Abstract
ABSTRACTCarbon dioxide (CO2) levels projected to occur in the oceans by the end of this century cause a range of behavioural effects in fish, but whether other highly active marine organisms, such as cephalopods, are similarly affected is unknown. We tested the effects of projected future CO2 levels (626 and 956 µatm) on the behaviour of male two-toned pygmy squid, Idiosepius pygmaeus. Exposure to elevated CO2 increased the number of active individuals by 19–25% and increased movement (number of line-crosses) by nearly 3 times compared to squid at present-day CO2. Squid vigilance and defensive behaviours were also altered by elevated CO2 with >80% of individuals choosing jet escape responses over defensive arm postures in response to a visual startle stimulus, compared with 50% choosing jet escape responses at control CO2. In addition, more escape responses were chosen over threat behaviours in body pattern displays at elevated CO2 and individuals were more than twice as likely to use ink as a defence strategy at 956 µatm CO2, compared with controls. Increased activity could lead to adverse effects on energy budgets as well as increasing visibility to predators. A tendency to respond to a stimulus with escape behaviours could increase survival, but may also be energetically costly and could potentially lead to more chases by predators compared with individuals that use defensive postures. These results demonstrate that projected future ocean acidification affects the behaviours of a tropical squid species.
Highlights
Over the last 250 years, anthropogenic fossil fuel combustion and deforestation have increased atmospheric carbon dioxide (CO2) concentrations by almost 40% from 280 ppm to over 395 ppm (Collins et al, 2013)
The partial pressure of CO2 in the ocean increases as atmospheric CO2 levels rise, because the atmosphere and surface ocean are in approximate gas equilibrium (Doney, 2010)
Among active individuals only (n56–12), there was a significant difference in the mean number of line crosses among the control and elevated CO2 treatments (ANOVA: F2,2653.474, p50.046)
Summary
Over the last 250 years, anthropogenic fossil fuel combustion and deforestation have increased atmospheric carbon dioxide (CO2) concentrations by almost 40% from 280 ppm to over 395 ppm (Collins et al, 2013). On the current emissions trajectory, atmospheric CO2 is projected to exceed 900 ppm by 2100 and ocean pH will drop by a further 0.3–0.4 units compared with current-day values (Collins et al, 2013). Such dramatic changes to ocean chemistry could affect many marine organisms with potentially far-reaching impacts on marine ecosystems (Hoegh-Guldberg et al, 2007; Fabry et al, 2008; Doney et al, 2009)
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