The past, present and future of cleaner fish cognitive performance as a function of CO₂levels

Abstract

Ocean acidification is one of the many consequences of climate change. Various studies suggest that marine organisms' behaviour will be impaired under high CO 2 . Here, we show that the cognitive performance of the cleaner wrasse , Labroides dimidiatus , has not suffered from the increase of CO 2 from pre-industrial levels to today, and that the standing variation in CO 2 tolerance offers potential for adaptation to at least 750 µatm. We acclimated cleaners over 30 days to five levels of pCO 2, from pre-industrial to high future CO 2 scenarios, before testing them in an ecologically relevant task—the ability to learn to prioritize an ephemeral food source over a permanent one. Fish learning abilities remained stable from pre-industrial to present-day pCO 2 . While performance was reduced under mid (750 µatm) and high CO 2 (980 µatm) scenarios, under the former 36% of cleaners still solved the task. The presence of tolerant individuals reveals potential for adaptation, as long as selection pressure on cognitive performance is strong. However, the apparent absence of high CO 2 tolerant fish, and potentially synergistic effects between various climate change stressors, renders the probability of further adaptation unlikely.

Diel CO2 fluctuations alter the molecular response of coral reef fishes to ocean acidification conditions

“…Furthermore, behavioural impairment occur in a number of reef fishes species at this CO2 level (Devine, Munday, & Jones, 2012;Ferrari et al, 2011;Munday et al, 2010a;Welch et al, 2014). For instance, a coral reef cleaner wrasse exhibited variable effects of CO2 on learning behaviour at 750 µatm but impairment occurred in all individuals at 950 µatm (Paula, Baptista, et al, 2019), also suggesting 750 µatm to be a tipping point for behavioural impairment in reef fishes. The increase in CO2 level from to 750 initiated transcriptional responses in immediate early genes as well as genes involved in brain metabolism and neuronal development, but chloride or bicarbonate transporters did not change in expression.…”

“…Previous experiments indicate that behavioural abnormalities are first evident at around 700 µatm CO2, although the magnitude of effect is not as large as observed at higher CO2 levels (Ferrari et al, 2011;Jarrold et al, 2017;Munday et al, 2010b;Paula, Baptista, et al, 2019;Welch, Watson, Welsh, McCormick, & Munday, 2014). Therefore, the inclusion of the 750 and 750 ± 300 µatm CO2 treatments enabled us to determine how diel pCO2 cycles may affect the onset threshold of behavioural abnormalities and the molecular responses in the brains of fishes.…”

Diel pCO2 fluctuations alter the molecular response of coral reef fishes to ocean acidification conditions

“…However, the magnitude of pCO 2 fluctuations is predicted to increase at least three-fold by the year 2100 as OA leads to the reduced buffering capacity of seawater (McNeil & Matsumoto, 2019;McNeil & Sasse, 2016;Shaw et al, 2013) and thus the species used in this study could be exposed to daily fluctuations of between 150 and 450 µatm by the end of the century. Previous experiments indicate that behavioural abnormalities are first evident at around 700 µatm pCO 2 , although the magnitude of effect is not as large as observed at higher pCO 2 levels (Ferrari et al, 2011;Jarrold et al, 2017;Munday et al, 2010b;Paula, Baptista, et al, 2019;Welch et al, 2014). Therefore, the inclusion of the 750 and 750 ± 300 µatm pCO 2 treatments enabled us to determine how diel pCO 2 cycles may affect the onset threshold of behavioural abnormalities and the molecular responses in the brains of fishes.…”

Molecular basis of parental contributions to the behavioural tolerance of elevated pCO2in a coral reef fish

“…However, there is also individual variation in behavioural sensitivity to elevated CO 2 , with some individuals exhibiting impaired behaviours, whereas others do not, especially at CO 2 levels projected to occur in the ocean this century (i.e. approximately 700 µatm CO 2 ) [ 23 , 27 , 28 ]. Such individual variation could be the raw material for population-level adaptation to rising CO 2 levels [ 14 , 29 ].…”

“…The underlying cause of this behavioural change is thought to be impaired function of GABA A receptors (GABA is the major inhibitory neurotransmitter in the brain) caused by changes in the concentration of acid-base relevant ions to maintain pH homeostasis in a high CO 2 environment [17,[20][21][22]. Elevated CO 2 has also been demonstrated to affect learning ability, decision making, turning preference, auditory preferences, visual acuity, shoaling, boldness and escape responses in a range of different fish species [16,18,[23][24][25]. Such alterations in behaviour could affect individual performance and survivorship, with potential implications for community structure and population replenishment [8,26].…”