| I examined effects of native kelps, Laminaria longicruris and L. digitata, and of the invasive green alga, Codium fragile ssp. tomentosoides, on the composition, abundance and diversity of native algal and invertebrate taxa in the rocky subtidal in Cranberry Cove, Nova Scotia, Canada. I compared the effect of stands of Codium and kelp on mobile benthic macrofauna and turf algae by measuring the response of these assemblages to the experimental removal of the respective macroalgal canopy. From June 2003 to November 2004, I censused macrofauna and measured canopy cover within 4 x 10 m strips of alternating Canopy Intact (control) and Canopy Removed treatments in both a Codium- and a Laminaria-dominated habitat.; I also compared epifaunal and epiphytic algal assemblages on fronds and holdfasts of Codium and Laminaria, both for individual plants and for monospecific and mixed stands of the two canopy species.; My results indicate that selection of algal habitats by mobile macrofauna is likely determined by differences in shelter and foraging opportunities offered by each algal species. Habitat selection by epifauna is more likely determined by specific chemical, structural and morphological characteristics of the plants, rather than the amount of habitable area available for colonization. Overall Codium and Laminaria differentially affect the abundance and diversity of mobile macrofauna and epibionts, indicating that a shift in dominance from Laminaria to Codium will likely have a profound effect on the structure and function of shallow, rocky subtidal ecosystem of the Northwest Atlantic. |
