Measurements of relative growth rates (RGR) of germlings of three species of Fucus (Fucales, Phaeophyceae) collected in Helgoland (North Sea, Germany) were carried out in the laboratory in order to determine the effects of different ultraviolet radiation (UVR, λ = 280–400 nm) conditions, UVR doses and temperatures. High ultraviolet-B radiation (UVBR, λ = 280–315 nm) levels and low temperature, as independent factors, led to a species-specific reduction in RGR which appears to be related to the vertical distribution of the species in the intertidal zone. The inhibition of RGR ranged from 10% to even death of the germling. For the most sensitive species, high temperature in combination with a high dose of UVBR caused the death of the germlings, whereas at low tem- perature germlings were able to survive. This suggest growth-related temperature dependence of sensitivity to UVBR.

Introduction

Stratospheric ozone depletion, which is now a problem not only in the Antarctic at- mosphere (Chubachi, 1985) but also in the Northern Hemisphere (Pearce, 1996), causes an increase of ultraviolet-B radiation (UVBR) reaching the earth’s surface (Seckmeyer and McKenzie, 1992). Effort has recently focused on understanding the role of current ultraviole radiation (UVR) on marine primary producers, with studies on macroalgae concentrated on effects on photosynthesis, photosynthetic pigment concentrations, growth and DNA (Dring et al., 1996a,b; Altamirano et al., 2000a,b; Wiencke et al., 2000).

A principal feature of intertidal macroalgal vegetation on rocky shores is readily apparent: distinct bands of particular species or associations run parallel to the shoreline. It has been supposed that this distribution pattern reflects the capacity to withstand the physiological stresses associated with emersion at the upper limits (Lüning, 1990). Significantly, it has recently been demonstrated that the upper limits of the zonation patterns of large sublittoral kelps (Laminaria, Alaria, Saccorhiza and Phyllariopsis) from the Arctic and the Straits of Gibraltar are correlated with underwater UVR levels that could affect the survival of the single- and few-celled stages of their life histories (Wiencke et al., 2000). As UVR daily doses in the intertidal system are much higher than in the sublittoral zone, the possible rela- tionship between UVR tolerance and vertical distribution of intertidal macroalgae remains as an important matter to be investigated.

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