Species diversity and distribution of macroalgae associated with abalone banks along the Pacific coast of Baja California Sur (B.C.S.) between Bahía Tortugas and Bahía Magdalena were studied. Six cooperative fishing areas (C) within the official fishing zones of B. C.
S. were sampled. A total of 79 taxa was identified. Species richness by locality ranged from 12 taxa in C2–56 in the southernmost locality (C6). Diversity measures based on information theory (H′) in the assemblages ranged from 2.83–4.85 in C2 and C6, respectively. However,
a relative diversity index (J′) showed C3 to be the most homogeneous assemblage (S = 26) with a maximum value of 0.878. This reflected in part the distribution of the important (frequent) species. Phaeophytes had overall higher frequencies, while rhodophytes showed the greatest number
of taxa (58). Ten taxa had relative frequencies higher than three percent and were considered the most important taxa in the abalone habitats surveyed, mainly: Eisenia arborea, Cystoseira osmundacea, Corallina officinalis var. chilensis, Gelidium robustum and Plocamium
cartilagineum. Classification analysis based on presence–absence of species roughly distinguished two groups; the first represented by cooperatives 1–4 and the second by C5 and C6, although at low similarity (Jaccard) levels. Considering species importance in the analysis (Morisitás
index) a different classification resulted. The divergence of the groups may be due to differences in sampling dates, while the correspondence of assemblages from different dates indicates mainly sharing of important (long-lived) species (E. arborea, C. osmundacea, C. officinalis
var. chilensis). The important taxa and species richness are the factors determining latitudinal structure variation.
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