Aerobic performance of two tropical cephalopod species unaltered by prolonged exposure to projected future carbon dioxide levels

Abstract

Squid and many other cephalopods live continuously on the threshold of their environmental oxygen limitations. If the abilities of squid to effectively take up oxygen are negatively affected by projected future carbon dioxide (CO₂) levels in ways similar to those demonstrated in some fish and invertebrates, it could affect the success of squid in future oceans. While there is evidence that acute exposure to elevated CO₂ has adverse effects on cephalopod respiratory performance, no studies have investigated this in an adult cephalopod after relatively prolonged exposure to elevated CO₂ or determined any effects on aerobic scope. Here, we tested the effects of prolonged exposure (≥20% of lifespan) to elevated CO₂ levels (~1000 μatm) on the routine and maximal oxygen uptake rates, aerobic scope and recovery time of two tropical cephalopod species, the two-toned pygmy squid, Idiosepius pygmaeus and the bigfin reef squid, Sepioteuthis lessoniana. Neither species exhibited evidence of altered aerobic performance after exposure to elevated CO₂ when compared to individuals held at control conditions. The recovery time of I. pygmaeus under both control and elevated CO₂ conditions was less than 1 hour, whereas S. lessoniana required approximately 8 hours to recover fully following maximal aerobic performance. This difference in recovery time may be due to the more sedentary behaviours of I. pygmaeus. The ability of these two cephalopod species to cope with prolonged exposure to elevated CO₂ without detriment to their aerobic performance suggests some resilience to an increasingly high CO₂ world.

Keywords: Aerobic scope; CO2 respirometry; cephalopod; ocean acidification; oxygen uptake.

Figure 1

Routine (white boxes) and maximal oxygen uptake (grey boxes) of pygmy squid (A) and bigfin reef squid (B) from current day control and elevated CO₂ treatments; boxplots show the median and interquartile range and the minimum and maximum range of the data.

Figure 2

Absolute aerobic scope of pygmy squid (A) and bigfin reef squid (B) from current day control and elevated CO₂ treatments; boxplots show the median and interquartile range and the minimum and maximum range of the data.

Figure 3

Recovery time that pygmy squid (A) and bigfin reef squid (B) required to reach a stable routine oxygen uptake rate following exhaustive exercise at current-day control and elevated CO₂ treatment levels; boxplots show the median and interquartile range and the minimum and maximum range of the data (Note: the y-axis for pygmy squid ranges from 0–150 minutes while the y-axis for bigfin reef squid ranges from 0–800 minutes).