Temperature and food quantity effects on the harpacticoid copepod Nitocra spinipes

Copepods play a fundamental role in the food chain of our oceans as they feed on algae and get eaten by fish. Amongst others, the harpacticoid copepod species Nitocra spinipes has become a popular model species in aquatic toxicity testing over the past few decades. To understand the combined effects of chemical pollution and climate change-related stressors on copepod populations, a proper quantification of those processes is essential. In this study, GhEnToxLab researcher Josef Koch and his Swedish coauthors (Stockholm University) quantified the effects of temperature and food shortage as two climate change-related environmental stressors on Nitocra spinipes and implemented the corresponding stress functions into an individual-based population model for this species. Especially high temperatures and low food concentrations were found to strongly reduce the reproductive output of N. spinipes and thus are likely to have negative implications on the population level.


Scientific abstract

The harpacticoid copepod Nitocra spinipes has become a popular model species for toxicity testing over the past few decades. However, the combined influence of temperature and food shortage, two climate change-related stressors, has never been assessed in this species. Consequently, effects of three temperatures (15, 20 and 25°C) and six food regimes (between 0 and 5 × 105 algal cells/mL) on the life cycle of N. spinipes were examined in this study. Similarly to other copepod species, development times and brood sizes decreased with rising temperatures. Mortality was lowest in the 20°C temperature setup, indicating a close-by temperature optimum for this species. Decreasing food concentrations led to increased development times, higher mortality and a reduction in brood size. A sex ratio shift toward more females per male was observed for increasing temperatures, while no significant relationship with food concentration was found. Temperature and food functions for each endpoint were integrated into an existing individual-based population model for N. spinipes which in the future may serve as an extrapolation tool in environmental risk assessment. The model was able to accurately reproduce the experimental data in subsequent verification simulations. We suggest that temperature, food shortage, and potentially other climate change-related stressors should be considered in environmental risk assessment of chemicals to account for non-optimal exposure conditions that may occur in the field. Furthermore, we advocate combining in vivo bioassays with population modeling as a cost effective higher tier approach to assess such considerations.

Full reference (link)

Koch J, Bui TT, Lundström E, Brinkmann M, Hollert H, Breithotz M. Temperature and food quantity effects on the harpacticoid copepod Nitocra spinipes: Combining in vivo bioassays with population modeling. Plos one 12 (3). Accepted Article