Does fluctuating salinity induce branching of Fucus vesiculosus?

Abstract

During the field surveys in the Bothnian Sea, i.e. towards low salinity areas (approx. 4%), present authors observed that the frequency of irregularly branched Fucus vesiculosus plants increased. Salinity is known to decrease gradually towards the northern parts of the Baltic Sea. However, salinity is not steady but may fluctuate greatly on an annual and even a daily scale, and salinity can drop to zero for short periods. In order to demonstrate whether the fluctuating salinity induces irregular branching of F vesiculosusus, a experiment was carried out in the Tvärminne archipelago, on the south coast of Finland in May-September 1997. First, plants were collected and then put into two containers both of which had a fresh water and a sea water flow throught. After 48 h of treatment, the plants were removed to the same place where they had been orginally collected. After the growing season, the plants were collected again, and the number of irregularly and normally branched tips were measured. The results shows that plants with the fresh water treatment have branched irregularly. In constrast, the control plants had only a few irregularly branched tips. This experiment brings us to conclude that low salinity during the critical growing season induces irregular branching.