Abstract
Microplastic debris is a pervasive and widespread pollutant that poses a risk to aquatic biota and healthy marine ecosystems. Copepods are an abundant and ecologically important class of zooplankton, common to marine ecosystems across the globe. Field studies and laboratory exposures have identified that copepods readily consume microplastic particulates. In the copepod Calanus helgolandicus, prolonged exposure to polystyrene microbeads resulted in significant reductions in feeding, egg size, hatching success and survival. We hypothesise exposure to microplastics reduces feeding in copepods, resulting in energetic shortfalls for which lipids can act as a proxy. The coldwater copepod Calanus finmarchicus is a keystone species, common to the North Atlantic. During maturation, these copepods rapidly build-up their wax-ester store (oil sac); this lipid reserve is essential to the copepod’s buoyancy regulation and energetic budget when overwintering, and is of high nutritional value to predators. Following a 48-hour acclimation period, juvenile C. finmarchicus were incubated in natural seawater containing a mixed assemblage of cultured algae (control), with the addition of either nylon granules (10-30 µm) or fibres (10x30 µm) at a concentration of 100 microplastics mL-1. Algal ingestion rates and developmental stage were monitored daily, while prosome length, oil sac size and lipid profiles were assessed following the six-day experiment. No significant differences in growth, sex-ratios or oil-sac size were identified, however we observed juvenile copepods moulted into adults significantly earlier (ANOVA, P<0.05) when exposed to microplastic. We discuss the impact microplastic exposure can have on feeding and energetics of animals, in relation to the individual and marine food webs as a whole.
