Tadpole Shrimp (Branchiopoda: Notostraca: Triopsidae: Triops spp.) are Seemingly Unaffected by Chronic Exposure to Chlortetracycline at Ecologically Relevant Concentrations

Human-developed antibiotics have been found in most aquatic ecosystems. They are entering natural ecosystems by a variety of means and are almost ubiquitous in all but the most pristine and isolated watersheds. Much more attention has been paid to effects of widespread antibiotics feeding back to human populations in comparison to natural ecosystems. This study explored the direct toxicological effect of chlortetracycline (CTC) on a keystone species of temporary wetlands, the tadpole shrimp (Triops spp.). Tadpole shrimp are commonly found in western Great Plains temporary wetlands, rock pools, and artificial waterbodies. CTC was administered in a 14-day static, chronic exposure test at CTC concentrations of 0 µg/L, 0.1 µg/L, 1 µg/L, 10 µg/L, and 100 µg/L. Chronic CTC exposure seemingly had no effect on tadpole shrimp in this study. Tadpole shrimp hatched and survived at similar rates across all treatments. Additionally, there were no differences found in fecundity across all treatments. The only difference detected was a smaller average body size (approximately 45% smaller) in the 100 µg/L treatment. We then determined what would be required to make a realistically sized wetland have a CTC concentration of 100 µg/L, the maximum concentration in our study. We found that the quantities of chlortetracycline needed to create and maintain the concentrations tested in this study are quite feasible to obtain in a realistic, natural environment. While we tested for direct effects of CTC on shrimp themselves, we did not explore how CTC impacts behavior or could indirectly affect tadpole shrimp through other cohabitating organisms.