Temperature and food quantity effects on the harpacticoid copepod Nitocra spinipes: Combining in vivo bioassays with population modeling

Investigating Population-Level Toxicity of the Antidepressant Citalopram in Harpacticoid Copepods Using In Vivo Methods and Bioenergetics-Based Population Modeling

Recent research has revealed various lethal and sublethal effects of the selective serotonin reuptake inhibitor citalopram hydrobromide on the harpacticoid copepod Nitocra spinipes. In the present study, an individual-based model (IBM) grounded in the dynamic energy budget (DEB) theory was developed to extrapolate said effects to the population level. Using a generic DEB-IBM as a template, the model was designed to be as simple as possible, keeping model components that are outside the scope of the core DEB theory to a minimum. To test the model, a 56-day population experiment was performed at 0, 100, and 1000 μg citalopram hydrobromide L^-1 . In the experiment, the populations quickly reached a plateau in the control and at 100 μg L^-1 , which was correctly reproduced by the model and could be explained by food limitations hindering further population growth. At 1000 μg L^-1 , a clear mismatch occurred: Whereas in the experiment the population size increased beyond the supposed (food competition-induced) capacity, the model predicted a suppression of the population size. It is assumed that the IBM still misses important components addressing population density-regulating processes. Particularly crowding effects may have played an important role in the population experiment and should be further investigated to improve the model. Overall, the current DEB IBM for N. spinipes should be seen as a promising starting point for bioenergetics-based copepod population modeling, which-with further improvements-may become a valuable individual-to-population extrapolation tool in the future. Environ Toxicol Chem 2023;42:1094-1108. © 2023 SETAC.

Making Sense of Life-History Effects of the Antidepressant Citalopram in the Copepod Nitocra spinipes Using a Bioenergetics Model

The global consumption of human antidepressants has steadily increased over the last years. The most widely prescribed antidepressants are the selective serotonin reuptake inhibitors (SSRIs), which have been linked to various life-history effects in nontarget organisms. We investigated the effects of the SSRI citalopram hydrobromide on the life history of the copepod Nitocra spinipes. Slight but significant developmental delay effects were observed at nominal concentrations of 0.1 and 1 µg/L, with stronger effects occurring at measured concentrations of 178 µg/L and above. At 77 µg/L and above, a significant increase in adult body length and offspring production/brood was found, although the time between brood releases remained unaffected. The pre-adult surviving fraction was significantly reduced (by 44%) at 765 µg/L. For a mechanistic evaluation of these observations, we used a bioenergetics model for N. spinipes based on the dynamic energy budget theory. Toxicokinetic and toxicodynamic submodels were used to dynamically simulate the chemical uptake and elimination, as well as dose-response relationships for hypothetical physiological modes of action and survival over time. Although none of the commonly invoked physiological modes of action, acting on assimilation, maintenance, growth, or offspring production, could explain the observed combination of effects, a newly proposed physiological mode of action acting on the process of maturation delivered correct predictions in terms of each effect's direction. The model fits could be further improved by allowing for a gentler concentration-effect slope and by adding an auxiliary physiological mode of action acting on the reproduction efficiency. The quantitative explanations provided in the present study offer a starting point for exploratory simulation studies investigating the effects of SSRIs at higher ecological levels. Environ Toxicol Chem 2021;40:1928-1939. © 2021 SETAC.

Climate change and oil pollution: A dangerous cocktail for tropical zooplankton

Climate change and oil pollution pose a major threat to tropical marine ecosystems and to the coastal communities relying on their resources. The Gulf of Guinea is severely affected by multiple human induced stressors, but the potential impacts of these on marine productivity remain unknown. We investigated the combined effects of heatwaves (climate stressor) and the polycyclic aromatic hydrocarbon pyrene (proxy for oil) on the copepod Centropages velificatus. We quantified survival, reproduction and fecal pellet production of females exposed to concentrations of 0, 10, 100 and 100+ nM (saturated) pyrene under simulated heatwaves of different thermal intensity (+3 °C and +5 °C above control treatment temperature). Thermal stress due to both moderate and intensive heatwaves resulted in reduced survival and egg production. The negative effects of pyrene were only measurable at the high pyrene concentrations. However, thermal stress increased the sensitivity of C. velificatus to pyrene, indicating a synergistic interaction between the two stressors. We document that the interaction of multiple stressors can result in cumulative impacts that are stronger than expected based on single stressor studies. Further research is urgently needed to evaluate the combined impact of climatic and anthropogenic stressors on the productivity of coastal ecosystems, particularly in the tropical areas.