Ocean acidification increases copper toxicity differentially in two key marine invertebrates with distinct acid-base responses

Abstract

Ocean acidification (OA) is expected to indirectly impact biota living in contaminated coastal environments by altering the bioavailability and potentially toxicity of many pH-sensitive metals. Here, we show that OA (pH 7.71; pCO2 1480 μatm) significantly increases the toxicity responses to a global coastal contaminant (copper ~0.1 μM) in two keystone benthic species; mussels (Mytilus edulis) and purple sea urchins (Paracentrotus lividus). Mussels showed an extracellular acidosis in response to OA and copper individually which was enhanced during combined exposure. In contrast, urchins maintained extracellular fluid pH under OA by accumulating bicarbonate but exhibited a slight alkalosis in response to copper either alone or with OA. Importantly, copper-induced damage to DNA and lipids was significantly greater under OA compared to control conditions (pH 8.14; pCO2 470 μatm) for both species. However, this increase in DNA-damage was four times lower in urchins than mussels, suggesting that internal acid-base regulation in urchins may substantially moderate the magnitude of this OA-induced copper toxicity effect. Thus, changes in metal toxicity under OA may not purely be driven by metal speciation in seawater and may be far more diverse than either single-stressor or single-species studies indicate. This has important implications for future environmental management strategies.

Impacts of ocean acidification on sea urchin growth across the juvenile to mature adult life-stage transition is mitigated by warming

“…At pH 7.6, regardless of temperature, gonad development was reduced and in some individuals inhibited. The T. gratilla were able to compensate their acid-base balance in moderate acidification but less so in the lowest pH treatment, as reported for other sea urchin species [22,25,27,49]. Increased temperature caused acidification of the coelomic fluid, probably due to increased respiratory acidosis of the coelom.…”

“…Maintenance of organism acid -base balance is crucial for physiological function and is a significant energetic cost that affects energy partitioning between fitness traits such as growth and reproduction [25]. Several studies have shown that sea urchins can maintain their acid-base balance at near-future levels of acidification, but this is likely to be energetically costly [26,27], especially in combination with warming [28].…”

Hemocyte responses of the thick shell mussel Mytilus coruscus exposed to nano-TiO 2 and seawater acidification

“…Experts have predicted a drop in seawater pH by 0.3 to 0.4 units by the end of the century and concluded that average oceanic pH will decrease altogether by 0.8 units by 2300 (Caldeira and Wickett, 2003;Feely et al, 2009;IPCC, 2013). If such acidification trend continues to intensify, a wide range of marine invertebrate species (Fabry et al, 2008;Kroeker et al, 2013;Orr et al, 2005), including 63% of echinoderms and 51.6% of mollusks, will have difficulty maintaining healthy and normal physiological activities (Lewis et al, 2016). For example, the exposure to acidified seawater strongly affects immune parameters in Chamelea gallina and Mytilus galloprovincialis (Matozzo et al, 2013).…”

CO2-induced pH reduction increases physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus

“…Some studies show that CO 2 -induced pH reduction impacts bivalve physiology by changing extracellular acid–base balance2627, metabolic activities28 and feeding2930. A rise in pCO 2 levels can induce changes in the extracellular acid–base balance that can produce metabolic disturbances, adversely affecting relevant biological processes, such as calcification, metabolism, growth and fitness3132.…”