Abstract

Rising atmospheric carbon dioxide levels are driving decreases in aquatic pH. As a result, there has been a surge in the number of studies examining the impact of acidification on aquatic fauna over the past decade. Thus far, both positive and negative impacts on the growth of fish have been reported, creating a disparity in results. Food availability and single‐generation exposure have been proposed as some of the reasons for these variable results, where unrealistically high food treatments lead to fish overcoming the energetic costs associated with acclimating to decreased pH. Likewise, exposure of fish to lower pH for only one generation may not capture the likely ecological response to acidification that wild populations might experience over two or more generations. Here we compare somatic growth rates of laboratory populations of the Trinidadian guppy (Poecilia reticulata) exposed to pH levels that represent the average and lowest levels observed in streams in its native range. Specifically, we test the role of maternal acclimation and resource availability on the response of freshwater fishes to acidification. Acidification had a negative impact on growth at more natural, low food treatments. With high food availability, fish whose mothers were acclimated to the acidified treatment showed no reduction in growth, compared to controls. Compensatory growth was observed in both control–acidified (maternal–natal environment) and acidified–control groups, where fish that did not experience intergenerational effects achieved the same size in response to acidification as those that did, after an initial period of stunted growth. These results suggest that future studies on the effects of shifting mean of aquatic pH on fishes should take account of intergenerational effects and compensatory growth, as otherwise effects of acidification may be overestimated.

Highlights

  • Anthropogenic carbon dioxide (CO2) emissions, including the burning of fossil fuels and deforestation, are a key driver in both freshwater and ocean acidifications (Quay, Tilbrook, & Wong, 1992)

  • It was proposed that the reason for reports of acidification having no effect on, or increasing, growth rate of juvenile fishes was due to the ad libitum food levels provided in a majority of studies masking the increased energetic cost associated with acclimating to an acidified environment, such as in several studies on juvenile marine fishes (Munday et al, 2009; Rossi et al, 2015)

  • This study was designed to assess the impact of CO2‐induced aquatic acidification on the growth of a freshwater fish

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Summary

| INTRODUCTION

Anthropogenic carbon dioxide (CO2) emissions, including the burning of fossil fuels and deforestation, are a key driver in both freshwater and ocean acidifications (Quay, Tilbrook, & Wong, 1992). A meta‐analysis concluded that ocean acidification has an overall positive effect on fish growth (Kroeker, Kordas, Crim, & Singh, 2010), with more recent studies continuing to find similar results (Rossi et al, 2015) Both enhanced aerobic scope and increased routine metabolic rate have been reported in fish exposed to near‐future CO2 levels (Miller, Watson, Donelson, McCormick, & Munday, 2012; Rummer et al, 2013). When under high metabolic demand, for example during the larval life stage, the increased energetic cost associated with compensatory mechanisms may lead to energetic deficit in acidified fish (Stiasny et al, 2018) This effect may be exacerbated when feeding is limited, as is often the case for wild fish larvae (MacKenzie, Leggett, & Peters, 1990). We expect fish in more acidified treatments to grow more slowly under lower food treatments, but not in higher ad libitum food treatments and fish born into novel environments to grow more slowly than those born into environments that their mothers were acclimated to at preparturition

| MATERIALS AND METHODS
| Experimental setup
| DISCUSSION
Findings
| CONCLUSION
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