Effects of osmotic stress on gamete size, rhizoid initiation and germlinggrowth in fucoid algae

Abstract

Effects of osmotic stress on gamete size were studied for Fucus vesiculosus; spermatozoids behaved as osmometers when the osmotic pressure of the external artificial seawater medium (ASP12S) was changed. The non-osmotic volume was approximately 44% of the spermato- zoid volume in full-strength ASP12S. Unfertilized eggs behaved as osmometers but with a relatively small change in volume. The apparent non-osmotic volume of the egg was approximately 93% of the volume in full-strength ASP12S. The significance of these observations and their possible implications for fertilization and cross-fertilization in situ is discussed.Rhizoid initiation in zygotes of Fucus spiralis and F. vesiculosus decreased with increasing salinity. A decrease also occurred when F. vesiculosus was incubated in low salinity media, though this was not the case in F. spiralis. Subsequent growth patterns of the germlings of both fucoid algae were similar, although F. vesiculosus had a higher growth rate than F. spiralis. Both species showed a substantial decrease in growth in hyper-saline media with a smaller reduction in hypo-saline media. However, developmental abnormalities occurred in high and low salinities. It is possible that prolonged exposure to osmotic stress may disrupt the growth of fucoid algae, due to effects on the processes involved in turgor pressure regulation. © 1990 The British Phycological Society.