EFFECT OF ROCKY INTERTIDAL AMPHIPODS ON ALGAL RECRUITMENT: A FIELD STUDY<sup>1</sup>

ABSTRACTEvidence about the potential of mobile marine invertebrates to act as algal spore dispersal agents is presently circumstantial. Using a field correlational and experimental protocol, our study tested the hypothesis that amphipods can increase the spore recruitment of the red algaIridaea laminarioidesBory.Iridaea laminarioidesspore recruitment onto glass slides was measured at a site with high amphipod abundance and a site with low density of amphipods. To evaluate the effect of anUlvacanopy on recruitment, replicated glass slides with and without a surroundingUlvacanopy were installed at both sites. The number ofI. laminarioidesspores recruited on the glass slides was four to eight times higher at the high amphipod abundance site than at the low density site. However, the presence of anUlvacanopy covering the glass slides did not significantly increase the recruitment ofI. laminarioides.Because the abundance ofI. laminarioides, the proportion of cystocarpic plants, and the percentage of open cystocarps only differed slightly between the low and high abundance amphipod sites, we suggest that the variation in recruitment between the sites is due to the differences in amphipod abundance (and their movements) and not to differences in spore production. Moreover, the presence ofI. laminarioidescystocarps showing amphipod grazing scars was significantly higher at the high amphipod density site than at the low density site.

Kimelfe