Consequences on microphytobenthos biodiversity on microbial mats used for metal removal in
industrial effluent

Microphytobenthos, primarily composed of diatoms and cyanobacteria, are vital phototrophic
communities in estuarine intertidal zones. Changes in their composition and photosynthetic pigment concentrations can be caused by environmental stressors like metal contamination. The aim of this study was to evaluate the effects of exposure to an industrial effluent containing metals (Li, Ti, Zn) on the microphytobenthic community in estuarine microbial mats. The effluent is composed of water from different processes at the petrochemical center on the estuary coast. Microbial mat samples were collected from the Bahía Blanca estuary, Argentina and exposed to industrial effluent (n=3) and seawater (n=1). The experiment was conducted outdoors for 36 days during the winter. Subsamples were collected from microbial mats at 24 h, 72 h, 120 h, 168 h and 864 h for the qualitative identification using optical microscopy and pigment quantification via 90 % acetone extraction followed by a reading on UV-Vis spectroscopy. Results indicated a predominance of pennate diatoms in both effluent exposed and seawater mats including Entomoneis sp., Navicula grevillei, Navicula sp., Nitzschia clausii, Nitzschia longissima, Nitzschia sp. and Pleurosigma sp. members, which exhibited higher resistance than cyanobacteria (Phormidium sp., Pseudanabaena sp., Spirulina subsalsa and Spirulina sp.). Although cyanobacteria taxa were not detected in effluent-exposed microbial mats by day 7, chlorophyll a and pheopigments showed no statistically significant differences between field values and those at the end of the experiment. However, a decrease in pigments was graphically recorded between day 3 and day 5, likely attributable to ice formation on the surface of the effluent during that winter period. New bioassays are needed to consolidate knowledge about the effects of contaminated effluent exposure on microphytobenthic communities in microbial mats.