Exploring the status of motility, lipid bodies, deformities and size reduction in periphytic diatom community from chronically metal (Cu, Zn) polluted waterbodies as a biomonitoring tool.

Taxonomic metrics of diatoms are regularly used for aquatic biomonitoring, including testing for heavy metal stress. In contrast, non-taxonomical parameters in diatoms are rarely assessed. In the present study, taxonomical features of diatoms, such as cell density, chlorophyll a, species richness, and the Shannon index, were reduced at severely polluted (Cu, Zn) sites compared with less polluted sites. Some non-taxonomic parameters, such as, lipid bodies (LBs) number and size, carotenoid/chlorophyll a ratios, and frustule deformities were elevated at the severely polluted sites in comparison to the less polluted sites in both the areas. Cell size diminished and motility changed from smooth to erratic with increasing Cu and Zn pollution. Some of these behavioral and physiological changes were easily assessed (e.g., motility and formation of LBs), while morphological alterations (cell wall deformities and changes in cell size) requires more time and human expertise in diatom taxonomy. These parameters were consistent across metal concentrations of sediments, in the water, and in cells. The results illustrate the usefulness of these non-taxonomic parameters in biomonitoring, especially as early warning tools for ecotoxicity assessment and testing for sublethal effects. Some of these parameters, such as cell size and cell wall deformities, can be easily incorporated into traditional protocols, although LBs and motility metrics will require more effort.