In the framework of investigations on possible effects of eutrophication on the macrophy-tobenthos in Kiel Bay (Western Baltic), a large-scale survey of the distribution and occurence of the genus Fucus was carried out in 1987/88. For large-scale quantitative mapping, underwater television was employed or direct observations from the water surface were made. Species composition and quantitative biomass data were obtained by dredging and SCUBA-diving. Comparison with the results of earlier investigations revealed a drastic decline in Fucus biomass from between 40 000 and 45 000 t wet wt down to only 2400 t wet wt in 1987/88, which means a decrease by 94 to 95 %. Whereas Fucus vesiculosus as well as F. serratus were still frequent at depths below 2 m down to 13 m in the seventies, during our investigation Fucus spp. was not found in water depths greater than 2 m. Possible causes for the observed changes are discussed, and it is concluded that decreased light levels or increased epiphyte growth as a result of eutrophication, and the reduction of substrate for algal growth due to stone fishing and sand deposition, are the main causes for the decline of Fucus spp.
