| Summary: | The oceans’ uptake of carbon dioxide from anthropogenic emissions will challenge marine organisms, as they will need to modulate their extracellular environment to cope with the surrounding hypercapnia. The gills represent the interface between the external and internal media and are the organ mostly involved in the compensatory regulation. Although crustaceans are thought to be relatively tolerant to higher levels of environmental CO2, comparatively little attention has been given to non-decapod species. In this study I investigated the effect of prolonged (65 days) exposure to elevated pCO2 on the gills of juvenile amphipods Echinogammarus marinus. Newly hatched juveniles were reared at pCO2 seawater concentrations predicted to occur over the next 100 yr (750 ppm) by the IPCC WRE750 stabilization scenario. Metabolic rates, Na+/K+-ATPase activity, pleopod beats as well as morphometric gills dimensions were measured. Overall, acclimation to elevated pCO2 did not lead to changes in the capacity for respiration and osmo-ionic regulation in the gills of juvenile amphipods. Similarly, no consistent variation in the gills ventilation through pleopod beats was found. Finally, gills morphometric dimensions were not affected by elevated pCO2. However it appears that CO2 had a significant effect on the gills allometric growth, interacting differently among gills. It is concluded that the functional and morphological traits in the gills of juveniles E. marinus will enable them to be resilient to higher pCO2 levels.
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