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Marine Ecology Progress Series

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MEPS 382:113-128 (2009)  -  DOI:

Herbivory and community organization on a subtidal cobble bed

Robert E. Scheibling1,*, Noreen E. Kelly1,2, Bruce G. Raymond1,3

1Biology Department, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
2Present address: Centre for Marine Biodiversity, Biological Station, 531 Brandy Cove Road, St. Andrews, New Brunswick E5B 2L9, Canada
3Present address: Environment, Energy and Forestry, 11 Kent Street, PO Box 2000, Charlottetown, Prince Edward Island C1A 7N8, Canada

ABSTRACT: We examined the role of molluscan mesograzers (periwinkles Littorina littorea, limpets Testudinalia testudinalis and chitons Ischnochiton ruber) in mediating macroalgal succession after a mass mortality of sea urchins Strongylocentrotus droebachiensis in a subtidal cobble bed in Nova Scotia, Canada. Experimental exclusions of mesograzers from cobbles encrusted with smooth (Phymatolithon) or rugose (Lithothamnion) coralline algae resulted in the establishment of a variety of ephemeral filamentous algae, suggesting that these small (2 to 5 mm) but abundant herbivores are the dominant agents controlling early succession and community organization in this habitat. In removing inhibitive effects of early successional species, molluscan grazing facilitated the establishment of fleshy perennial species Fucus evanescens and Chondrus crispus, which occasionally escaped grazing at small size to attain a growth refuge on the cobbles. Algal biomass and species richness were greater on Lithothamnion than Phymatolithon, suggesting that rugose crusts provide more favourable microhabitats for recruitment or survival of various macroalgae. The distribution of mesograzers differed between coralline types, likely influencing the rate and intensity of grazing: periwinkles foraged on both types of crust, whereas limpets occurred primarily on Phymatolithon and chitons on Lithothamnion. All non-coralline algae were consumed when urchins were experimentally reintroduced to the cobble bed, returning the assemblage to the urchin barrens state.

KEY WORDS: Algal community structure · Encrusting coralline algae · Biological disturbance · Molluscan mesograzers · Rocky subtidal zone · Sea urchins · Spatial complexity · Succession

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Cite this article as: Scheibling RE, Kelly NE, Raymond BG (2009) Herbivory and community organization on a subtidal cobble bed. Mar Ecol Prog Ser 382:113-128.

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