MEPS 271:121-132 (2004)  -  doi:10.3354/meps271121

ABSTRACT: We examined the invertebrate assemblages associated with macroalgal canopies in the Mingan Islands (northern Gulf of St. Lawrence, eastern Canada) in the summer and fall of 2001. Invertebrates were sampled in patches or beds of 4 species of macroalgae (Alaria esculenta, Agarum cribrosum, Desmarestia viridis and Ptilota serrata) as well as in adjacent urchin barrens. Multivariate analyses of the invertebrates on the algal fronds, those on the underlying substratum, and the 2 groups together demonstrated differences in invertebrate assemblages among all 5 habitats. A. esculenta sheltered the most distinct invertebrate community due to the domination of the substratum under this alga by the blue mussel Mytilus edulis. Differences among other canopy types were due to differences in invertebrate assemblages both on the algal fronds and on the substratum. A manipulative experiment involving the removal of the canopy of the 2 most abundant macroalgae, A. esculenta and A. cribrosum, was carried out to examine their effects on mussels. Recruitment of mussels onto ceramic tiles varied among treatments and was greatest in the A. esculenta zone with greater, but non-significant, recruitment under the canopy. The growth of mussels from early July to October was higher in the A. cribrosum zone than the A. esculenta zone. However, there was no effect of the algal canopy in either zone. Our study demonstrates that the local diversity and distribution of benthic invertebrates is intimately associated with macroalgae, and reinforces the need for detailed sampling and analyses for assessing distributional patterns.

KEY WORDS: Biodiversity · Community structure · Ecosystem engineering · Kelp bed · Mytilus edulis · Positive interactions