Potential effect of pesticides currently used in salmon farming on photo and chemoautotrophic carbon uptake in central – southern Chile

Aquaculture has become an important component of Chilean economy, especially in the southern region, where salmon farming is an active industry. However, high density in salmon cages can increase stress and susceptibility to parasitic outbreaks of the copepod Caligus rogercresseyi. The pesticides used against sea lice can have potential effects on non-target microbiota and on the structure and functioning of aquatic ecosystems. The objective of this study was to investigate the response of natural microbial communities to the addition of the anti-lice pesticides azamethiphos, deltamethrin and emamectin benzoate and their potential impact on photoautotrophic and chemoautotrophic carbon fixation in central-southern Chile (37°S to 42°S). The addition of pesticides on primary production samples was related to changes in carbon uptake, which were significant if a single pesticide was applied, mainly emamectin benzoate and azametiphos. In surface waters of central Chile, emamectin benzoate produced a 60–90% decrease for both photo and chemoautotrophic carbon fixation. Enhanced rates were also observed for in situ primary production as a result of azamethiphos addition in northern Patagonia. Such stimulation, although limited, was possibly related to the supply of nitrogen and phosphate for phytoplankton requirements by this organophosphate compound. •Anti-lice pesticides currently used in salmon farming produce variable effects in microbial carbon fixation.•Chemo and phototrophic carbon uptake can be affected by pesticides but results with pesticide combinations are variable.•Possible nutrient addition by organic compounds used as anti-lice treatment can affect phytoplankton dynamics.