Ocean acidification as a multiple driver: how interactions between changing seawater carbonate parameters affect marine life

Abstract

‘Multiple drivers’ (also termed ‘multiple stressors’) is the term used to describe the cumulative effects of multiple environmental factors on organisms or ecosystems. Here, we consider ocean acidification as a multiple driver because many inorganic carbon parameters are changing simultaneously, including total dissolved inorganic carbon, CO2, HCO3–, CO32–, H+ and CaCO3 saturation state. With the rapid expansion of ocean acidification research has come a greater understanding of the complexity and intricacies of how these simultaneous changes to the seawater carbonate system are affecting marine life. We start by clarifying key terms used by chemists and biologists to describe the changing seawater inorganic carbon system. Then, using key groups of non-calcifying (fish, seaweeds, diatoms) and calcifying (coralline algae, coccolithophores, corals, molluscs) organisms, we consider how various physiological processes are affected by different components of the carbonate system.

Lower Salinity Leads to Improved Physiological Performance in the Coccolithophorid Emiliania huxleyi, Which Partly Ameliorates the Effects of Ocean Acidification

“…Seawater acidification has also been shown to inhibit growth rate of E. huxleyi in other studies (Nimer et al, 1994;Hoppe et al, 2011). Ocean acidification has the dual effect of increasing pCO 2 but also increasing H + concentration, parameters that can have different effects on cellular performance (Hurd et al, 2020). Utilization of HCO 3 − to provide CO 2 in photosynthesis generates OH − , driving the pH up, while calcification consumes OH − , driving the pH down.…”

Effects of multiple drivers of ocean global change on the physiology and functional gene expression of the coccolithophore Emiliania huxleyi

“…In addition, nitrogen is an important component of the enzyme RubisCO, the activity of which controls cellular organic carbon fixation (Sciandra et al., 2003). The decreased pH (i.e., increased H + concentration as a consequence of CO 2 enrichment; Hurd et al, 2020) in the CO 2 ‐ N treatment may lead to an instantaneous change in the internal pH in E. huxleyi cells, and nitrogen deficiency can further impair the cellular pH regulatory capacity (Suffrain, Schulz, Gutowska, Riebesell, & Bleich, 2011). Therefore, we suggest that the lower internal pH in the CO 2 ‐N treatment, compared to either the rising p CO 2 or decreasing nitrate concentration alone, may further depress the growth and photosynthesis of E. huxleyi (Nimer, Brownlee, & Merrett, 1994; Nimer & Merrett, 1993), causing synergistic negative effects on both growth and photosynthetic rates.…”

Acidification in the U.S. Southeast: Causes, Potential Consequences and the Role of the Southeast Ocean and Coastal Acidification Network

“…The form of calcium carbonate mineral most commonly used by organisms is aragonite or calcite; the decrease in carbonate results in a lower aragonite saturation state ( arag ) or calcite saturation state ( cal ) meaning that skeletons made of aragonite or calcite will be energetically more difficult to form (Kleypas et al, 2006;Fabry et al, 2008). Other studies suggest that some calcifying organisms such as mollusks and corals use other forms of DIC (e.g., bicarbonate) moreso than carbonate for calcification (Hurd et al, 2019) and that increasing proton concentrations [H + ] (reduced pH) are more influential on calcification (Cyronak et al, 2015;Comeau et al, 2018;Hurd et al, 2019). Nonetheless, the U.S. Southeast is rich in economically important calcifying organisms that use calcium carbonate to build their shells and skeletons.…”