Non-overlapping distributions of spionid polychaetes: The relative importance of habitat and competition

Abstract

The spionid polychaetes, Pygospio elegans Claparède, Pseudopolydora kempi (Southern), and Rhynchospio arenincola Hartman are found in False Bay, Washington. Two species, Pygospio elegans and Pseudopolydora kempi, co-occur in the high intertidal zone. The third species Rhynchospio arenincola occurs only in low intertidal areas. Reciprocal transplant experiments were used to test the importance of intraspecific density, interspecific density, and habitat on the survivorship of experimental animals. For all three species, only habitat had a significant effect. Individuals of each species survived better in experimental containers in their native habitat, regardless of the heterospecific and conspecific densities used in the experiments. The physical stresses associated with the prolonged exposure of the high intertidal site are experimentally shown to result in Rhynchospio mortality. From these experiments, habitat type is the only significant factor tested which can explain the observed distributions; the presence of confamilials has no detected effect on the survivorship of any species, suggesting that competition does not serve to maintain the patterns of distribution.