The influence of season and barnacles on the algal colonization of patella vulgata exclusion areas

Abstract

Patella vulgata were excluded from barnacle dominated areas at Port St Mary, Isle of Man by wire fences attached to the rock in September 1977, December 1977, April 1978 and July 1978. The sequences of algal colonization of these exclusion areas differed markedly with season: in autumn diatoms were followed directly by Fucus, in winter and spring diatoms were followed by green algae and then Fucus, and in late summer Fucus sporelings arose directly on the barnacles. There was no evidence that the initial stages were necessary for the subsequent recruitment of Fucus. Semibalanus (= Balanus) balanoides was scraped from half of the exclusion areas (with suitable controls) of a second series of experiments set up in October 1978, February 1979, April 1979. The pattern of algal colonization was very different in the scraped and unscraped halves of the exclusion areas. In the October experiment Fucus rapidly recruited directly on the barnacles, in contrast diatoms, green algae and a little Fucus recruited very slowly to the scraped half. In February and April Ulothrix directly colonized the scraped area, and was followed by Blidingia. Blidingia was directly recruited to the unscraped half. Diatoms were not so prevalent on the second set of experiments. There was minimal algal growth in the controls of both sets of experiments. © 1981, Marine Biological Association of the United Kingdom. All rights reserved.