Niche differences between sympatric Sargassum species in the northern Gulf of California

Abstract

Sargassum johnstonii Setchell & Gardner. S. herporhizum Setchell & Gardner, and S. sinicola Setchell & Gardner var. camouii (Dawson) Norris & Yensen display spatial separation in large and small-scale zonation patterns and habitat differences at low tide on an intertidal coquina limestonereef in the northern Gulf of California, Mexico. On a small scale within mid-intertidal pools, S.johnstonii occurs in the shallowest depths, followed by S. herporhizum and S. sinicola var. camouii at successively greater depths in the pools. On a large scale in the lower intertidal zone on emergent coquina S. johnstonii again occurs in the uppermost position in zonation, with S. herporhizum below. Inthis lower area the distribution of S. sinicola var. camouii overlaps with that of emergent S. herporhizum but most plants of the former species occur in pools. Thus, in the same low-tide habitat (pools or emergent coquina) the species occupy the different vertical zones, whereas when they do occupy the same vertical zone they occupy different habitats. At some sites where S. herporhizum and tide pools are rare or absent, S. sinicola var camouii in the intertidal zone shifts its habitat from tide pools to mostly emergent habitats