Rhodolith Bed Composition in the Southwestern Gulf of California, Mexico

Abstract

The composition of rhodolith beds, relative abundance of species and growth-forms, was evaluated in relation to a depth gradient and substratum along the southwestern Gulf of California. Replicate transects were established in twelve rhodolith beds to evaluate the species and growth form distribution in relation to depth (2-7, 7-12 and 12-20 m) and habitat (sand vs. rock). Four species with four growth-forms were determined: Lithophyllum margaritae which ranged in growth-form from fruticose, fructifoliose to foliose; Lithothamnion muelleri where the growthform range was lumpy to fruticose; in both Neogoniolithon trichotomum and Mesophyllum engelhartii where only fruticose growth-form was observed. Lithophyllum margaritae was the most abundant species in relation to depth in the sandy habitat and Lithothamnion muelleri was dominant in the shallow rocky areas. The presence of N. trichotomum was limited to shallow sandy beds and M. engelhartii was limited to the deeper areas. Growth-forms also showed a variation with depth and substrata, in where fruticose forms dominate in sandy areas, lumpy forms dominate in rocky habitats and foliose forms were more abundant in the deeper areas. The differences in the abundance of each species and growth form might be explained by a combination of biological features; growth rate, density of reproductive structures and calcification rate in relation to environmental features such substrate type (rock vs. sand), water motion and light.