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 EC 50 values ranging from 0.14 to 0.24 μg 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 EC 50 values ranged from 0.12 μg L −1 ( T. longicornis nauplii) to >5 μg L −1 ( P. elongatus adults). For all species, nauplii and copepodite EC 50 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 μg L −1 ). Concentrations causing acute toxicity to planktonic copepods were lower than the recommended sea lice treatment concentration of 5 μg 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 μg 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.