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Hemichordates as a model system for investigating intertidal zonation in soft sediments
Schrage, Kharis R
Schrage, Kharis R
Abstract
Intertidal zonation of organisms is well studied on rocky shores but less so in soft sediment communities. On rocky shores, biotic factors such as predation often set the lower bound of a zone, while abiotic factors set the upper bound. Here I describe the zonation of hemichordate worms at two field sites in Maine and Virginia. In Virginia, Saccoglossus kowalevskii occurs in the mid-intertidal zone at densities up to 500 m-2. In Maine, two hemichordate species, Saccoglossus bromophenolosus and Protoglossus graveolens, co-occur at densities approaching 100 m-2. Hemichordates have chemical defenses that appear to deter fish, but not crustacean, predators. Six species of crustaceans and two species of predatory polychaetes were fed all three species of hemichordate. Crustaceans readily consumed hemichordates, while the polychaetes did not. In predator choice experiments, hermit crabs preferred hemichordates over the tissue of blue mussels, while green crabs preferred mussel tissue. These results suggest that, consistent with the rocky intertidal paradigm, the lower bound of the hemichordate zone could be set by crustacean predators, at least some of which appear to prefer hemichordates over palatable alternatives.
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2017-05-01
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Biology