Variations in the structure of epiphytic diatom assemblages in subtropical macroalgae

Epiphytic diatom samples of various macroalgae from a subtropical bed taxa were analyzed in order to determine if they belonged to a single assemblage, and whether they exhibited time variations. The analysis was based on community structure, i.e. relative abundances, biological value (BVI), species diversity, dominance, and equitability. The macroalgae hosts were collected from a bed located in a beach known as El Caimancito, B. C. S. Five macroalgae taxa were chosen: Laurencia pacifica, L. johnstonii, Padina mexicana, P. caulescens and Hydroclathrus clathratus. The most abundant diatom taxa, out of 211 species were Cocconeis disculus and C. dirupta. However, according to the BVI the taxa determining the assemblage structure were Navicula incerta, Nitzschia frustulum, C. disculus and N. frustulum var. perminuta. Diversity (H') values of the epiphytic diatom assemblages varied according to macroalgae host. The highest diversity value was for P. mexicana (H' = 5), whilst the lowest value (H' = 1.48) was for L. pacifica. The estimated species diversity and richness are among the highest measured for epiphytic diatom assemblages. Time variations in the diatom assemblages of the whole macroalgae bed followed the seasonal variation proposed for Bahia de La Paz.