Abstract
The European eel (Anguilla anguilla) has attracted scientific inquiry for centuries due to its singular biological traits. Within the European Union, glass eel fisheries have declined sharply since 1980, from up to 2000 t (t) to 62.2 t in 2018, placing wild populations under higher risk of extinction. Among the major causes of glass eels collapse, climate change has become a growing worldwide issue, specifically ocean warming and acidification, but, to our knowledge, data on physiological and biochemical responses of glass eels to these stressors is limited. Within this context, we selected some representative biomarkers [e.g. glutathione peroxidase (GPx), catalase (CAT), total antioxidant capacity (TAC), heat shock proteins (HSP70), ubiquitin (Ub) and DNA damage] to study physiological responses of the European glass eel under distinct laboratory-climate change scenarios, such as increased water temperature (+ 4 °C) and pH reduction (− 0.4 units), for 12 weeks. Overall, the antioxidant enzymatic machinery was impaired, both in the muscle and viscera, manifested by significant changes in CAT, GPx and TAC. Heat shock response varied differently between tissues, increasing with temperature in the muscle, but not in the viscera, and decreasing in both tissues under acidification. The inability of HSP to maintain functional protein conformation was responsible for boosting the production of Ub, particularly under warming and acidification, as sole stressors. The overproduction of reactive oxygen species (ROS), either elicited by warming - due to increased metabolic demand - or acidification - through H+ interaction with O2−, generating H2O2 - overwhelmed defense mechanisms, causing oxidative stress and consequently leading to protein and DNA damage. Our results emphasize the vulnerability of eels' early life stages to climate change, with potential cascading consequences to adult stocks.
Highlights
Wild populations of the European eel (Anguilla anguilla) are facing a serious risk of extinction and have been classified as ‘critically endangered’ by the International Union for the Conservation of Nature (IUCN) for more than a decade
An increase of 4 °C in water temperature resulted in higher glass eel mortality, while ocean acidification (OA) played a minor role on eels survival
The bulk of knowledge gathered on fish physiology states highly variable results among fish species to OArelated conditions
Summary
Wild populations of the European eel (Anguilla anguilla) are facing a serious risk of extinction and have been classified as ‘critically endangered’ by the International Union for the Conservation of Nature (IUCN) for more than a decade. Recruitment of European glass eels (i.e. the postlarval phase corresponding to the freshwater colonizing stage arriving from the southwestern part of the Sargasso Sea, where reproduction takes place, to continental waters) collapsed dramatically from the early 1980's onwards, from up to 2000 t (t) to 62.2 t in 2018 (ICES, 2019). The declining trend in juvenile eel recruitment has sparked significant scientific inquiry and it is consensual that anthropogenic pressure is greatly contributing for this collapse. Drouineau et al (2018) summarized five main drivers for eels decline: i) overexploitation at all their stages; ii) fragmentation and habitat loss; iii) increased contamination load; iv) alien parasitoid species (e.g. Anguillicola crassus); and v) global warming and oceanic physical modifications. The spawning migration of silver eels showed to be affected by alterations in river discharges and precipitation regimes (Drouineau et al, 2017, 2018; Durif et al, 2003)
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