Abstract
ABSTRACTPolar cod (Boreogadus saida) is an important prey species in the Arctic ecosystem, yet its habitat is changing rapidly: climate change, through rising seawater temperatures and CO2 concentrations, is projected to be most pronounced in Arctic waters. This study aimed to investigate the influence of ocean acidification and warming on maximum performance parameters of B. saida as indicators for the species' acclimation capacities under environmental conditions projected for the end of this century. After 4 months at four acclimation temperatures (0, 3, 6, 8°C) each combined with two PCO2 levels (390 and 1170 µatm), aerobic capacities and swimming performance of B. saida were recorded following a Ucrit protocol. At both CO2 levels, standard metabolic rate (SMR) was elevated at the highest acclimation temperature indicating thermal limitations. Maximum metabolic rate (MMR) increased continuously with temperature, suggesting an optimum temperature for aerobic scope for exercise (ASex) at 6°C. Aerobic swimming performance (Ugait) increased with acclimation temperature irrespective of CO2 levels, while critical swimming speed (Ucrit) did not reveal any clear trend with temperature. Hypercapnia evoked an increase in MMR (and thereby ASex). However, swimming performance (both Ugait and Ucrit) was impaired under elevated near-future PCO2 conditions, indicating reduced efficiencies of oxygen turnover. The contribution of anaerobic metabolism to swimming performance was very low overall, and further reduced under hypercapnia. Our results revealed high sensitivities of maximum performance parameters (MMR, Ugait, Ucrit) of B. saida to ocean acidification. Impaired swimming capacity under ocean acidification may reflect reduced future competitive strength of B. saida.
Highlights
The animals were kept in the aquaria of Havbruksstasjonen i Tromsø aerobic scope (AS) (HiT) until April 2013, when they were transported to the laboratories of the Alfred Wegener Institute (AWI) in Bremerhaven
The present study aimed to investigate oxygen consumption and exercise capacities of B. saida after long-term acclimation to future ocean acidification and warming (OAW) conditions in order to estimate the competitive strength of this species under future environmental conditions at PCO2 levels following the RCP8.5 scenario (IPCC, 2014)
Our results suggest that enhanced costs visible in elevated Maximum metabolic rate (MMR) under hypercapnic water conditions cause a reduction in maximum swimming capacity
Summary
These changes are expected to be fastest in Arctic waters due to the high solubility of CO2 in cold waters (Fransson et al, 2009), and an increase in the temperature of Atlantic water masses flowing into the Arctic ocean (Polyakov et al, 2010). This accelerates the decline in sea-ice cover and the freshening of surface waters (McPhee et al, 1998), which, in turn, exacerbates ocean acidification due to decreasing buffer capacities (Steinacher et al, 2009). Warming and potentially other climate change stressors such as ocean acidification appear to be already causing large-scale geographic shifts of marine species (Poloczanska et al, 2014) such as the ongoing borealization of the Arctic (Fossheim et al, 2015), entailing significant effects on the Arctic food chain
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