Effects of Grazing, Canopy Cover and Substratum Type on the Abundances of Common Species of Seaweeds Inhabiting Littoral Fringe Tide Pools

Abstract

Experimental manipulations were used to differentiate the effects of i) grazing, ii) Fucus distichus canopy cover and iii) the presence of Hildenbrandia rubra on the recruitment density of F. distichus and the cover abundance of ephemeral algae. Grazers were found to have the strongest (negative) effect on the density of F. distichus juveniles. Canopy effects (negative) on juveniles were not seen until late winter. Hildenbrandia presence had no significant effect on juvenile F. distichus abundance, but there was a negative relationship between the covers of ephemeral algae and juvenile Fucus. Grazers had a weak negative effect on adult Fucus canopy, no effect on Hildenbrandia cover and an enhancing effect on ephemeral algae at the peak of their abundance. Fucus canopy inhibited ephemeral algae. The results support earlier work which showed that F. distichus juveniles are more susceptible to grazing than are adults. However, the enhancement effect of grazers on ephemeral algae contradicts most earlier reports.