Abstract
Behavioural impairment following exposure to ocean acidification-relevant CO2 levels has been noted in a broad array of taxa. The underlying cause of these disruptions is thought to stem from alterations of ion gradients across neuronal cell membranes that occur as a consequence of maintaining pH homeostasis via the accumulation of . While behavioural impacts are widely documented, few studies have measured acid–base parameters in species showing behavioural disruptions. In addition, current studies examining mechanisms lack resolution in targeting specific neural pathways corresponding to a given behaviour. With these considerations in mind, acid–base parameters and behaviour were measured in a model organism used for decades as a research model to study learning, the California sea hare (Aplysia californica). Aplysia exposed to elevated CO2 increased haemolymph , achieving full and partial pH compensation at 1200 and 3000 µatm CO2, respectively. Increased CO2 did not affect self-righting behaviour. In contrast, both levels of elevated CO2 reduced the time of the tail-withdrawal reflex, suggesting a reduction in antipredator response. Overall, these results confirm that Aplysia are promising models to examine mechanisms underlying CO2-induced behavioural disruptions since they regulate and have behaviours linked to neural networks amenable to electrophysiological testing.
Highlights
Ocean acidification is occurring at rates not observed in the last 300 million years
Aplysia exposed to CO2 for 4–11 days showed a significant reduction in haemolymph pHe at 3000 (t = −2.736, p = 0.021), but not at 1200 μatm CO2 when compared with controls
Aplysia exposed to elevated CO2 (1200 and 3000 μatm CO2) were able to accumulate significantly higher levels of HCOÀ3 in haemolymph following a 4–11 day exposure period
Summary
Ocean acidification is occurring at rates not observed in the last 300 million years. Increase from current levels of approximately 400 to approximately 940 μatm CO2 by the end of the century 2 and approximately 1900 μatm CO2 by the year 2300 unless the rate of CO2 emissions is substantially curtailed [1,2,3]. This rapid rate of change has made predicting the sensitivity of organisms to future predicted CO2 levels a major focus of climate change research. Studies focused heavily on calcifying invertebrates, reporting widespread impacts to calcification and growth [4]. Fish exposed to CO2 have exhibited alterations to mitochondrial pathways, intestinal base secretion and otolith growth [5,6,7]
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