The Role Of Copepods In The Distribution Of Hydrocarbons: An Experimental Approach

Abstract

Copepods may provide a significant pathway for the concentration and transfer of polyaromatic compounds (PAC) to higher trophic level consumers. PAC dissolved from weathered crude oil are more persistent in the environment and have much higher toxicity than the lighter, more volatile fractions of crude oil. Because of their polarity, PAC tend to accumulate in bio-lipids. Subarctic copepod species can contain up to 80% of their body dry weight in lipids and have a high surface area to volume ratio. Thus, PAC accumulation is rapid and bioaccumulation factors are in the order of 500--8000, depending upon species and lipid content. While direct toxic effects of oil on copepods have been reported in the order of 10 mg/L, toxicity increases substantially in the presence of natural ultraviolet (UV) radiation. Phototoxic effects to the copepods Calanus marshallae and Metridia okhotensis were observed at concentrations of ~2mug/L total dissolved PAC followed by 4--8 hours of exposure to ambient daylight. Responses included mortality, immobilization and discoloration of lipid sacs. Further experiments were conducted to test the interaction effects of various concentrations of PAC dissolved from weathered Alaska North Slope crude oil and subsequent exposure to sunlight with and without the UVB component to the copepods Neocalanus flemingeri and N. plumchrus. Phototoxicity was found to be a linear function of the product of light intensity and PAC concentration. High natural variability in egg production rates precluded significant results of the toxicity of oil to copepod reproduction. This work has shown that copepods could potentially provide a mechanism for the concentration of dissolved PAC from the water and its transfer into pelagic and benthic food chains.