Rapid adaptation to oil exposure in the cosmopolitan copepod Acartia tonsa

Oil spills are potential environmental hazards to marine ecosystems worldwide. Oil spills may persist in seawater longer than one generation of many zooplankton species. However, whether populations of short-lived and fast growing marine organisms adapt to oil exposure through natural selection is not known.

To test this, the cosmopolitan estuarine copepod Acartia tonsa was exposed to pyrene continuously for two generations, at the concentrations 0, acetone control, 1, 10, 100 and the saturated pyrene concentration in seawater, 100+ nM. Pyrene is one of the most toxic components in crude oil to marine copepods.

The key fitness-related traits were quantified: survival, size at maturity, grazing rate and the reproductive success. Exposure to the concentration of pyrene saturated in seawater (100+ nM) resulted in 100 % mortality before adulthood in the first generation. In the other treatments (≤ 100nM), the first generation had a higher grazing rate than the second generation.

Exposure to pyrene had no effect on the grazing rate. At the concentration of 100 nM, pyrene exposure caused reductions in survival, size at maturity of females, egg production and hatching success. The reduction in size at maturity of females was less pronounced in the second generation. Strikingly, both survival, egg production and hatching success were recovered in the second generation, indicating a rapid selection towards individuals with adaptations to deal with pyrene exposure.

Our results show that populations of short-lived and fast-growing copepods have the potential of showing surprisingly strong resilience to the type of oil contamination they might face in their natural coastal habitats