NATURE OF THE DISTRIBUTIONAL BOUNDARY OF FUCUS-SERRATUS ON THE NORTH SHORE OF SPAIN

The distribution of Fucus serratus has a sharp boundary in northern Spain. F. serratus dominates the mid-intertidal region west of Novellana, Asturias, but is absent further east. In a short transition zone, F. serratus is abundant within patches. The causes underlying this pattern were investigated by experimental transplants of F. serratus to locations in the transition zone and outside its normal range. Plants moved outside the normal range had similar growth and reproductive rates to those transplanted to the transition zone and within the zone of abundance. F. serra tus recruited at sites outside the normal boundary, apparently from transplanted thalli. Temperature affected the growth rate of embryos of F. serratus in laboratory experiments. Though high summer temperatures may be responsible for the lack of F. serratus in the inner part of the Bay of Biscay, temperature alone cannot explain the observed limit of distribution. Other factors such as limited dispersal ability and interspecific competition with other macroalgae might also be important in setting the boundary for F. serratus in northern Spain.