Toxicity of the aquaculture pesticide cypermethrin to planktonic marine copepods

The acute and sublethal toxicity of cypermethrin, the active ingredient in the sea lice treatment formulation Excis, to non-target planktonic marine copepods was determined. The comparative sensitivities of three life stages (nauplii, copepodites, adults) of four common marine copepods (Acartia clausi, Pseudocalanus elongatus, Temora longicornis and Oithona similis) were assessed in 48-h exposures, followed by a recovery period in toxicant-free sea water. The cyclopoid copepod, O. similis, was most affected by cypermethrin, with EC50 values ranging from 0.14 to 0.24 )mu)g L^-1 for nauplii and adults respectively. With the exception of T. longicornis nauplii, the calanoid copepods (A. clausi, P. elongatus and T. longicornis) responded similarly to cypermethrin. Overall, 48-h EC50 values ranged from 0.12 (mu)g L^-1 (T. longicornis nauplii) to >5 (mu)g L^-1 (P. elongatus adults). For all species, nauplii and copepodite EC50 values were lower than those of the adults. The primary toxic effect, immobilization, was generally irreversible. A sublethal test with adult A. clausi females, involving pulse exposures over 4 days measured a significant increase in egg production at the higher concentrations (1.58 and 5 (mu)g L^-1). Concentrations causing acute toxicity to planktonic copepods were lower than the recommended sea lice treatment concentration of 5 (mu)g L^-1 cypermethrin, indicating the potential for toxic effects in the field. However, acute toxicity values were higher than the Environmental Quality Standard of 0.016 (mu)g L^-1 for dispersing treatment plumes, suggesting that cypermethrin released to the marine environment following sea lice treatments is unlikely to affect adversely planktonic copepods.