Impaired riverward migration behaviour of glass eels under climate change

Chair: Martin Grosell

Tiago F. Grilo1, José R. Paula1, Marta S. Pimentel1, Catarina Santos1, Rui Rosa1


1 MARE – Marine and Environmental Sciences Centre, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Av. Nossa Senhora do Cabo

939, 2750-374, Cascais, Portugal


Background: Eels are catadromous species of unquestionable ecological and economical relevance, reflecting quite well the environmental health and integrity of aquatic systems, from freshwater to the open sea. Upon arrival to the continental shelf the leptocephalus larva of the European eel (Anguilla anguilla) metamorphoses into juvenile glass eels. They orientate towards freshwater habitats using inland water odors (e.g. geosmin), temperature and salinity gradients. Odors are among the most important cues in glass eels migration, however their role in freshwater attractiveness  remains  poorly  understood.  Predicted  changes  in  Earth’s  climate might influence glass eels migration and olfactory sensitivity. Thus, the main goal was to evaluate the effects of ocean warming (∆ +3ºC) and high pCO2, with concomitant acidification (ΔpH −0.5 units) on glass eels behavior, specifically on their ability to detect olfactory cues.

Methods: The cues tested were geosmin, salinity and water flow. Animals were collected in three areas of the Minho estuary (mouth, intermediate and upstream), in Portugal, trying to reflect a salinity gradient. Responsiveness was measured according to the percentage of time that glass eels stayed on the cue.

Findings: Time spent by control organisms in all the cues tested was always higher than 65%. Under a warming scenario, glass eels responded in a similar way to the different cues as the control animals, suggesting that warming individually might not interfere with their sensory ability. Nevertheless, acidification by itself and the combined scenario of warming and acidification seem to have a disruptive effect in olfactory capacity, most evident for the glass eels under at higher salinities and tested for geosmin. Responsiveness in these cases declined significantly in relation to the controls, varying around 35%.

Conclusions:   Facing   these   results   if   acidification   continues   unabated,   the impairment of sensory ability will likely reduce eels population sustainability, with potentially profound consequences for marine diversity.