Lethal and sublethal effects of a molybdenum mine tailing on marine zooplankton: Mortality,respiration, feeding and swimming behavior in Calanus marshallae,Metridia pacifica and Euphausia pacifica

We report the laboratory survival, respiration, feeding and swimming behavior of zooplankton exposed to suspended tailing from a molybdenum mine that discharged into the Observatory Inlet fjord system in northern British Columbia. Test species were the copepods Calanus marshallae and Metridia pacifica and the euphausiid Euphausia pacifica. In the inlet, the discharge produced a turbid plume at intermediate depth and a near-bottom density flow down-slope into the deepest part of the fjord. The concentration of particles in the intermediate plume was always less than 15 mg liter⁻¹ at 0·5 km from the outfall and declined with increasing distance.In toxicity experiments the lowest whole tailing solids concentration that produced a clear decrease in median survival time was 560 mg liter⁻¹ for Euphausia pacifica at 112 h and Calanus marhallae at 464 h. All three test species ingested tailing particles. In several cases the presence of low tailing concentrations increased survival over that in filtered seawater. Oxygen consumption was affected at relatively low tailing concentration. The pattern of respiratory responses varied with species and nutritional condition. The swimming behavior of Calanus marshallae could be partitioned into five stereotypic patterns, of which one, “circles”, was associated with continuous feeding. ‘Circles’ was induced in Calanus when starved animals were fed a culture of the diatom Thalassiosira fluviatilis. ‘Circles’ was neither induced nor extinguished by the presence of tailing.