Background.

A recent interest has emerged for studying benthic marine diatoms (BMD) whose environment is influenced by potentially toxic elements (PTE), mainly metals that can alter their taxocoenoses parameters and cause deformities in the diatom frustules.

Objective.

To explore which particular characteristics may represent a response by BMD to PTE in environments polluted by mining residues, using the typical structure of the diatom taxocoenoses as reference, i.e., floristics, species richness, and diversity and dominance, as well as frequency of deformed frustules.

Methods.

Rock and sediment samples were taken in May 2015 and January 2016 at Santa Rosalía, BCS, a beach contaminated by mining waste.

Results.

Between 1 and 7.6% of deformed valves per site were recorded. This frequency of deformed frustules suggests the impact of contamination by EPT in the area. Diversity values of H´ between 1.1 and 4.3 were recorded, which are within the typical intervals of diversity for uncontaminated sites, although EPT concentrations such as Cu 3760 mg kg-1, Zn 2294 mg kg-1, Ni 401 mg kg-1, Pb 216 mg kg-1, recorded in the area exceed the mid-range effect values, indicating that 50% of the biota present would be affected.

Conclusions.

The high abundance of certain diatom taxa may indicate their ability to resist or tolerate PTE, while those exhibiting deformed frustules could be considered sensitive taxa.