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Ocean acidification slows retinal function in a damselfish through interference with GABA(A) receptors



Vision is one of the most efficient senses used by animals to catch prey and avoid predators. Therefore, any deficiency in the visual system could have important consequences for individual performance. We examined the effect of CO2 levels projected to occur by the end of this century on retinal responses in a damselfish, by determining the threshold of its flicker electroretinogram (fERG). The maximal flicker frequency of the retina was reduced by continuous exposure to elevated CO2, potentially impairing the capacity of fish to react to fast events. This effect was rapidly counteracted by treatment with a GABA antagonist (gabazine), indicating that GABAA receptor function is disrupted by elevated CO2. In addition to demonstrating the effects of elevated CO2 on fast flicker fusion of marine fishes, our results show that the fish retina could be a model system to study the effects of high CO2 on neural processing.
The Journal of Experimental Biology
© 2014. Published by The Company of Biologists Ltd | The Journal of Experimental Biology (2014) 217, 323-326 doi:10.1242/jeb.092478
Vision is one of the most efficient senses used by animals to catch
prey and avoid predators. Therefore, any deficiency in the visual
system could have important consequences for individual
performance. We examined the effect of CO2levels projected to
occur by the end of this century on retinal responses in a damselfish,
by determining the threshold of its flicker electroretinogram (fERG).
The maximal flicker frequency of the retina was reduced by
continuous exposure to elevated CO2, potentially impairing the
capacity of fish to react to fast events. This effect was rapidly
counteracted by treatment with a GABA antagonist (gabazine),
indicating that GABAAreceptor function is disrupted by elevated CO2.
In addition to demonstrating the effects of elevated CO2on fast flicker
fusion of marine fishes, our results show that the fish retina could be
a model system to study the effects of high CO2on neural
KEY WORDS: Flicker fusion frequency, Electroretinogram, Carbon
dioxide, Vision, Coral reef
CO2levels in the surface ocean are rising in line with rising
atmospheric CO2(Doney, 2010). It has recently been shown that
projected near-future CO2levels can impair sensory systems and
alter the behaviour of marine fishes (Munday et al., 2009; Munday
et al., 2012; Jutfelt et al., 2013). Behavioural changes include
increased boldness and activity (Munday et al., 2010; Munday et al.,
2013; Jutfelt et al., 2013), loss of behavioural lateralization
(Domenici et al., 2012; Jutfelt et al., 2013), altered auditory
preferences (Simpson et al., 2011) and impaired olfactory function
(Munday et al., 2009; Dixson et al., 2010; Ferrari et al., 2011). The
underlying reason for sensory impairment and behavioural changes
in fish exposed to elevated CO2appears to be a disruption to
neurotransmitter function, probably caused by changes to ion
gradients over neuronal membranes (Nilsson et al., 2012). Fish
regulate acid–base relevant ions, primarily bicarbonate (HCO3) and
chloride (Cl), to maintain blood and tissue pH when exposed to
high CO2(Ishimatsu et al., 2008). Experimental evidence suggests
that this leads to a disruption of GABAAreceptors, which are Cl
and HCO3channels gated by the neurotransmitter GABA (gamma-
amino butyric acid). Indeed, the sensory and behavioural alterations
caused by high-CO2exposure are virtually abolished by a moderate
1Queensland Brain Institute, University of Queensland, Brisbane 4072, Australia.
2ARC Centre of Excellence for Coral Reef Studies, James Cook University,
Townsville, QLD 4811, Australia. 3School of Marine and Tropical Biology, James
Cook University, Townsville, QLD 4811, Australia. 4Depar tment of Biosciences,
University of Oslo, Oslo 0316, Norway.
*Author for correspondence (
Received 14 June 2013; Accepted 23 September 2013
dose of the GABAAreceptor blocker gabazine (Nilsson et al., 2012).
Normally, GABAAreceptors act by hyperpolarizing neuronal
membranes due to the inflow of Cl, causing neuronal inhibition. It
has been hypothesized that during high-CO2exposure, the
transmembrane gradients of Cland HCO3are altered in some
neurons, thereby affecting GABAAfunction. Given the ubiquity of
GABAAreceptors in animal nervous systems, it is likely that
exposure to elevated CO2could affect a wide variety of behavioural
functions and activities in marine organisms.
To date, research on sensory impairment of fishes at elevated CO2
levels has concentrated mainly on the effects to olfactory
discrimination (e.g. Munday et al., 2009; Dixson et al., 2010; Ferrari
et al., 2011), and to some extent on auditory preferences (Simpson
et al., 2011). Recently, Ferrari and colleagues (Ferrari et al., 2012)
found that visual risk assessment was altered in juvenile fish
exposed to 850 μatm CO2. When presented with the sight of a large
novel reef fish, of sufficient size to be a predator, juvenile
damselfish that had been reared at high CO2exhibited reduced
antipredator responses and lacked the typical signalling behaviour
(bobbing) seen in juvenile damselfishes exposed to a threatening
situation (Ferrari et al., 2012). This suggests that the function of the
visual system is affected by high CO2. Such alterations to vision-
mediated behaviour could involve processing at the retinal level or
in higher brain centres.
In this study, we focused on the possibility that visual function at
the retinal level is affected by high-CO2exposure. The rapidity of
the response of animals to visual stimuli may be correlated with fast
flicker fusion (FFF). A visual system viewing a flickering light
source has a critical flicker fusion (CFF) threshold, above which the
flicker becomes too fast for the system to follow (Fritsches et al.,
2005), and the light appears continuous to the animal, and not
flashing. The CFF threshold varies between animals, and is often
related to lifestyle and illumination level, being fast in rapidly
moving organisms in bright light and slow in nocturnal slow-movers
(Horodysky et al., 2008; Smolka et al., 2013). It is therefore likely
that reduced CFF could impair the capacity to react to fast events
such as prey capture and predator avoidance.
Here we examined the effect of elevated CO2on retinal function
in the spiny damselfish, Acanthochromis polyacanthus (Bleeker
1855) by determining the CFF threshold of its electroretinogram
(ERG). This method records the electrical light response of the
retina using a non-invasive electrode placed on the eye. We show
that continuous exposure to the CO2level projected to occur in the
surface ocean by the end of this century (944 μatm) reduces the CFF
threshold (i.e. reduces the speed of the light response) and that this
effect can be effectively counteracted by gabazine treatment,
indicating an involvement of GABAAreceptor function.
The CFF of damselfish exposed to elevated CO2(78.6±3.9Hz, mean
± s.e.m.) was significantly decreased compared with that of the
Ocean acidification slows retinal function in a damselfish through
interference with GABAAreceptors
Wen-Sung Chung1, N. Justin Marshall1, Sue-Ann Watson2,3, Philip L. Munday2,3 and Göran E. Nilsson4,*
The Journal of Experimental Biology
control group (89.0±1.6Hz) (t10=5.28, P<0.0004). There was a
significant interaction between time interval and CO2treatment in
gabazine-treated fish (F4,20=35.64, P<0.0001). The CFF values of
fish from the elevated-CO2group were significantly less than those
of fish from the control group at 0, 5 and 10min; however, the value
increased through time to reach approximately the same level as the
control group after 15–20min (Fig. 1). The CFF of the control group
did not change significantly through time. There appeared to be a
slight increase in CFF of the control group after the first 5min, when
gabazine was first administered, but there was no further increase
through time, indicating that gabazine itself had negligible effect on
Our results show that the ability or the fish retina to react to fast
visual stimuli is reduced after exposure to CO2levels projected to
occur in the ocean by the end of this century. Moreover, the
underlying mechanism appears to involve altered GABAAreceptor
function, as the CFF threshold could be restored by treatment with
the GABAAreceptor antagonist gabazine, at a dose that has
previously been found to restore impaired olfactory preference and
lateralization in reef fish exposed to high CO2(Nilsson et al., 2012).
GABAAreceptors have been found to be intimately coupled to
retinal signal processing and direction selectivity at the ganglion cell
level, including the control of the fast flicker response in the fish
retina (Mora-Ferrer and Neumeyer, 2009). As GABAAreceptors
have been linked to neural dysfunction of high-CO2exposed fish, it
is not unexpected that retinal function is affected by elevated CO2
The CFF threshold of fish correlates with their lifestyle
(Horodysky et al., 2008) and a high CFF is likely to reflect the need
to react to fast events in their habitat, at the cost of reduced
performance at low light conditions. Pelagic fish CFF varies from
around 25Hz in species living in deeper water, to 80Hz in the
surface-dwelling yellow-fin tuna or the dolphin fish (Fritsches et al.,
2005). This fits well with the CFF of about 90Hz we found in A.
polyacanthus, which lives in a well-lit complex environment in close
proximity to predators.
Predatory events in the ocean may also be very rapid; it is therefore
of concern that spiny damselfish exposed to a near-future CO2level
slow their retinal response, with CFF dropping from around 90Hz to
less than 80Hz. This decrease in visual speed might result in reduced
reaction times, for example to a rapidly approaching predator, a
possibility supported by experiments showing that prey fish exposed
to similar levels of CO2to those used in our experiments have a
reduced perception and response to predation threat (Ferrari et al.,
2012; Allan et al., 2013). While behavioural responses to visual
stimuli may be different to those measured electrophysiologically at
the level of the retina, behavioural responses would probably be
slower than the initial physiological signal, and in the light of the
ubiquitous presence of GABAAreceptors in the nervous system, it is
possible that CO2exposure may lead to additional reductions in
reaction time due to disturbances at higher levels of neural processing
(Domenici et al., 2012).
Our results add to the increasing evidence that elevated CO2can
affect critical sensory processes in marine fishes and that the
underlying mechanism is associated with the function of GABAA
receptors. An important aspect of the present result is that the fish
retina could be used as a relatively simple model system to study the
effects of high CO2on neural processing. Indeed, isolated fish retina
preparations have long been used as models for neurophysiological
research (e.g. Hankins and Ruddock, 1984). A better understanding
of how and why high-CO2exposure affects GABAAreceptor
function, and possibly other neural components, would increase the
power to predict which physiological processes are likely to be
affected, and which organisms are most at risk, from future rises in
ocean CO2levels.
Animals and experimental treatments
Small A. polyacanthus, between 55 and 80mm standard length (SL), were
collected from the lagoon at Lizard Island (14°4008S; 145°2734E), Great
Barrier Reef, Australia, using barrier nets. Fish were distributed among eight
aquaria supplied with a constant flow of seawater at ambient summer
temperature (28–30°C) and fed to satiation twice daily with INVE
aquaculture pellets (Dendermonde, Belgium). Four of the aquaria were
supplied with seawater at present-day CO2levels (466 μatm) and four with
elevated CO2-equilibrated (944 μatm) seawater, as described below. The
elevated CO2treatment is consistent with projected CO2levels in the
atmosphere and surface ocean at year 2100 on a business-as-usual carbon
emissions trajectory (RCP 8.5) (Meinshausen et al., 2011). Fish were
maintained at control and elevated CO2for 6–7days prior to
experimentation, which is sufficient to induce the full range of sensory and
behavioural impairment in reef fish (Munday et al., 2010; Munday et al.,
2012; Ferrari et al., 2012). All animal care and experimental protocols
complied with ethics regulations of James Cook University and University
of Queensland.
Seawater manipulation
Elevated CO2levels were achieved by CO2-dosing seawater in a 60l header
tank to a set pHNBS (pH calibrated in National Bureau of Standards buffers)
to match the required CO2level. A pH controller (Aqua Medic GmbH,
Bissendorf, Germany) delivered CO2into a power-head pump at the bottom
of the header tank if the pH rose above the set point. Individual aquaria
received CO2-equilibrated seawater from the header tank at ~1000mlmin1.
The pHNBS of each aquarium was monitored regularly to ensure it remained
within ±0.05 of the desired level. Control aquaria received seawater from a
60l header tank diffused with ambient air. The temperature in each aquarium
was measured twice daily. Seawater total alkalinity and pHNBS for CO2
calculations were measured from replicate water samples of control and high
CO2water taken throughout the experiment. Total alkalinity was estimated
by Gran titration using certified reference materials (Dr A. Dickson, Scripps
Institution of Oceanography). Carbonate chemistry values are shown in
Table 1.
SHORT COMMUNICATION The Journal of Experimental Biology (2014) doi:10.1242/jeb.092478
CFF (Hz)
Time (min)
** ** *
0 5 10 15 20
Fig.1. The suppressed critical flicker fusion (CFF) threshold in
elevated-CO2treated fish is restored by gabazine treatment. Graph
shows CFF of control (triangles) and elevated-CO2(squares) treated
Acanthochromis polyacanthus. Gabazine was introduced into the respiratory
water of both groups at time zero. The CFF of the control group was
unaffected by gabazine, resulting in a stable phase at 93.5±1.4Hz. The
resolution of the high-CO2fishes recovered to the control level after 15min of
gabazine treatment. Student’s t-test, *P<0.05, **P<0.01. Error bars are s.e.m.
The Journal of Experimental Biology
Flicker ERG (fERG) was used to test the temporal visual resolution of
control and elevated-CO2-exposed fish (SL 63.0±3.4mm, mean ± s.d.). Fish
that had been in experimental treatments for 6–7days were anaesthetized
using 20ppm clove oil and pithed prior to the fERG measurement. ERGs
were recorded from the pithed fish, which was restrained in a horizontal
position on a sponge attached to a plastic board and held firmly in place
using silicone bandages. The fish was placed in a seawater bath maintained
at 29±1°C. Moistened tissue paper was placed on the upper side of the fish
and only one eye was exposed into the air for ERG recording, as described
below. Fish were maintained with constant gill irrigation using seawater at
the same CO2level as their experimental treatment (control or elevated CO2)
flowing at 0.1lmin1. Five elevated CO2individuals and five control
individuals were tested.
A second experiment tested the potential role of GABAAreceptors in the
temporal visual resolution of high-CO2-exposed fish. The procedure
described above was used, except control and high-CO2-exposed damselfish
(SL 74.3±5.8mm) were treated with gabazine (Sigma Chemical Co., St
Louis, MO, USA) throughout the fERG procedure. Gabazine is a fast-acting
and highly selective antagonist to the GABAAreceptor (Ueno et al., 1997).
From the start of the measurements the fish were ventilated with seawater
containing 4mgl1gabazine at a flow rate of 0.1lmin1. The visual
resolution of fish from the two treatment groups was tested with fERG every
5min for a total of 20min. Five individuals from the elevated-CO2group
and three control individuals were tested in this experiment.
ERG setup
A white LED lamp was placed 30cm above the test eye. The LED was
connected to a PowerLab ML 866 module (ADinstruments, Colorado
Springs, CO, USA) from which stimulus presentations were controlled by
the built-in functional generator to produce flickering stimuli (30 square
pulses) using the software LabChart Pro 7 (v7.2.5; ADinstruments). Each
pulse possessed 5ms power-on duration, rendering a constant photon flux
per flash. The irradiance of the lamp was calibrated with a USB4000
spectrometer (Ocean Optics, Dunedin, FL, USA). The light intensity was
controlled to emit 1014 photonscm2ms1. Teflon-coated chlorided 0.5mm
silver wire (Ag–AgCl2) electrodes were used to record the whole-eyeball
corneal ERGs. The recording electrode was placed on the corneal surface so
that it had contact at the edge of the pupil. The reference electrode was
placed on fatty tissue inside the orbit. Liquid conductive gel (EcoGel 200,
Mississauga, ON, Canada) was added to the tip of the recording electrode.
The system was grounded to the water of the experimental chamber. ERG
signals were amplified with a DP301 amplifier (Warner Instruments,
Hamden, CT, USA) using a 1000 gain passed through a 1Hz high-pass and
1kHz low-pass filter. The amplified ERG signals were further filtered with
the software’s electronic notch filter to remove periodic electrical noise
using LabChart Pro 7 with the Powerlab ML 866 module. The sampling
frequency was set at 4kHz.
Electrophysiological procedure
The electrical response of the whole eye was measured as the frequency of
a flickering light was increased. The threshold of the FFF was determined
by a standardized method (Fritsches et al., 2005), and in physiological terms
is when the eye’s response no longer follows the modulation of the light
(supplementary material Fig.S1). Measurements were carried out during the
daytime on light-adapted fish immobilized as described elsewhere
(Horodysky et al., 2008).
The flicker rate was started at 10Hz and the flash frequency gradually
increased until CFF. CFF is defined as the point where the modulated ERG
wavelets are no longer following the flickering light. The flickering stimuli
were presented for 3–10s (depending on the number and length of sweeps
used). Data were recorded across 30–100 sweeps for every flicker rate. Two
methods were used to determine the CFF threshold. First, the ERG waveforms
were visually inspected to determine whether they remained in phase with the
flickering stimuli. This process was restricted to the lower frequency test (less
than 65Hz). When the flicker frequency approached the CFF threshold, visual
inspection was insufficient to determine whether the wavelets remained in
phase with the flickering light. The CFF threshold was therefore determined
by analysing the power spectrum as described by Fritsches and colleagues
(Fritsches et al., 2005). The power at the stimulus frequency was compared
with the standard deviation of the power of a neighbouring frequency section.
The criterion for CFF was defined as the highest frequency (tested in 1Hz
steps) at which the power of the signal was at least five times larger than the
power of the noise. At higher frequencies the power of the response signal was
indistinct compared with the power of the noise.
A t-test was used to determine whether CFF values differed between control
fish and those in the elevated-CO2group. Repeated measures ANOVA was
used to compare CFF values of individuals in the elevated CO2group
against the control group over the 20min duration of the gabazine
experiment. Dunn’s multiple comparisons were then used to test the time
intervals at which the mean CFF of the two groups differed.
We thank Lizard Island Research Station for excellent logistical support.
Competing interests
The authors declare no competing financial interests.
Author contributions
The study was conceived and designed by P.L.M., N.J.M. and G.E.N. Experiments
and measurements were executed by W.-S.C., G.E.N., S.-A.W. and P.L.M. All
authors participated in the analysis, interpretation and writing process.
This research was financed by the Australian Research Council (to P.L.M. and
N.J.M.), the ARC Centre of Excellence for Coral Reef Studies (to P.L.M.) and the
University of Oslo (to G.E.N.).
Supplementary material
Supplementary material available online at
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Table1. Seawater carbonate chemistry parameters for control and elevated CO
Treatment Temperature (°C) Salinity pHNBS Total alkalinity (µmol kg1SW) pCO2(µatm)
Control 29.6±0.1 34.5 8.13±0.01 2269±9 466±15
High CO229.6±0.1 34.5 7.87±0.01 2257±4 944±19
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SHORT COMMUNICATION The Journal of Experimental Biology (2014) doi:10.1242/jeb.092478
... It appears that olfaction is not the only sense affected by ocean acidification, as vision is also impacted in fish, likely through the impairment of the functioning of the central nervous system (Chung et al., 2014) (see Section 2.2). Juvenile ambon damselfish (Pomacentrus amboinensis) under high CO 2 conditions (~850 μatm) did not display typical predator avoidance behaviour in response to a potential predator that the damselfish were only able to see, but could not smell (Ferrari et al., 2012). ...
... Juvenile ambon damselfish (Pomacentrus amboinensis) under high CO 2 conditions (~850 μatm) did not display typical predator avoidance behaviour in response to a potential predator that the damselfish were only able to see, but could not smell (Ferrari et al., 2012). Moreover, projected end of century levels of CO 2 was found to reduce the maximal flicker frequency of the retinal neurons of a species of damselfish (Acanthochromis polyacanthus; Chung et al., 2014). This could impair the ability of the fish to respond to fast moving objects, such as predatory fish (Chung et al., 2014). ...
... Moreover, projected end of century levels of CO 2 was found to reduce the maximal flicker frequency of the retinal neurons of a species of damselfish (Acanthochromis polyacanthus; Chung et al., 2014). This could impair the ability of the fish to respond to fast moving objects, such as predatory fish (Chung et al., 2014). ...
Climate change is a growing global issue with many countries and institutions declaring a climate state of emergency. Excess CO2 from anthropogenic sources and changes in land use practices are contributing to many detrimental changes, including increased global temperatures, ocean acidification and hypoxic zones along coastal habitats. All senses are important for aquatic animals, as it is how they can perceive and respond to their environment. Some of these environmental challenges have been shown to impair their sensory systems, including the olfactory, visual, and auditory systems. While most of the research is focused on how ocean acidification affects olfaction, there is also evidence that it negatively affects vision and hearing. The effects that temperature and hypoxia have on the senses have also been investigated, but to a much lesser extent in comparison to ocean acidification. This review assembles the known information on how these anthropogenic challenges affect the sensory systems of fishes, but also highlights what gaps in knowledge remain with suggestions for immediate action. Olfaction, vision, otolith, pH, freshwater, seawater, marine, central nervous system, electrophysiology, mechanism.
... The hypothesis for a reversal of GABA A receptor function, following exposure to elevated pCO 2 , has been proposed for marine fishes such as the Californian rockfish S. diploproa, zebrafish Danio rerio, damselfish Acanthochromis polyacanthus, and clownfish Amphiprion percula 16,60,64,65 and for the marine mollusc G. gibberulus and the bivalve M. arenaria. 33,66 In these studies, administration of GABA A agonist and antagonist was used to determine the role of the GABA A receptor in the observed behavioral changes. ...
Biological burrowing behavior is an important driver shaping ecosystems that is being threatened by CO2-induced ocean acidification; however, the effects of ocean acidification on burrowing behavior and its neurological mechanism remain unclear. This study showed that elevated pCO2 significantly affected the burrowing behaviors of the Manila clam Ruditapes philippinarum, such as increased foot contraction, burrowing time, and intrabottom movement and decreased burrowing depth. Delving deeper into the mechanism, exposure to elevated pCO2 significantly decreased extracellular pH and increased [HCO3-]. Moreover, an indicator GABAA receptor, a neuroinhibitor for movement, was found to be closely associated with behavioral changes. In situ hybridization confirmed that the GABAA receptor was widely distributed in ganglia and foot muscles, and elevated pCO2 significantly increased the mRNA level and GABA concentration. However, the increase in GABAA receptor and its ligand did not suppress the foot movement, but rather sent "excitatory" signals for foot contraction. The destabilization of acid-base homeostasis was demonstrated to induce an increase in the reversal potential for GABAA receptor and an alteration in GABAA receptor function under elevated pCO2. This study revealed that elevated pCO2 affects the burrowing behavior of Manila clams by altering GABAA receptor function from inhibitory to excitatory.
... These changes in ocean CO 2 partial pressure (pCO 2 ) are known to impact multiple taxa, including invertebrates and fish (Cattano et al., 2018;Melzner et al., 2020;Rosa et al., 2017). Moreover, previous studies identified that ocean acidification could directly impact fish behaviour (Goldenberg et al., 2018;Munday et al., 2019;, cognition (Ferrari et al., 2014;Paula, Baptista, et al., 2019) and disrupt several sensory mechanisms such as hearing, vision and olfaction (Chung et al., 2014;Porteus et al., 2018;Rossi et al., 2016). These behavioural effects were observed after a period of high CO 2 exposure, and some were observed even when fish were subsequently tested in control water (Munday et al., 2016). ...
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Ocean acidification is considered to affect fish behaviour through the disruption of GABAergic neurotransmission in controlled laboratory conditions, but less is known of the GABAergic role on fish behavioural performance in the wild. Most coral reef fishes engage in complex cleaning interactions, where they benefit from ectoparasite removal and stress relief. Here, we tested whether potential ocean acidification impairment of wild cleaning interactions, between the cleaner fish Labroides dimidiatus and its clients, can be explained by the GABAAR model. We used, the GABAA receptor agonist (muscimol) and antagonist (gabazine) for the first time in the wild and tested their effects on cleaning behaviour in Moorea Island (French Polynesia) to address natural interactions and recovery capacity. After exposure to expected ocean acidification conditions, the proportion of time spent advertising cleaning services, a measure of motivation to interact, dropped significantly relative to controls. Furthermore, the GABAergic antagonist gabazine recovered most CO2-induced behavioural alterations to control levels, consistent with the GABAAR model of altered Cl⁻ flux in ocean acidification-exposed fish. However, muscimol treatment only produced the same behavioural alterations found with CO2 exposure in time spent advertising cleaning. Our results support the evidence that ocean acidification alters some components of cleaning behaviour through GABAA receptor modulation with potential cascading effects on coral reef health and structure.
... polyacanthus) exposed to elevated pCO 2 . Even vision is related to GABA-A receptor function, as the negative effects of elevated pCO 2 exposure on A. polyacanthus retinal function-where impairments could preclude a fish's capacity to quickly respond to threatening events-can be counteracted upon exposure to a GABA antagonist (Chung et al., 2014). Also, the effects of elevated pCO 2 on fish behavior and sensory abilities occur when fish are exposed to levels >600 μatm pCO 2 , which is well within climate change relevant ocean acidification levels for the 21st century . ...
Coral reef fishes and the ecosystems they support represent some of the most biodiverse and productive ecosystems on the planet yet are under threat as they face dramatic increases in multiple, interacting stressors that are largely intensified by anthropogenic influences, such as climate change. Coral reef fishes have been the topic of 875 studies between 1979 and 2020 examining physiological responses to various abiotic and biotic stressors. Here, we highlight the current state of knowledge regarding coral reef fishes' responses to eight key abiotic stressors (i.e., pollutants, temperature, hypoxia and ocean deoxygenation, pH/CO2, noise, salinity, pressure/depth, and turbidity) and four key biotic stressors (i.e., prey abundance, predator threats, parasites, and disease) and discuss stressors that have been examined in combination. We conclude with a horizon scan to discuss acclimation and adaptation, technological advances, knowledge gaps, and the future of physiological research on coral reef fishes. As we proceed through this new epoch, the Anthropocene, it is critical that the scientific and general communities work to recognize the issues that various habitats and ecosystems, such as coral reefs and the fishes that depend on and support them, are facing so that mitigation strategies can be implemented to protect biodiversity and ecosystem health.
... Other sensorial impairments involving auditory and visual systems due to increased CO 2 levels have been also observed (e.g. Chung et al., 2014;Ferrari et al., 2010Ferrari et al., , 2012Simpson et al., 2011;Radford et al., 2021;Rossi et al., 2016Rossi et al., , 2018. In addition, some studies documented altered lateralization in fish exposed in the short-term to elevated CO 2 concentrations (Domenici et al., 2012;Näslund et al., 2015), or increased activity levels and boldness leading prey venturing further from shelters heedless of the predator presence (Cattano et al., 2019;Munday et al., 2013). ...
An in situ reciprocal transplant experiment was carried around a volcanic CO2 vent to evaluate the anti-predator responses of an anemone goby species exposed to ambient (∼380 μatm) and high (∼850 μatm) CO2 sites. Overall, the anemone gobies displayed largely unaffected behaviors under high-CO2 conditions suggesting an adaptive potential of Gobius incognitus to ocean acidification (OA) conditions. This is also supported by its 3-fold higher density recorded in the field under high CO2. However, while fish exposed to ambient conditions showed an expected reduction in the swimming activity in the proximity of the predator between the pre- and post-exposure period, no such changes were detected in any of the other treatments where fish experienced acute and long-term high CO2. This may suggest an OA effect on the goby antipredator strategy. Our findings contribute to the ongoing debate over the need for realistic predictions of the impacts of expected increased CO2 concentration on fish, providing evidence from a natural high CO2 system.
... Given their efficient capacity for maintaining acid-base homeostasis, fishes have long been considered to be robust organisms capable of tolerating OA [10][11][12][13]. However, reported indirect impacts of OA include both inter-and intraspecific changes in sensory behaviours [14], which result from directly altered neurosensory systems [15][16][17][18][19][20][21][22][23] that ultimately affect reproduction, fitness and mortality [24][25][26][27]. Although such effects are complex and vary with both biological traits and methods employed [28], sensory behavioural alterations induced by acid-base regulation are generally explained as a GABAergic system dysfunction due to an inversion of the Cl − /HCO 3 − channels across neuronal membranes [24,29]. ...
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Background Progressive CO2-induced ocean acidification (OA) impacts marine life in ways that are difficult to predict but are likely to become exacerbated over generations. Although marine fishes can balance acid–base homeostasis efficiently, indirect ionic regulation that alter neurosensory systems can result in behavioural abnormalities. In marine invertebrates, OA can also affect immune system function, but whether this is the case in marine fishes is not fully understood. Farmed fish are highly susceptible to disease outbreak, yet strategies for overcoming such threats in the wake of OA are wanting. Here, we exposed two generations of the European sea bass (Dicentrarchus labrax) to end-of-century predicted pH levels (IPCC RCP8.5), with parents (F1) being exposed for four years and their offspring (F2) for 18 months. Our design included a transcriptomic analysis of the olfactory rosette (collected from the F2) and a viral challenge (exposing F2 to betanodavirus) where we assessed survival rates. Results We discovered transcriptomic trade-offs in both sensory and immune systems after long-term transgenerational exposure to OA. Specifically, RNA-Seq analysis of the olfactory rosette, the peripheral olfactory organ, from 18-months-old F2 revealed extensive regulation in genes involved in ion transport and neuronal signalling, including GABAergic signalling. We also detected OA-induced up-regulation of genes associated with odour transduction, synaptic plasticity, neuron excitability and wiring and down-regulation of genes involved in energy metabolism. Furthermore, OA-exposure induced up-regulation of genes involved in innate antiviral immunity (pathogen recognition receptors and interferon-stimulated genes) in combination with down-regulation of the protein biosynthetic machinery. Consistently, OA-exposed F2 challenged with betanodavirus, which causes damage to the nervous system of marine fish, had acquired improved resistance. Conclusion F2 exposed to long-term transgenerational OA acclimation showed superior viral resistance, though as their metabolic and odour transduction programs were altered, odour-mediated behaviours might be consequently impacted. Although it is difficult to unveil how long-term OA impacts propagated between generations, our results reveal that, across generations, trade-offs in plastic responses is a core feature of the olfactory epithelium transcriptome in OA-exposed F2 offspring, and will have important consequences for how cultured and wild fish interacts with its environment.
... The dependence of reef fish on environmental colors for camouflage also means that coral bleaching has resulted in less cover for many of these species (Kaplan 2009). Water pollution causing increase turbidity has led to selective increase in fish that are more able to adapt to turbid waters (Schmidt 2001), while chemical pollution has been shown to cause ophthalmological impairments such as reduced retinal response capacity due to disruption of GABA receptor function in acidified water (Chung et al. 2014). ...
Three extant classes of vertebrates are considered under the larger umbrella of fish: Agnatha (Chap. 3), Chondrichthyes (Chap. 4), and Osteichthyes. As previously discussed in Chap. 3, the two surviving groups of Agnathans, lampreys and hagfish, are rarely encountered in veterinary medicine. Also discussed, Chondrichthyes are notable for having skeletons comprised of cartilage rather than bone. One of the two extant subclasses of Chondrichthyes, Elasmobranchii, is common throughout veterinary literature and aquatic medicine practice and includes sharks, rays, and skates (the subclass Holocephalii includes chimeras, which are not commonly encountered in clinical practice). However, most exotic animal practitioners and many will encounter fish in the third and largest class: Osteichthyes, which includes teleosts. Over 27,000 species within nearly 450 families of teleost or ‘truly bony’ fish have been described.
... Third, cross-disciplinary integration can be problematic when researchers apply methods and techniques from many different fields to test hypotheses without involving experts from each field or using methodological best practices. For example, research examining the effects of OA on fish behaviour (particularly in coral reef fishes) spans multiple disciplines including behavioural ecology (Munday et al., 2014a;Welch et al., 2014), ecophysiology (Laubenstein et al., 2019;Munday et al., 2009a), sensory biology (Chung et al., 2014;Ferrari et al., 2012;Munday et al., 2009b), neurobiology (Chivers et al., 2014;Heuer et al., 2016;Schunter et al., 2019), chemical ecology Ferrari et al., 2011) and molecular biology (Schunter et al., 2018;Tsang et al., 2020). Thus, the potential for cross-disciplinary integration in this field is considerable, with researchers having worked to gain a broad understanding of OArelated patterns and mechanisms. ...
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In a recent editorial, the Editors-in-Chief of Journal of Experimental Biology argued that consensus building, data sharing, and better integration across disciplines are needed to address the urgent scientific challenges posed by climate change. We agree and expand on the importance of cross-disciplinary integration and transparency to improve consensus building and advance climate change research in experimental biology. We investigated reproducible research practices in experimental biology through a review of open data and analysis code associated with empirical studies on three debated paradigms and for unrelated studies published in leading journals in comparative physiology and behavioural ecology over the last 10 years. Nineteen per cent of studies on the three paradigms had open data, and 3.2% had open code. Similarly, 12.1% of studies in the journals we examined had open data, and 3.1% had open code. Previous research indicates that only 50% of shared datasets are complete and re-usable, suggesting that fewer than 10% of studies in experimental biology have usable open data. Encouragingly, our results indicate that reproducible research practices are increasing over time, with data sharing rates in some journals reaching 75% in recent years. Rigorous empirical research in experimental biology is key to understanding the mechanisms by which climate change affects organisms, and ultimately promotes evidence-based conservation policy and practice. We argue that a greater adoption of open science practices, with a particular focus on FAIR (Findable, Accessible, Interoperable, Re-usable) data and code, represents a much-needed paradigm shift towards improved transparency, cross-disciplinary integration, and consensus building to maximize the contributions of experimental biologists in addressing the impacts of environmental change on living organisms.
The cuttlefish (Sepiella inermis) is an economically important species in the coastal seas of China. The impacts of ocean acidification on the ability of juvenile cuttlefish to select a suitable habitat, its hunting and swimming behavior, remains unknown. We examined behavior-related responses and the eye and cuttlebone structure of juvenile cuttlefish following short-term exposure to CO2-enriched seawater. The predation success rate decreased with the elevation in CO2 concentration. In the CO2 treatment groups, cuttlefish spent more time in the dark zone and the average swimming speed and total swimming distance significantly decreased. The structure of the retina and cuttlebone was affected by seawater acidification. Moreover, apoptotic cells were significantly increased in the eyes. In the wild, the impairment of the eye and cuttlebone may decrease the predation ability of juvenile cuttlefish and negatively affect their ability to select a suitable habitat, which would be detrimental to its population.
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Multibank retinas have rod photoreceptors stacked into multiple layers. They are found in many species of fish that inhabit dim environments and are one of the most common visual adaptations in the deep-sea. Despite its prevalence, the function of multibank retinas remained unknown. Two predominant theories, neither of which has been tested, have emerged: 1) they enhance sensitivity in dim light, and 2) they allow colour vision in dim light. To investigate the sensitivity hypothesis, we performed electrophysiological recordings and compared the rod pigments of three species of nocturnal reef fishes, two with a multibank retina ( Neoniphon sammara and Myripristis violacea ) and a control species with a single rod bank ( Ostorhinchus compressus ). Results indicated that nocturnal reef fishes with a multibank retina have higher temporal resolution of vision, as indicated by electrophysiology, and that their rhodopsin proteins likely also have faster retinal release kinetics, as suggested by amino acid substitutions. Electrophysiology also showed that the multibank retina conferred greater sensitivity to both dim and bright intensities than a single rod bank and this occurred at times when rod-derived signals usually dominate the visual response. This study provides the first functional evidence for enhanced dim-light sensitivity using a multibank retina while also suggesting novel roles for the adaptation in enhancing bright-light sensitivity and the speed of vision. Significance Most vertebrates have one layer of the dim-light active rod photoreceptors; however, some species have multiple layers, known as a multibank retina. We used electrophysiology on nocturnal reef fishes with and without multibank retinas to evaluate the sensory advantage of having multiple rod layers. We show that fish with multibank retinas have both faster vision and enhanced sensitivity to bright and dim light intensities. Thus, we resolve for the first time the function of multibank retinas – one of the most common visual adaptations in the deep sea. Our findings highlight an unconventional vertebrate visual system as well as the visual capabilities of fishes from the most vast (deep sea) and vibrant (reefs) ecosystems on the planet.
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We tested the effect of near-future CO2 levels (≈490, 570, 700, and 960 μatm CO2) on the olfactory responses and activity levels of juvenile coral trout, Plectropomus leopardus, a piscivorous reef fish that is also one of the most important fisheries species on the Great Barrier Reef, Australia. Juvenile coral trout reared for 4 weeks at 570 μatm CO2 exhibited similar sensory responses and behaviors to juveniles reared at 490 μatm CO2 (control). In contrast, juveniles reared at 700 and 960 μatm CO2 exhibited dramatically altered sensory function and behaviors. At these higher CO2 concentrations, juveniles became attracted to the odor of potential predators, as has been observed in other reef fishes. They were more active, spent less time in shelter, ventured further from shelter, and were bolder than fish reared at 490 or 570 μatm CO2. These results demonstrate that behavioral impairment of coral trout is unlikely if pCO2 remains below 600 μatm; however, at higher levels, there are significant impacts on juvenile performance that are likely to affect survival and energy budgets, with consequences for predator–prey interactions and commercial fisheries.
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As atmospheric CO<sub>2</sub> levels rise, the CO<sub>2</sub> concentration in ocean surface waters increases through a process commonly referred to as ocean acidification. Recently, surprising behavioural modifications has been detected in the early life stages of tropical coral reef fish exposed to ocean acidification-relevant CO<sub>2</sub> concentrations, but it has been unclear if this effect could occur in temperate waters. Here we show several severe behavioural disturbances, including effects on boldness, exploratory behaviour, lateralisation, and learning in a temperate fish, the three-spined stickleback ( Gasterosteus aculeatus ). The behavioural effects were consistent throughout the exposure period and increased in effect size with exposure time. We observed the effects on adult sticklebacks, a species known to be tolerant to other environmental stressors. Our findings suggest that behavioural abnormalities that stem from CO<sub>2</sub> exposure are not restricted to sensitive tropical species or early life stages and may therefore affect fish on a global scale. The severity of disturbances and the possibility of a serious behavioural problem for fish across the globe is cause for concern.
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Recent research has shown that exposure to elevated carbon dioxide (CO2) affects how fishes perceive their environment, affecting behavioral and cognitive processes leading to increased prey mortality. However, it is unclear if increased mortality results from changes in the dynamics of predator-prey interactions or due to prey increasing activity levels. Here we demonstrate that ocean pCO2 projected to occur by 2100 significantly effects the interactions of a predator-prey pair of common reef fish: the planktivorous damselfish Pomacentrus amboinensis and the piscivorous dottyback Pseudochromis fuscus. Prey exposed to elevated CO2 (880 µatm) or a present-day control (440 µatm) interacted with similarly exposed predators in a cross-factored design. Predators had the lowest capture success when exposed to elevated CO2 and interacting with prey exposed to present-day CO2. Prey exposed to elevated CO2 had reduced escape distances and longer reaction distances compared to prey exposed to present-day CO2 conditions, but this was dependent on whether the prey was paired with a CO2 exposed predator or not. This suggests that the dynamics of predator-prey interactions under future CO2 environments will depend on the extent to which the interacting species are affected and can adapt to the adverse effects of elevated CO2.
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Predator avoidance behaviour costs time, energy and opportunities, and prey animals need to balance these costs with the risk of predation. The necessary decisions to strike this balance are often based on information that is inherently imperfect and incomplete due to the limited sensory capabilities of prey animals. Our knowledge, however, about how prey animals solve the challenging task of restricting their responses to the most dangerous stimuli in their environment, is very limited. Using dummy predators, we examined the contribution of visual flicker to the predator avoidance response of the fiddler crab Uca vomeris. The results illustrate that crabs let purely black or purely white dummies approach significantly closer than black-and-white flickering dummies. We show that this effect complements other factors that modulate escape timing such as retinal speed and the crab's distance to its burrow, and is therefore not exclusively due to an earlier detection of the flickering signal. By combining and adjusting a range of imperfect response criteria in a way that relates to actual threats in their natural environment, prey animals may be able to measure risk and adjust their responses more efficiently - even under difficult or noisy sensory conditions.
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Average sea-surface temperature and the amount of CO(2) dissolved in the ocean are rising as a result of increasing concentrations of atmospheric CO(2). Many coral reef fishes appear to be living close to their thermal optimum, and for some of them, even relatively moderate increases in temperature (2-4°C) lead to significant reductions in aerobic scope. Reduced aerobic capacity could affect population sustainability because less energy can be devoted to feeding and reproduction. Coral reef fishes seem to have limited capacity to acclimate to elevated temperature as adults, but recent research shows that developmental and transgenerational plasticity occur, which might enable some species to adjust to rising ocean temperatures. Predicted increases in P(CO(2)), and associated ocean acidification, can also influence the aerobic scope of coral reef fishes, although there is considerable interspecific variation, with some species exhibiting a decline and others an increase in aerobic scope at near-future CO(2) levels. As with thermal effects, there are transgenerational changes in response to elevated CO(2) that could mitigate impacts of high CO(2) on the growth and survival of reef fishes. An unexpected discovery is that elevated CO(2) has a dramatic effect on a wide range of behaviours and sensory responses of reef fishes, with consequences for the timing of settlement, habitat selection, predator avoidance and individual fitness. The underlying physiological mechanism appears to be the interference of acid-base regulatory processes with brain neurotransmitter function. Differences in the sensitivity of species and populations to global warming and rising CO(2) have been identified that will lead to changes in fish community structure as the oceans warm and becomes more acidic; however, the prospect for acclimation and adaptation of populations to these threats also needs to be considered. Ultimately, it will be the capacity for species to adjust to environmental change over coming decades that will determine the impact of climate change on marine ecosystems.
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Predicted future CO 2 levels have been found to alter sensory responses and behaviour of marine fishes. Changes include increased boldness and activity, loss of behavioural lateralization, altered auditory preferences and impaired olfactory function. Impaired olfactory function makes larval fish attracted to odours they normally avoid, including ones from predators and unfavourable habitats. These behavioural alterations have significant effects on mortality that may have far-reaching implications for population replenishment, community structure and ecosystem function. However, the underlying mechanism linking high CO 2 to these diverse responses has been unknown. Here we show that abnormal olfactory preferences and loss of behavioural lateralization exhibited by two species of larval coral reef fish exposed to high CO 2 can be rapidly and effectively reversed by treatment with an antagonist of the GABA-A receptor. GABA-A is a major neurotransmitter receptor in the vertebrate brain. Thus, our results indicate that high CO 2 interferes with neurotransmitter function, a hitherto unrecognized threat to marine populations and ecosystems. Given the ubiquity and conserved function of GABA-A receptors, we predict that rising CO 2 levels could cause sensory and behavioural impairment in a wide range of marine species, especially those that tightly control their acid-base balance through regulatory changes in HCO 3- and Cl - levels.
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We present the greenhouse gas concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs). These projections include all major anthropogenic greenhouse gases and are a result of a multi-year effort to produce new scenarios for climate change research. We combine a suite of atmospheric concentration observations and emissions estimates for greenhouse gases (GHGs) through the historical period (1750–2005) with harmonized emissions projected by four different Integrated Assessment Models for 2005–2100. As concentrations are somewhat dependent on the future climate itself (due to climate feedbacks in the carbon and other gas cycles), we emulate median response characteristics of models assessed in the IPCC Fourth Assessment Report using the reduced-complexity carbon cycle climate model MAGICC6. Projected 'best-estimate' global-mean surface temperature increases (using inter alia a climate sensitivity of 3°C) range from 1.5°C by 2100 for the lowest of the four RCPs, called both RCP3-PD and RCP2.6, to 4.5°C for the highest one, RCP8.5, relative to pre-industrial levels. Beyond 2100, we present the ECPs that are simple extensions of the RCPs, based on the assumption of either smoothly stabilizing concentrations or constant emissions: For example, the lower RCP2.6 pathway represents a strong mitigation scenario and is extended by assuming constant emissions after 2100 (including net negative CO 2 emissions), leading to CO 2 concentrations returning to 360 ppm by 2300. We also present the GHG concentrations for one supplementary extension, which illustrates the stringent emissions implications of attempting to go back to ECP4.5 concentration levels by 2250 after emissions during the 21 st century followed the higher RCP6 scenario. Corresponding radiative forcing values are presented for the RCP and ECPs.
The apparent dissociation constants of carbonic acid in seawater were determined as functions of temperature (2-35°C) and salinity ( 19-43%) at atmospheric pressure by measurement of K'1 and the product K', K',. At 35sa salinity and 25°C the measured values were pE1 = 6.600 and pK'2 = 9.115; at 35% and 2°C the measured values were pK'1 = 6.177 and pKPz = 9.431.
1. With the global increase in CO 2 emissions, there is a pressing need for studies aimed at under-standing the effects of ocean acidification on marine ecosystems. Several studies have reported that exposure to CO 2 impairs chemosensory responses of juvenile coral reef fishes to predators. Moreover, one recent study pointed to impaired responses of reef fish to auditory cues that indi-cate risky locations. These studies suggest that altered behaviour following exposure to elevated CO 2 is caused by a systemic effect at the neural level. 2. The goal of our experiment was to test whether juvenile damselfish Pomacentrus amboinensis exposed to different levels of CO 2 would respond differently to a potential threat, the sight of a large novel coral reef fish, a spiny chromis, Acanthochromis polyancanthus, placed in a watertight bag. 3. Juvenile damselfish exposed to 440 (current day control), 550 or 700 latm CO 2 did not differ in their response to the chromis. However, fish exposed to 850 latm showed reduced antipreda-tor responses; they failed to show the same reduction in foraging, activity and area use in response to the chromis. Moreover, they moved closer to the chromis and lacked any bobbing behaviour typically displayed by juvenile damselfishes in threatening situations. 4. Our results are the first to suggest that response to visual cues of risk may be impaired by CO 2 and provide strong evidence that the multi-sensory effects of CO 2 may stem from systematic effects at the neural level.