Abstract
Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry. The perception that copepods are insensitive to OA is largely based on experiments with adult females. Their apparent resilience to increased carbon dioxide (pCO2 ) concentrations has supported the view that copepods are 'winners' under OA. Here, we show that this conclusion is not robust, that sensitivity across different life stages is significantly misrepresented by studies solely using adult females. Stage-specific responses to pCO2 (385-6000μatm) were studied across different life stages of a calanoid copepod, monitoring for lethal and sublethal responses. Mortality rates varied significantly across the different life stages, with nauplii showing the highest lethal effects; nauplii mortality rates increased threefold when pCO2 concentrations reached 1000μatm (year 2100 scenario) with LC50 at 1084μatm pCO2 . In comparison, eggs, early copepodite stages, and adult males and females were not affected lethally until pCO2 concentrations ≥3000μatm. Adverse effects on reproduction were found, with >35% decline in nauplii recruitment at 1000μatm pCO2 . This suppression of reproductive scope, coupled with the decreased survival of early stage progeny at this pCO2 concentration, has clear potential to damage population growth dynamics in this species. The disparity in responses seen across the different developmental stages emphasizes the need for a holistic life-cycle approach to make species-level projections to climate change. Significant misrepresentation and error propagation can develop from studies which attempt to project outcomes to future OA conditions solely based on single life history stage exposures.
Highlights
Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry
Nauplii were the most vulnerable developmental stage to be directly affected by increased levels of pCO2 (Figs 1b, f and 2), with significantly higher mortality rates compared to all other developmental stages (ANOSIM pairwise comparison, all P < 0.001)
Upon exposure to the near-future pCO2 level (1000 latm), nauplii showed a threefold increase in mortality rates (Mann–Whitney U Test, P = 0.029), with 100% mortality found upon exposure to 2000 latm pCO2
Summary
Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry. Previous studies exposing calanoid copepod species have highlighted their apparent resilience to the projected 2100 pCO2 (Weydmann et al, 2012; McConville et al, 2013), with lethal and sublethal effects occurring at concentrations that far surpass any climate change scenario (Yamada & Ikeda, 1999; Watanabe et al, 2006; Pascal et al, 2010) These studies have focused largely on the lethal and sublethal effects of acute high pCO2 on adult females (Kurihara et al, 2004a,b; Mayor et al, 2007, 2012; Pascal et al, 2010; Zervoudaki et al, 2011; Zhang et al, 2011; Vehmaa et al, 2012; McConville et al, 2013). As the projected levels of pCO2 will be variable over different temporal and spatial scales (Flynn et al, 2012), we argue that exposure of individuals to a range of pCO2 levels over relatively short periods of time would be similar to gradients that A.tonsa may experience in the wild
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