Physiological advantages of dwarfing in surviving extinctions in high-CO2 oceans

Abstract

Excessive CO 2 in the present-day ocean-atmosphere system is causing ocean acidification, and is likely to cause a severe biodiversity decline in the future, mirroring effects in many past mass extinctions. Fossil records demonstrate that organisms surviving such events were often smaller than those before, a phenomenon called the Lilliput effect. Here, we show that two gastropod species adapted to acidified seawater at shallow-water CO 2 seeps were smaller than those found in normal pH conditions and had higher mass-specific energy consumption but significantly lower whole-animal metabolic energy demand. These physiological changes allowed the animals to maintain calcification and to partially repair shell dissolution. These observations of the long-term chronic effects of increased CO 2 levels forewarn of changes we can expect in marine ecosystems as CO 2 emissions continue to rise unchecked, and support the hypothesis that ocean acidification contributed to past extinction events. The ability to adapt through dwarfing can confer physiological advantages as the rate of CO 2 emissions continues to increase

Effects of low-pH stress on shell traits of the dove snail, <i>Anachis misera</i>, inhabiting shallow-vent environments off Kueishan Islet, Taiwan

“…In contrast, shell dissolution is absent at normalpH sites. The nassariid gastropods Nassarius corniculus and Cyclope neritea adapted to the Ischia vent were smaller than those found in normal-pH conditions and had a higher massspecific energy consumption but a significantly lower wholeanimal metabolic energy demand (Garilli et al, 2015). Compared with deep-sea vent studies, on the northwest of Eifuku Volcano, Mariana Arc, the vent mussel Bathymodiolus brevior, inhabiting low-pH environments (pH 5.36-7.29), exhibited a shell thickness and daily growth increments in shells of only about half of that of mussels living in environments with pH > 7.8 (Tunnicliffe et al, 2009).…”

Calcification and inducible defence response of a calcifying organism could be maintained under hypoxia through phenotypic plasticity

“…While ocean acidification was expected to retard calcification (Orr et al, 2005), it is now realized that calcification is not primarily driven by the pH and carbonate saturation state of seawater (Roleda et 35 al., 2012), meaning that the impact of ocean acidification on calcifying organisms through the changes in seawater carbonate chemistry is less deleterious than previously thought (e.g. Garilli et al, 2015;Ramajo et al, 2016;Leung et al, 2017). Indeed, calcification is an energy-dependent physiological process actively regulated by calcifying organisms (Roleda et al, 2012).…”

Species interactions can shift the response of a maerl bed community to ocean acidification and warming

“…The response of G l to temperature and pCO 2 changes was complex. The interaction between temperature and pCO 2 observed in the summer may cause changes in energy partitioning, thereby inducing a trade-off between metabolic processes at the expense of respiration and excretion (Garilli et al, 2015). However, the effect of temperature and pCO 2 on the calcification of P. miliaris must be considered carefully.…”