Habitat selection disruption and lateralization impairment of cryptic flatfish in a warm, acid, and contaminated ocean

Abstract

Anthropogenic release of greenhouse gases is leading to significant changes in ocean physicochemical properties. Although marine organisms will have to deal with combined effects of ocean warming and acidification, little is known about the impact of interactions between these climate change variables and contaminants. Nowadays, mercury emissions are mostly of anthropogenic origin, and part of these emissions is deposited in the ocean sediment. Within this context, our goal was to determine the acclimation potential of a benthic flatfish, Solea senegalensis, to future climate change scenarios and methylmercury (MeHg) neurotoxicity. After 28 days of exposure under three-factor crossed treatments of MeHg contamination (non-contaminated and contaminated feed, 0.08 ± 0.02 and 8.51 ± 0.15 mg kg−1 dry weight, respectively), high CO2 (ΔCO2 ≈ 500 ppm), and temperature (ΔT = 4 °C), we investigated brain mercury accumulation, habitat preference, and relative/absolute lateralization, as well as acetylcholinesterase (AChE) activity in five brain regions. Our results indicate a differential effect of hypercapnia (decrease) on brain mercury accumulation. MeHg-contaminated flatfish displayed decreased AChE activity, impaired lateralization, and bottom choosing judgment. Contaminated fish spent significantly higher amounts of time in the complex habitat, where they could neither bury nor match the background. While warming led to higher enzymatic activity, acidification decreased Hg accumulation, but also affected AChE activity and disrupted habitat selection. Present-day MeHg environmental concentrations may lead to severe disruption of behavioral and neurological functions, which, combined with ocean warming and acidification, might further jeopardize the ecological fitness of flatfish.