Fysiske faktorers betydning for udbredelsen af Fucus vesiculosus og Fucus radicans i Bottenhavet

摘要

The two species Fucus vesiculosus and Fucus radicans coexist in the Bothnian Sea, a part of the northern Baltic Sea. F. radicans is recently described and is assumed to be endemic to this area. The spatial extent of the Baltic Sea have major influence on the physical conditions. The only connection to other marine areas is through the narrow danish straits, Oresund, Great Belt and Little Belt. Because of a reduced exchange of water, together with a significant freshwater inflow, the Baltic Sea is often considered the worlds largest brackish body of water. Water exchange, freshwater inflow and circulation causes north-south gradients of both salinity and temperature. The large scale distribution of F. radicans indicate that this species can tolerate lower levels of salinity than F. vesiculosus. Growth of F. vesiculosus and two common clones of F. radicans at different salinity and temperature, was investigated using a split plot design. The growth of the two species differed significantly at different levels of both salinity and temperature. Growth rate of F. radicans was significantly higher at 3 psu than at 6 and 12 psu, and significantly higher at 20° C than at 15° C. F. vesiculosus showed a significantly higher growth rate at 12 psu, but showed no difference in growth rate at the two investigated temperatures. Based on collected model data, local variations in salinity, temperature, wave exposure and slope was analyzed and compared with earlier investigations of distribution of F. radicans and F. vesiculosus on 16 locations along the coast of the Bothnian Sea. Results of this analysis indicate that local salinity affect the relative abundance of F. vesiculosus and F. radicans. Overall, the distribution data are scarce and more investigations, especially on local distribution, are needed to improve this kind of analysis.