The influence of three common antibiotics on coastal benthic foraminifera: implications for culture experiments and biomonitoring

Abstract. Synthetic antibiotics are medicinal substances crucial for human and animal health and welfare. Recently they have been expansively used in the food industry for reducing bacterial infections in livestock, poultry, and aquaculture. Due to their extensive use, antibiotics are increasingly accumulating in coastal marine ecosystems and cause damage to marine organisms. In this study we investigated the influence of antibiotics on benthic foraminifera, which are widespread marine protists. Foraminifera are often used as bioindicators to define the health state of coastal ecosystems. To gain deeper insights into the ecology of foraminifera and enhance their use as bioindicators, numerous studies have conducted laboratory experiments, with some employing antibiotics to prevent bacterial infections in the cultures. However, for decades it remained unresolved whether antibiotics have either a negative or a positive effect on foraminifera. In this study we tested the influence of three commonly used antibiotics (ampicillin, chloramphenicol, and tetracycline) as well as a mixture of the three on nutrient uptake of two benthic foraminifera, temperate fjord species Nonionella sp. T1 and large tropical species Heterostegina depressa. Our results showed that tetracycline present alone or in mixture has the most negative influence on the nutrition uptake of foraminifera, and under light conditions it may completely inactivate foraminiferal activity. Ampicillin showed a less negative impact, likely caused by a hydrolysis of this drug in seawater over days. Finally, chloramphenicol reduced the nutrient uptake of the symbiont-bearing H. depressa but not that of Nonionella sp. T1, which indicates that this antibiotic exerts a species-specific effect. However, given that the applied antibiotic concentrations were high following the supplier's recommendation for laboratory cultures, an extrapolation of these results to antibiotic concentrations occurring in coastal waters is difficult.