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Survival strategies in Polysiphonia adamsiae and P. strictissima (Rhodophyta, Rhodomelaceae) subjected to sediment deposition and grazing pressure

Abstract Adaptive strategies of Polysiphonia adamsiae and P. strictissima living in conditions subject to sand deposition and amphipod grazing were investigated by in situ field observations and experimental culture in southern New Zealand between September 2001 and July 2003. The findings from this study showed that for both species, branches regenerated from prostrate axes and fragments grew 7 to 10 times faster than sporelings under the same culture conditions. Also, prostrate axes exhibited extensive creeping growth and produced dense upright branches. In contrast, sporelings exclusively grew upright until they reached c. 1–2 cm. These findings indicate that vegetative propagules have a much higher probability of forming algal turf than sporelings. In addition, prostrate axes survived darkness longer than sporelings, implying that algal thalli might be protected from amphipod grazing by sediments. This study shows that vegetative modes of reproduction predominated over sporic modes in both species. Vegetative reproduction might be advantageous for thalli to survive amphipod grazing under turf‐trapped sand.