The lethal and sublethal effects of anti-sea lice chemotherapeutants in marine benthic and pelagic invertebrates

The salmon aquaculture industry has become a major contributor to the Canadian economy, however, many practices including sea lice pest management strategies have resulted in the contamination of the environment near these operations. Compounds used in sea lice control include Salmosan® (active ingredient [AI] azamethiphos), Paramove®50 (AI hydrogen peroxide), ivermectin (IVM) and SLICE® (AI emamectin benzoate [EMB]). Salmosan® and Paramove®50 are water-soluble formulations applied as bath treatments, whereas IVM and SLICE® are in-feed additives that are hydrophobic and partition to sediment with persistent physicochemical properties. This research assessed both the lethal and sub-lethal effects of these compounds on non-target benthic and pelagic invertebrates at environmentally relevant concentrations. A short-term fertilization success bioassay using the sea urchin Strongylocentrotus purpuratus was performed using pest management application-level concentrations of Salmosan® and Paramove®50 in seawater. Paramove®50 significantly inhibited fertilization success with a calculated IC50 value of 7.27 mg/L; Salmosan® only marginally inhibited fertilization at the highest concentration (IC50 > 100 µg/L). Avoidance behaviour and oxygen consumption were assessed in the benthic amphipod, Eohaustorius estuarius, and the polychaete Nereis virens, following sub-chronic exposure to environmentally relevant sediment concentrations (< 5 µg/kg) of EMB, IVM and a combination of both (EMB/IVM). E. estuarius avoided sediment containing IVM and EMB/IVM ratio concentrations containing 25 and 50 µg/kg IVM, while N. virens avoided sediment with 50 and 200 µg/kg IVM and 0.5, 5, 50 and 200 µg/kg EMB/IVM ratio. Impaired burrowing and locomotory behaviour in N. virens was also observed with both treatments. Oxygen consumption was significantly decreased in E. estuarius and increased in N. virens when exposed to EMB, IVM and EMB/IVM at concentrations < 5 µg/kg over a 28-d exposure period. This research provides evidence of impacts to S. purpuratus, E. estuarius and N. virens from anti-sea lice chemotherapeutant exposure at environmentally relevant concentrations and will supplement regulatory decisions and management policies associated with chemicals used in aquaculture in Canada.