The impact of ocean acidification and warming on the skeletal mechanical properties of the sea urchin Paracentrotus lividus from laboratory and field observations

Abstract

Increased atmospheric CO2 concentration is leading to changes in the carbonate chemistry and the temperature of the ocean. The impact of these processes on marine organisms will depend on their ability to cope with those changes, particularly the maintenance of calcium carbonate structures. Both a laboratory experiment (long-term exposure to decreased pH and increased temperature) and collections of individuals from natural environments characterized by low pH levels (individuals from intertidal pools and around a CO2 seep) were here coupled to comprehensively study the impact of near-future conditions of pH and temperature on the mechanical properties of the skeleton of the euechinoid sea urchin Paracentrotus lividus. To assess skeletal mechanical properties, we characterized the fracture force, Young's modulus, second moment of area, material nanohardness, and specific Young's modulus of sea urchin test plates. None of these parameters were significantly affected by low pH and/or increased temperature in the laboratory experiment and by low pH only in the individuals chronically exposed to lowered pH from the CO2 seeps. In tidal pools, the fracture force was higher and the Young's modulus lower in ambital plates of individuals from the rock pool characterized by the largest pH variations but also a dominance of calcifying algae, which might explain some of the variation. Thus, decreases of pH to levels expected for 2100 did not directly alter the mechanical properties of the test of P. lividus. Since the maintenance of test integrity is a question of survival for sea urchins and since weakened tests would increase the sea urchins' risk of predation, our findings indicate that the decreasing seawater pH and increasing seawater temperature expected for the end of the century should not represent an immediate threat to sea urchins vulnerability.

Effects of ocean acidification on the shells of four Mediterranean gastropod species near a CO2 seep

“…Much of this decline in biodiversity is due to reductions in the presence of calcifying marine organisms including scleractinian corals, mollusks and echinoderms (Inoue et al, 2013;Fabricius et al, 2014;Garilli et al, 2015). Species that do survive under acidified conditions may become more vulnerable to predation due to weakened shells/skeletons and are often smaller due to dissolution or physiological stress (Rodolfo-Metalpa et al, 2015;Langer et al, 2014;Collard et al, 2016;Newcomb et al, 2015;Harvey et al, 2016).…”

Ocean acidification reduces mechanical properties of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis

“…However, the effects of increased pCO2 on shell mechanical properties are species-specific. Near-future decreased pH 7.8 did not affect shell hardness in the sea urchin Paracentrotus lividus (Collard et al, 2016) or in the barnacle Amphibalanus amphitrite (McDonald et al, 2009). Indeed, juvenile oysters of C. gigas significantly increased their shell strength and size as a compensatory adaptive response to the 310 high pCO2 condition (i.e., pCO2 1000 µatm) (Wright et al, 2014), and the blue mussel, Mytilus edulis, produced a stiffer and harder calcite layer under in increased pCO2 condition (i.e., pCO2 1000 µatm) (Fitzer et al, 2015).…”

“…The decreased pH depletes carbonate ions necessary for CaCO3 mineralization chemically, as well as weakens marine organisms physiologically by causing acidosis and impairing internal pH homeostasis needed for 55 optimal calcification (Dupont and Portner, 2013) . Recently, an increasing number of studies capture the importance of the mechanical properties of calcareous shell, the end-products of calcification, under OA scenario (Dickinson et al, 2012;Ivanina et al, 2013;Li et al, 2014;Fitzer et al, 2015;Collard et al, 2016;Teniswood et al, 2016;Milano et al, 2016).…”

Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change

“…That said, species living in naturally acidified habitats (e.g. intertidal, CO 2 seeps) are a portent of the potential for acclimatization and/or adaptation to acidification (Collard et al, 2015; Migliaccio et al, 2019).…”