Effects of environmental hypercapnia and metal (Cd and Cu) exposure on acid-base and metal homeostasis of marine bivalves

Abstract

Elevated CO2 levels reduce seawater pH and may affect bioavailability of trace metals in estuaries. We studied the interactive effects of common metal pollutants (50 μg l(-1) Cd or Cu) and PCO2 (~395, 800 and 2000 μatm) on metal levels, intracellular pH, expression of metal binding proteins and stress biomarkers in estuarine bivalves Crassostrea virginica (oysters) and Mercenaria mercenaria (hard clams). Cd (but not Cu or hypercapnia) exposure affected the acid-base balance of hemocytes resulting in elevated intracellular pH. Cd and Cu exposure led to the increase in the tissue metal burdens, and metal accumulation was reduced by elevated PCO2 in the mantle but not hemocytes. No change was found in the intracellular free Cd(2+), Cu(2+) or Fe(2+) during Cu or Cd exposure indicating that these metals are bound to intracellular ligands. Free Zn(2+) content in oyster hemocytes was suppressed by Cd and Cu exposure and below the detection limits in clam hemocytes, which went hand-in-hand with the elevated mRNA expression of metallothioneins and ferritin in Cd- and Cu-exposed bivalves, enhanced by hypercapnia. The metal-binding and antioxidant mechanisms of oysters and clams were sufficient to effectively maintain intracellular redox status, even though metal exposure combined with moderate hypercapnia (~800 μatm PCO2) led to the elevated production of reactive oxygen species in hemocytes. Overall, while hypercapnia modulates metal accumulation, binding capacity and oxidative stress in estuarine bivalves, the physiological effects of elevated CO2 are mild compared to the effects of other common stressors.

Indirect effects of climate changes on cadmium bioavailability and biological effects in the Mediterranean mussel Mytilus galloprovincialis

“…especially cadmium and pH/pCO 2 . A similar interaction was observed in haemocytes of oysters exposed to cadmium and low pH (Ivanina et al, 2015), and further corroborated by the prooxidant effect of hypercapnia occurring in oysters, clams and polychaetes (Tomanek et al, 2011;Freitas et al, 2016a,b;Velez et al, 2016). A different modulatory effect of temperature and/or pH/pCO 2 was observed on metallothioneins levels in gills, where these factors appeared to lower the inductive capacity of cadmium.…”

Investigations of temperature and pH variations on metal trophic transfer in turbot (Scophthalmus maximus)

“…In contrast to temperature, fewer studies investigated the influence of pH on the assimilation of metals by marine biota (Lacoue-Labarthe et al 2011;Götze et al 2014;Ivanina et al 2015), and to the best of our knowledge, even none has investigating the influence of pH on metal trophic transfer in fish. However, in the context of the current ocean acidification, some authors have recently highlighted the effects of the partial pressure of CO2 (pCO2) on the digestion of fish (Pimentel et al 2015;Rosa et al 2016).…”

Changes in the biochemical and nutrient composition of seafood due to ocean acidification and warming

“…Since bivalves are filter feeders, they readily accumulate metals present in the surrounding waters into their edible tissue (Lu et al, 2017;Raposo et al, 2009). This process can be modulated by ocean acidification, for instance enhancing the bioaccumulation of Cu in oysters (Belivermiş et al, 2015;Götze et al, 2014;Hawkins & Sokolova, 2017;Ivanina et al, 2015;Ivanina et al, 2016). While Cu accumulation under ocean acidification and warming can come at metabolic costs to organisms (Hawkins & Sokolova, 2017) emissions.…”