Control of the intertidal distribution of Gastroclonium coulteri in monterey bay, California, USA

Abstract

Transplantation and selective removal experiments were carried out on Gastroclonium coulteri (Harvey) Kylin at Mussel Point, California, USA, between June, 1975 and May, 1979. Transplanted G. coulteri survived higher in the intetidal than the natural population, except during March and April when extreme low tides, and resultant severe desiccation, occurred during the daytime. Transplants survived, but did not grow, in low intertidal tidepools. Transplants to the shallow subtidal survived and increased in overall length. Transplants to the deeper subtidal zone died within 1 month. Transplants from the subtidal to the intertidal survived, but decreased in size. At the upper boundary of G. coulteri, removal of Gigartina papillata and Rhodoglossum affine resulted in a decrease in the percent cover of Gastroclonium coulteri. Presence of the other algae thus had a beneficial rather than competitive effect on G. coulteri. Removal of G. coulteri resulted in an increase in the percent cover of G. papillata and R. affine, demonstrating that the lower boundary of these two species is set by competition with G. coulteri. At the lower boundary of Gastroclonium coulteri, removal of Phyllospadix spp. or Prionitis lanceolata led to an increase in percent cover of G. coulteri. Removal of G. coulteri did not lead to an increase in percent cover of Phyllospadix spp. Thus, the lower boundary of G. coulteri is set by competition with Phyllospadix spp. or Prionitis lanceolata, but the upper boundary of Phyllospadix spp. is not set by competition with G. coulteri. The results support the hypothesis that upper boundaries tend to be set by physical factors (here, exposure at low tide), and lower boundaries tend to be set by biological factors (here, competition).