Pharmaceuticals are common chemical contaminants in estuaries receiving effluent from wastewater and
sewage treatment facilities. The purpose of this research was to examine benthic microalgal (BMA) com-
munity responses to sublethal exposures to tylosin, a common and environmentally persistent antibiotic.
Bioassays, using concentrations of 0.011–218
l
mol tylosin l
1
, were performed on intertidal muddy sed-
iments from North Inlet Estuary, SC. Exposure to tylosin resulted in a reduction in total BMA biomass and
primary productivity. Furthermore, exposure seemed to retard diatom growth while having a minimal
effect on cyanobacteria biomass. Estuarine systems receiving chronic inputs of trace concentrations of
tylosin, as well as other antibiotics, may experience significant reductions in BMA biomass and primary
productivity. Given the well-documented role of BMA in the trophodynamics of estuaries, these impacts
will likely be manifested in higher trophic levels with possible impairments of the structure and function
of these sensitive systems