The effects of chlorine-free pulp mill effluents on reproduction and grazing interactions in Baltic Sea Fucus vesiculosus L.

The effect of ClO2-bleached and chlorine-free pulp mill effluents on differ ent life stages of the brown alga Fucus vesiculosus L. from the Baltic Sea was investigated in a series of laboratory experiments. The ClO2-bleached e ffluent strongly inhibited germination already at a 5% concentration. In co ntrast, chlorine-free effluent had little effect on either fertilisation or germination in the species; a slightly negative effect on fertilisation wa s seen only at 25% concentration. It is concluded that a shift to chlorine- free bleaching improves the potential fop survival and re-establishment of F. vesiculosus in pulp mill receiving areas. One week of pre-exposure of F. vesiculosus germlings to chlorine-free pulp-mill discharge with a concentr ation of 25% did not significantly affect the palatability of the F. vesicu losus germlings to the fresh water snail Lymnaea peregra O. F. Muller. Neit her did pre exposure of adult F. vesiculosus tissue to chlorine-free efflue nts (25%) affect the grazing rate of the isopod Idotea baltica Pallas. Howe ver, when offered a choice, I. baltica significantly preferred feeding at p re-exposed F: vesiculosus sus. This indicates that the effluent indirectly can contribute to a higher grazing pressure of I. baltica in areas affected by pulp mill effluents.