Changes in the structure of a New England (USA) kelp bed: the effects of an introduced species?

Abstract

Since its first observation in the Gulf of Maine (Northwest Atlantic) in 1987, the epiphytic bryozoan Membranipora membranacea has become the dominant epiphyte on laminarian kelps. This note describes changes in the structure of a kelp bed at Cape Neddick (Maine) after the coincident increase of M. membranacea. Percent cover, length and density of kelps decreased significantly during 1989 through 1991. The dispersion of Laminaria spp. within the kelp bed was clumped in each sampling date at a large spatial scale (meters), while the distribution of Laminaria spp. changed from a random pattern to a clumped distribution on a smaller spatial scale (0.25m2). There were no consistent differences in storm intensity between years; densities of herbivores within the kelp bed were low and also have not changed between years. Coverage of M. membranacea on laminarian kelps increased 3-fold from 1989 to 1990, and the total coverage of other epiphytes decreased. Presence of M. membranacea on kelps has contributed to the defoliation of the kelp bed at Cape Neddick. This may have important consequences to organisms that utilize kelps as habitat and shelter. -from Authors