Effects of emamectin benzoate spiked sediment on adult, larval and post-larval stages of the American lobster (Homarus americanus)

Salmon farming represents a significant economic sector on both Canada's Atlantic and Pacific coasts. To manage sea lice outbreaks, medicated feeds containing emamectin benzoate (EMB) are commonly applied. Because EMB is poorly soluble and highly persistent, it can settle in marine sediments and remain available to non-target species for months to years. The American lobster ( Homarus americanus ), a commercially important species in the Northwest Atlantic, often inhabits areas near aquaculture sites. This spatial overlap raises concerns about possible exposure to aquaculture therapeutants, highlighting the need to better understand their effects through multiple exposure pathways. In a previous study, the exposure of gravid female American lobsters to EMB-spiked sediment was investigated with a 10-day laboratory exposure. Results showed that a single, 10-day exposure of ovigerous females to EMB concentrations higher than environmentally relevant values did not affect females or the first larval stages. Here, similar effects of sediment spiked with EMB were investigated with a longer exposure (≥27 days) of adult ovigerous female lobsters and an assessment of later offspring developmental stages. Adult female survival, hatching success, offspring abnormalities, size, and molting success to the first benthic stage (Stage IV) were monitored after an exposure to EMB in sediments at a concentration 5 to 21 times higher than the upper range of average EMB concentrations detected at sites. Results show no effects on adults and first larval stage, confirming the previous findings, but effects on Stage II and Stage IV, with a potential to affect the recruitment and size of juvenile lobsters. • Ovigerous lobsters were exposed to a high concentration of EMB in sediment. • After hatching, larvae were reared in natural seawater without EMB. • EMB did not affect ovigerous adult lobsters mortality and hatching ability. • Exposure to EMB did not affect larval Stage I size, weight, and abnormalities. • Significantly fewer larvae reached Stage IV, exhibiting reduced carapace length.