Living in a high CO₂ world: a global meta‐analysis shows multiple trait‐mediated fish responses to ocean acidification

Abstract

Understanding how marine organisms will be affected by global change is of primary importance to ensure ecosystem functioning and nature contributions to people. This study meets the call for addressing how life‐history traits mediate effects of ocean acidification on fish. We built a database of overall and trait‐mediated responses of teleost fish to future CO2 levels by searching the scientific literature. Using a meta‐analytical approach, we investigated the effects of projected CO2 levels by IPCC for 2050–2070 and 2100 on fish eco‐physiology and behavior from 320 contrasts on 42 species, stemming from polar to tropical regions. Moreover, since organisms may experience a mosaic of carbonate chemistry in coastal environments (e.g., in estuaries, upwelling zones and intertidal habitats), which may have higher pCO2 values than open ocean waters, we assessed responses from additional 103 contrasts on 21 fish species using pCO2 levels well above IPCC projections. Under mid‐century and end‐of‐century CO2 emission scenarios, we found multiple CO2‐dose‐dependent effects on calcification, resting metabolic rate, yolk, and behavioral performances, along with increased predation risk and decreased foraging, particularly for larvae. Importantly, many of the traits considered will not confer fish tolerance to elevated CO2 and far‐reaching ecological consequences on fish population replenishment and community structure will likely occur. Extreme CO2 levels well above IPCC projections showed effects on fish mortality and calcification, while growth, metabolism, and yolk were unaffected. CO2 exposures in short‐term experiments increased fish mortality, which in turn decreased in longer‐term exposures. Whatever the elevated CO2 levels considered, some key biological processes (e.g., reproduction, development, habitat choice) were critically understudied. Fish are an important resource for livelihoods in coastal communities and a key component for stability of marine ecosystems. Given the multiple trait‐mediated effects evidenced here, we stress the need to fill the knowledge gap on important eco‐physiological processes and to expand the number and duration of ocean acidification studies to multi‐generational, multiple stressor (e.g., warming, hypoxia, fishing), and species interactions experiments to better elucidate complex ecosystem‐level changes and how these changes might alter provisioning of ecosystem services.

Divergent responses of Atlantic cod to ocean acidification and food limitation

“…A recent meta‐analyses revealed that the data basis is still too limited to allow for generalizations with regard to ocean acidification effects on growth among fish species (Cattano, Claudet, Domenici, & Milazzo, ). The strong interaction between food supply and CO 2 treatment on growth and development observed in this study highlights that food regime is important in assessing the impacts of ocean acidification on marine fishes.…”

You Better Repeat It: Complex CO2 × Temperature Effects in Atlantic Silverside Offspring Revealed by Serial Experimentation

“…Whole lifecycle effects of elevated CO 2 exposure remain critically understudied in fish [25]. While acclimation to chronic hypercapnia likely has small metabolic costs [86], over longer timescales tradeoffs associated with increased acid/base regulation could compromise other physiological processes [43].…”

“…LnRRs evaluate the average proportional change in a trait relative to control treatments, with negative lnRRs indicating negative CO 2 effects. LnRRs have become a common metric for evaluating CO 2 effects in meta-analyses when comparing variable responses across studies [6,25,74]. LnRRs were calculated as: lnRR(T) = ln(T high or extreme CO2 ) − ln(T control CO2 ).…”

Proteomic responses to ocean acidification in the brain of juvenile coral reef fish

“…Rising CO2 levels in the ocean are anticipated to affect the physiology and behaviour of marine organisms, with possible impacts on the structure and function of marine ecosystems (Wittmann and Pörtner, 2013;Cattano et al, 2018;Pörtner et al, 2019).…”