Rising pCO2 in Freshwater Ecosystems Has the Potential to Negatively Affect Predator-Induced Defenses in Daphnia

Abstract

Anthropogenically released CO accumulates in the global carbon cycle and is anticipated to imbalance global carbon fluxes [1]. For example, increased atmospheric CO induces a net air-to-sea flux where the oceans take up large amounts of atmospheric CO (i.e., ocean acidification [2-5]). Research on ocean acidification is ongoing, and studies have demonstrated the consequences for ecosystems and organismal biology with major impacts on marine food webs, nutrient cycles, overall productivity, and biodiversity [6-9]. Yet, surprisingly little is known about the impact of anthropogenically caused CO on freshwater systems due to their more complex biogeochemistry. The current consensus, yet lacking data evidence, is that anthropogenic CO does indeed affect freshwater carbon hydrogeochemistry, causing increased pCO in freshwater bodies [10-13]. We analyzed long-term data from four freshwater reservoirs and observed a continuous pCO increase associated with a decrease in pH, indicating that not only the oceans but also inland waters are accumulating CO. We tested the effect of pCO-dependent freshwater acidification using the cosmopolite crustacean Daphnia. For general validity, control pCO-levels were based on the present global pCO average. Treatments were selected with very high pCO levels, assuming a continuous non-linear increase of pCO, reflecting worst-case-scenario future pCO levels. Such levels of elevated pCO reduced the ability of Daphnia to sense its predators and form adequate inducible defenses. We furthermore determined that pCO and not the resulting reduction in pH impairs predator perception. If pCO alters chemical communication between freshwater species, this perturbs intra- and interspecific information transfer, which may affect all trophic levels.

Influence of Nutritional Status on Carbon Dioxide Tolerance and Avoidance Behavior in a Freshwater Teleost

“…; Weiss et al. ). Although the mechanism responsible for this increase has not been identified and the consequences for aquatic ecosystems have not been well defined, results from the current study suggest that the sensitivity of freshwater fish to future increases in aquatic CO 2 may be influenced by individual nutritional status, making this an important area for future research.…”

Critically examining the knowledge base required to mechanistically project climate impacts: A case study of Europe's fish and shellfish

“…Fish and shellfish are potentially impacted by climate‐driven changes in a suite of abiotic factors beyond warming including the acidification of marine and freshwaters (Caldeira & Wickett, ; Weiss et al., ), deoxygenation (Altieri & Gedan, ) and altered precipitation and river flow rates in freshwater habitats (Ficke, Myrick, & Hansen, ; Markovic et al., ; Pletterbauer, Melcher, & Graf, ; Poff, Brinson, & Day, ; Ward, Anderson, Beechie, Pess, & Ford, ). Several studies have reviewed the effects of these physical changes on fish and shellfish in these habitats (e.g., Callaway et al., ; Petitgas et al., ; Robins et al., ).…”

The impact of water pH on association preferences in fish

“…Acidification occurs primarily as a result of acidified rain or snow depositions, whereby the emissions of sulphur dioxides and nitrogen oxides into the atmosphere form highly acidic precipitations that can have long‐lasting effects on freshwater pH (Galloway, Norton, & Church, ; Muniz, ). Aquatic ecosystems can also be affected by climate change‐related acidification due to the increased uptake of CO 2 from the atmosphere (Caldeira & Wickett, ; Weiss et al, ). Humic acid, a result of degrading organic matter, can be another cause of freshwater acidification (Steinberg, ).…”

“…acidification due to the increased uptake of CO 2 from the atmosphere (Caldeira & Wickett, 2005;Weiss et al, 2018). Humic acid, a result of degrading organic matter, can be another cause of freshwater acidification (Steinberg, 2013).…”

“…Experimental studies have shown that a reduction in freshwater pH can indeed change an animal's behavioural response towards chemical stimuli. For instance, acute and chronic exposure to a lower than normal water pH can interfere with the detection of foraging cues (Lemly & Smith, 1985Royce-Malmgren & Watson, 1987) and weaken or prevent predator avoidance behaviour (Leduc, Kelly, & Brown, 2004;Leduc, Roh, & Brown, 2009;Ou et al, 2015;Weiss et al, 2018). Reduced pH conditions have also been demonstrated to change the reproductive behaviour of aquatic animals (Ikuta, Munakata, Aida, Amano, & Kitamura, 2001;Ikuta et al, 2003;Johnson & Webster, 1977).…”