GEOGRAPHICAL VARIATION IN FUCUS-VESICULOSUS MORPHOLOGY IN THE BALTIC AND NORTH SEAS

Effects of stress and disturbance on morphology, reproductive effort, size and sex ratio were studied for Fucus vesiculosus populations from the Baltic Sea at Asko and the North Sea on the west coast of Sweden at Tjarno. High morphological variation was found between Fucus popula tions, with significant differences in length and weight of individual s, thallus breadth, number of branches and receptacles and receptacle weight, not only between Baltic and North Sea populations but also bet ween populations within the same area, differing in wave exposure. Wit h increasing disturbance, individuals in both studied populations were smaller and less branched. Differences were observed in plant size, w ith longer, broader and more branched plants being found in Asko compa red with Tjarno. Fucus populations at Tjarno allocated more biomass to reproduction and had longer, heavier receptacles than at Asko. Althou gh the observed morphological changes may be partly explained by diffe rences in wave exposure and salinity between the two sites, it is not possible to rule out genetic differences between the Baltic and North Sea populations. However, it is unlikely that the variations observed within the populations and between populations from the same area are genetically determined.