High species diversity (H') of benthic diatoms in a coastal lagoon located within a natural protected area

Background. The structure of benthic diatom assemblages (diversity, equitability, dominance) may be useful in assessing their ecological status in natural protected areas. Goals. To describe the structure of epipelic diatom assemblages from Laguna Guerrero Negro (LGN), a protected coastal lagoon, and test the hypothesis that H'diversity values would be higher for diatom assemblages in LGN sediments than in typical benthic diatom assemblages. Methods. Sediment samples were collected in the lagoon on November 2013, and January, March, and July 2014. Diatoms were mounted on permanent slides and examined at 1000× using phase contrast microscopy. In each slide, 500 valves were counted to compute relative abundances of each taxon, and species diversity, equitability, and dominance, using Shannon (H'), Pielou (J'), and Simpson (λ) indices, respectively. Likewise, similarity between samples was measured. The calculated median value of H' from LGN was compared to previously recorded median values to test the hypothesis that significant differences exist. Results. A total 225 diatom taxa were counted. With few exceptions, the similarity between samples was <60%. Relative abundances depict typical benthic diatom assemblages, with an average H'= 4.96 bits/taxon, and corresponding values of equitability and dominance. The median value of H' (Md = 4.9) was significantly higher than the median value (Md = 3.7) found in previous studies. Conclusions. The structure of the epipelic diatom assemblages from LGN and their patchy distribution are similar to that of typical diatom assemblages, but with unusually high values of H' that lead us to reject the statistical null hypothesis and thus sustain our research hypothesis.