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

Josef Koch,Henner Hollert,Markus Brinkmann,Elin Lundström Belleza,Thuy T Bui,Magnus Breitholtz

doi:10.1371/journal.pone.0174384

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.

Highlights

Large amounts of man-made and naturally occurring substances continuously enter the environment, where they may cause adverse effects in living organisms
While parthenogenic cladocerans of the genus Daphnia are widely used as model organisms to evaluate the hazardous potential of chemicals toward primary consumers in their entirety [1, 2], the sexually reproducing Copepoda form another group of valuable test species
This trend was found to be significant for naupliar but not for copepodite development time which showed much higher variability at low food concentrations

Summary

Introduction

Large amounts of man-made and naturally occurring substances continuously enter the environment, where they may cause adverse effects in living organisms. Information about the potential toxicity of chemicals in the aquatic environment is commonly derived from toxicity tests using only a few aquatic species, chosen to be representative of different trophic levels in the food web. While parthenogenic cladocerans of the genus Daphnia are widely used as model organisms to evaluate the hazardous potential of chemicals toward primary consumers in their entirety [1, 2], the sexually reproducing Copepoda form another group of valuable test species. Insights into copepod reproduction dynamics in stressful environments can be helpful for understanding population-level effects of sexually reproducing crustaceans in general. The euryhaline brackish water copepod Nitocra spinipes was introduced as an aquatic testing organism in ecotoxicological studies in the 1970s [6] and has since been used extensively for the evaluation of a wide range of chemicals, effluents, sediments etc. Females can produce up to 6 or more broods with sometimes over 40 nauplii per brood [15]

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