Substratum-specific facilitation of recruitment in the intertidal kelp Hedophyllum sessile: Topographical complexity and mediation by adult canopy cover.
Boizard, Sophie*,1, De Wreede, Robert1, 1 University of British Columbia, Vancouver, BC, Canada
ABSTRACT- In marine benthic communities, substratum complexity is an important factor regulating recruitment and subsequent patterns of distribution and abundance. Increased surface area available for attachment and increased moisture retention associated with high substratum complexity, for example, may be particularly important in intertidal habitats. Rocky low intertidal communities on the west coast of Vancouver Island are dominated by the canopy-forming kelp, Hedophyllum sessile. We examined whether H. sessile recruitment is facilitated by substratum complexity and how this interaction may be mediated by adult canopy cover and wave exposure. Juvenile occurrence on naturally occurring substrata was compared under natural canopy cover and artificially reduced canopy in permanent quadrats at a wave exposed and a wave sheltered site. Articulated coralline algae and holdfasts of adult H. sessile were the two most common topographically complex substrata found at our sites, while encrusting algae and bare rock were the least complex. H. sessile juveniles did not recruit randomly among the various substrata available at our sites. In the presence of a natural canopy, at both the wave sheltered and wave exposed site, relative to substratum availability, articulated corallines bore disproportionately more, and other substrata bore disproportionately fewer, juveniles. However, when adult canopy was reduced, a disproportionate number of juveniles recruited onto the holdfasts of adult H. sessile. While articulated corallines continued to facilitate recruitment under these conditions, it did less so than in the presence of a natural canopy. Encrusting algae and bare rock consistently inhibited recruitment regardless of wave exposure or canopy cover. Our results indicate that substratum complexity plays a significant role in facilitating H. sessile recruitment. However, in this community the capacity of a topographically complex substratum to facilitate recruitment depends largely on the extent of canopy cover. Mechanisms by which canopy cover may mediate substratum-specific recruitment processes may therefore hold significant implications for population persistence and successful recruitment, especially following periods of high disturbance.
Key words: recruitment, substratum complexity, canopy cover, Hedophyllum sessile
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