ABSTRACT
In South African kelp beds two filter feeding sea cucumbers, Pentacta doliolum (Pallas) and Thyone auriata (Q. & G.) form dense patches in which a consistent vertical stratification is apparent. A bottom layer of T. auriata is covered by a dense layer of P. doliolum, so that the former species seems inhibited in maintaining its standard metabolism. The apparent competition for space on the one side, the frequency of the observation of this phenomenon on the other side, and the fact that these patches remain stationary over several years led to the hypothesis that competitive exclusion does not take place, and that this coexistence may be advantageous for one or both species. Differences in morphological and bioenergetic features permit the definition of niche dimensions, enabling the two species to live in close association. The advantage of the association and its zonation pattern is discussed in view of patch stability within the kelp bed ecosystem.
