phosphate and of phosphate and nitrate applied together 8 to 37 times the initial values. A high tissue phosp horus content was apparently not inhibitory for growth. In general low C/N ratios (< 10) followed necrosis of the plants.