Ocean acidification (OA) impacts the physiology of diverse marine taxa; among them corals that create complex reef framework structures. Biological processes operating on coral reef frameworks remain largely unknown from naturally high-carbon-dioxide (CO2) ecosystems. For the first time, we independently quantified the response of multiple functional groups instrumental in the construction and erosion of these frameworks (accretion, macroboring, microboring, and grazing) along natural OA gradients. We deployed blocks of dead coral skeleton for roughly 2 years at two reefs in Papua New Guinea, each experiencing volcanically enriched CO2, and employed high-resolution micro-computed tomography (micro-CT) to create three-dimensional models of changing skeletal structure. OA conditions were correlated with decreased calcification and increased macroboring, primarily by annelids, representing a group of bioeroders not previously known to respond to OA. Incubation of these blocks, using the alkalinity anomaly methodology, revealed a switch from net calcification to net dissolution at a pH of roughly 7.8, within Intergovernmental Panel on Climate Change’s (IPCC) predictions for global ocean waters by the end of the century. Together these data represent the first comprehensive experimental study of bioerosion and calcification from a naturally high-CO2 reef ecosystem, where the processes of accelerated erosion and depressed calcification have combined to alter the permanence of this essential framework habitat.
Archive for November, 2016
Enhanced macroboring and depressed calcification drive net dissolution at high-CO2 coral reefs
Published 18 November 2016 Science ClosedTags: algae, annelids, biological response, BRcommunity, calcification, chemistry, communityMF, corals, dissolution, field, light, mollusks, multiple factors, otherprocess, photosynthesis, respiration, South Pacific
Ocean acidification challenges copepod phenotypic plasticity (update)
Published 18 November 2016 Science ClosedTags: Baltic, biogeochemistry, biological response, crustaceans, field, mesocosms, morphology, physiology, reproduction, zooplankton
Ocean acidification is challenging phenotypic plasticity of individuals and populations. Calanoid copepods (zooplankton) are shown to be fairly plastic against altered pH conditions, and laboratory studies indicate that transgenerational effects are one mechanism behind this plasticity. We studied phenotypic plasticity of the copepod Acartia sp. in the course of a pelagic, large-volume mesocosm study that was conducted to investigate ecosystem and biogeochemical responses to ocean acidification. We measured copepod egg production rate, egg-hatching success, adult female size and adult female antioxidant capacity (ORAC) as a function of acidification (fCO2 ∼ 365–1231 µatm) and as a function of quantity and quality of their diet. We used an egg transplant experiment to reveal whether transgenerational effects can alleviate the possible negative effects of ocean acidification on offspring development. We found significant negative effects of ocean acidification on adult female size. In addition, we found signs of a possible threshold at high fCO2, above which adaptive maternal effects cannot alleviate the negative effects of acidification on egg-hatching and nauplii development. We did not find support for the hypothesis that insufficient food quantity (total particulate carbon < 55 µm) or quality (C : N) weakens the transgenerational effects. However, females with high-ORAC-produced eggs with high hatching success. Overall, these results indicate that Acartia sp. could be affected by projected near-future CO2 levels.
Continue reading ‘Ocean acidification challenges copepod phenotypic plasticity (update)’
Physiological responses of a population of Sargassum vulgare (Phaeophyceae) to high pCO2/low pH: implications for its long-term distribution
Published 17 November 2016 Science ClosedTags: abundance, algae, biological response, BRcommunity, field, Mediterranean, molecular biology, otherprocess, photosynthesis, physiology
Ocean Acidification (OA) is likely to affect macroalgal diversity in the future with species-specific responses shaping macroalgal communities. In this framework, it is important to focus research on the photosynthetic response of habitat-forming species which have an important structural and functional role in coastal ecosystems. Most of the studies on the impacts of OA involve short-term laboratory or micro/mesocosm experiments. It is more challenging to assess the adaptive responses of macroalgal community to decreasing ocean pH over long-term periods, as they represent the basis of trophic dynamics in marine environments. This work aims to study the physiological traits of a population of Sargassum vulgare that lives naturally in the high pCO2 vents system in Ischia (Italy), in order to predict the species behaviour in a possible OA future scenario. With this purpose, the photosynthetic performance of S. vulgare was studied in a wild, natural population living at low pH (6.7) as well as in a population transplanted from native (6.7) to ambient pH (8.1) for three weeks. The main results show that the photochemical activity and Rubisco expression decreased by 30% after transplanting, whereas the non-photochemical dissipation mechanisms and the photosynthetic pigment content increased by 50% and 40% respectively, in order to compensate for the decrease in photochemical efficiency at low pH. Our data indicated a stress condition for the S. vulgare population induced by pH variation, and therefore a reduced acclimation capability at different pH conditions. The decline of the PSII maximum quantum yield (Fv/Fm) and the increase of PARP enzyme activity in transplanted thalli further supported this hypothesis. The absence of the species at ambient pH conditions close to the vent system, as well as the differences in physiological traits, suggest a local adaptation of S. vulgare at pH 6.7, through optimization of photosynthetic performance.
Connecting pH with body size in the marine gastropod Trophon geversianus in a latitudinal gradient along the south-western Atlantic coast
Published 17 November 2016 Science ClosedTags: biological response, field, mollusks, morphology, South Atlantic
There is growing concern about the impact of contemporaneous ocean acidification on marine ecosystems, but strong evidence for predicting the consequences is still scant. We have used the gastropod Trophon geversianus as a study model for exploring the importance of oceanographic variables (sea surface temperature, chlorophyll a, oxygen, calcite and pH) on large-scale latitudinal variation in mean shell length and relative shell weight. Data were collected from a survey carried out in 34 sites along ~1600 km. Neither shell length nor relative shell weight showed any monotonic latitudinal trend, and the patterns of spatial variability were rather complex. After correcting for spatial autocorrelation, only pH showed a significant correlation with mean shell length and relative shell weight, but contrary to expectations, the association was negative in both cases. We hypothesize that this could mirror the negative effect of acidification on growth rate, which may cause larger asymptotic size. Latitudinal trends of body size variation are not easy to generalize using ecogeographic rules, and may be the result of a complex interaction of environmental drivers and life-history responses.
Chemical composition of two mineralogically contrasting Arctic bivalves’ shells and their relationships to environmental variables
Published 16 November 2016 Science ClosedTags: Arctic, biological response, calcification, chemistry, field, mollusks, morphology, otherprocess
The main goal of this study was to determine the concentrations of trace elements in the mineralogically contrasting shells of two Arctic bivalves: Chlamys islandica and Ciliatocardium ciliatum. Aragonite shells seem to be more susceptible to the binding of metal ions, which is most likely a result of their crystal lattice structure. We suggest that less biologically controlled aragonite mineralization tends to incorporate more metal impurities into the crystal lattice in waters with a lower pH, where metal ions are more available. Higher concentrations of impurities may further increase the lattice distortion causing lower crystal lattice stability and higher susceptibility to dissolution. Calcitic shells seem to be less prone to bind metal ions than aragonite shells most likely because under strict biological control, the uptake of ions from ambient seawater is more selective; thus, the final crystal lattice is less contaminated by other metals and is more resistant to dissolution.
Export of calcium carbonate corrosive waters from the East Siberian Sea
Published 16 November 2016 Science ClosedTags: Arctic, chemistry, field
The Siberian Shelf Seas are areas of extensive biogeochemical transformation of organic matter, both of marine and terrestrial origin. This in combination with brine production from sea ice formation results in a cold bottom water of relative high salinity and partial pressure of carbon dioxide (pCO2). Data from the SWERUS-C3 expedition compiled on the icebreaker Oden in July to September 2014 show the distribution of such waters at the outer shelf, as well as their export into the deep central Arctic basins. Very high pCO2 water, up to close to 1000 µatm, was observed associated with high nutrients and low oxygen concentrations. Consequently the saturation state of calcium carbonate was low, down to less than 0.8 for calcite and 0.5 for aragonite. Waters undersaturated in aragonite were also observed in the surface in waters at equilibrium with atmospheric CO2, however, at these conditions the cause of under-saturation was low salinity from river runoff and/or sea ice melt. The calcium carbonate corrosive water was observed all along the continental margin and well out into the deep Makarov and Canada Basins at a depth from about 50 m depth in the west to about 150 m in the east. These waters of low aragonite saturation state are traced in historic data to the Canada Basin and in the waters flowing out of the Arctic Ocean north of Greenland and in the western Fram Strait, thus potentially impacting the marine life in the North Atlantic Ocean.
Continue reading ‘Export of calcium carbonate corrosive waters from the East Siberian Sea’
The seasonal cycle of carbonate system processes in Ryder Bay, West Antarctic Peninsula
Published 16 November 2016 Science ClosedTags: Antarctic, biogeochemistry, biological response, BRcommunity, chemistry, field, respiration
The carbon cycle in seasonally sea-ice covered waters remains poorly understood due to both a lack of observational data and the complexity of the system. Here we present three consecutive seasonal cycles of upper ocean dissolved inorganic carbon (DIC) and total alkalinity measurements from Ryder Bay on the West Antarctic Peninsula. We attribute the observed changes in DIC to four processes: mixing of water masses, air-sea CO2 flux, calcium carbonate precipitation/dissolution and photosynthesis/respiration. This approach enables us to resolve the main drivers of the seasonal DIC cycle and also investigate the mechanisms behind interannual variability in the carbonate system. We observe a strong, asymmetric seasonal cycle in the carbonate system, driven by physical processes and primary production. In summer, melting glacial ice and sea ice and a reduction in mixing with deeper water reduce the concentration of DIC in surface waters. The dominant process affecting the carbonate system is net photosynthesis which reduces DIC and the fugacity of CO2, making the ocean a net sink of atmospheric CO2. In winter, mixing with deeper, carbon-rich water and net heterotrophy increase surface DIC concentrations, resulting in pH as low as 7.95 and aragonite saturation states close to 1. We observe no clear seasonal cycle of calcium carbonate precipitation/dissolution but some short-lived features of the carbonate time series strongly suggest that significant precipitation of calcium carbonate does occur in the Bay. The variability observed in this study demonstrates that changes in mixing and sea ice cover significantly affect carbon cycling in this dynamic environment. Maintaining this unique time series will allow the carbonate system in seasonally sea-ice covered waters to be better understood.
Contrasting effects of ocean acidification on coral reef “animal forests” versus seaweed “kelp forests”
Published 16 November 2016 Science ClosedTags: biological response, corals, multiple factors, nutrients, review, temperature
Ocean acidification is the sustained absorption of anthropogenically derived CO2 and is a major threat to marine ecosystems. Ocean acidification results in the decline of seawater pH (increase in protons) and carbonate ions and increased CO2. Added CO2 could benefit terrestrial forests, but changes in the concentration of any one of aspect of the carbonate system could affect various marine organisms both positively and negatively. One ecosystem under particular threat from ocean acidification is tropical coral reefs, formed predominately by scleractinian coral species that are predicted to be negatively impacted by ocean acidification. In contrast, temperate shallow rocky reefs are dominated by seaweed that forms extensive kelp/seaweed forests; these noncalcareous seaweeds are not predicted to be as negatively impacted by ocean acidification. Tropical coral reef “animal forests” and temperate “kelp forests” both provide three-dimensional habitat for tens of thousands of species, but are characterized by vastly different environmental regimes. The present chapter outlines differences in key environmental parameters (such as nutrients, water motion, and temperature) in these two habitats that could dictate the relative magnitudes of the effects of ocean acidification within them. The vulnerability of key habitat-forming organisms within these habitats and the potential mechanisms behind specific responses to ocean acidification are also discussed.
Resilience to ocean acidification: decreased carbonic anhydrase activity in sea anemones under high pCO2 conditions
Published 16 November 2016 Science ClosedTags: biological response, cnidaria, field, laboratory, Mediterranean, morphology, photosynthesis, physiology
Non-calcifying photosynthetic anthozoans have emerged as a group that may thrive under high carbon dioxide partial pressure ( pCO2) conditions via increased productivity. However, the physiological mechanisms underlying this potential success are unclear. Here we investigated the impact of high pCO2 on the dissolved inorganic carbon (DIC) use in the temperate sea anemone Anemonia viridis. We assessed the impacts of long-term exposure to high pCO2, i.e. sampling in situ natural CO2 vents (Vulcano, Italy), and short-term exposure, i.e. during a 3 wk controlled laboratory experiment. We focused on photo-physiological parameters (net photosynthesis rates, chlorophyll a content and Symbiodinium density) and on carbonic anhydrase (CA) activity, an enzyme involved in the energy-demanding process of DIC absorption. Long-term exposure to high pCO2 had no impact on Symbiodinium density and chlorophyll a content. In contrst, short-term exposure to high pCO2 induced a significant reduction in Symbiodinium density, which together with unchanged net photosynthesis resulted in the increase of Symbiodinium productivity per cell. Finally, in both in situ long-term and laboratory short-term exposure to high pCO2, we observed a significant decrease in the CA activity of sea anemones, suggesting a change in DIC use (i.e. from an HCO3- to a CO2 user). This change could enable a shift in the energy budget that may increase the ability of non-calcifying photosynthetic anthozoans to cope with ocean acidification.
A Call to Action from a member of a West Coast alliance in the United States of America says what climate change is doing to oceans; together with ocean acidification, it may have direct consequences if left unchecked.
Mr Jay Manning sounded the warning at a side event during the ongoing 22nd Conference of the Parties (COP 22) to the United Nations Framework Convention on Climate Change (UNFCCC) on November 10, in Marrakech, Morocco.
“In the States, for example, there was an incident where oyster hatcheries were wiped out due to rising acid levels triggered by increasing levels of carbon in the atmosphere,” he said.
He added: “However, unlike climate change, ocean acidification is not polarising the world as it is an issue that one can talk about and be given audience.”
Continue reading ‘Acidification poses threat to sea life (edited)’
TRACC is developing proposals (partners wanted) to create solutions to the acidification of coral reefs by climate change. We will take what is known from reef resilience to pH change and experimental coral planting methods around the world and to proactively prepare the groundwork for adaption strategies to identify and grow coral species capable of mitigating the impacts of increasing levels of Carbon Dioxide on the global ocean. The joint perspective, will also be studied where the combined effects of two or more stressors acting at the same time are investigated. The coral nursery resource developed will enable detailed laboratory studies and field experiments and encourage cross-disciplinary and international cooperative partnerships.
The scale of the problem is global and it will require significant funds (full GEF grant or a full Adaptation fund grant) to bring enough researchers together to be able to tackle ocean acidification. An important part of this strategic plan is to develop proposals for a major grant or other sources of funding to promote adaptations by reefs. To help a wide range of reef organisms adapt to changing pH in the sea it will be necessary to work with DNA and genes to select sub-populations that are better able to synthesize the reef building blocks in a more acid environment. The appropriate coral species, once identified, could then be looked at more closely in terms of their genetic make-up and genetic modification employed to increase resistance to acid conditions should that be seen as feasible.
Translating crustacean biological responses from CO2 bubbling experiments into population-level predictions
Published 15 November 2016 Science ClosedTags: abundance, biological response, BRcommunity, crustaceans, laboratory, methods, mortality, North Atlantic, otherprocess, performance
Many studies of animal responses to ocean acidification focus on uniformly conditioned age cohorts that lack complexities typically found in wild populations. These studies have become the primary data source for predicting higher level ecological effects, but the roles of intraspecific interactions in re-shaping biological, demographic and evolutionary responses are not commonly considered. To explore this problem, I assessed responses in the mysid Americamysis bahia to bubbling of CO2-enriched and un-enriched air into the seawater supply in flow-through aquariums. I conducted one experiment using isolated age cohorts and a separate experiment using intact populations. The seawater supply was continuously input from Narragansett Bay (Rhode Island, USA). The 28-day cohort study was maintained without resource or spatial limitations, whereas the 5-month population study consisted of stage-structured populations that were allowed to self-regulate. These differences are common features of experiments and were intentionally retained to demonstrate the effect of methodological approaches on perceptions of effect mechanisms. The CO2 treatment reduced neonate abundance in the cohort experiment (24% reduction due to a mean pH difference of −0.27) but not in the population experiment, where effects were small and were strongest for adult and stage 1 survival (3% change due to a mean pH difference of −0.25). I also found evidence of competition in the population experiment, further complicating relationships with cohort experiments. These results point to limitations of standard cohort tests. Such experiments should be complimented by studies of intact populations where responses may be affected by evolution, acclimation, and competition.
Calcareous nannofossils at the Triassic/Jurassic boundary: stratigraphic and paleoceanographic characterization
Published 15 November 2016 Science ClosedTags: paleo
In this work, calcareous nannofossils are identified for the first time in the uppermost Triassic sequence of the Lombardy Basin (Southern Calcareous Alps, Italy). Two zones are recognized, namely the NT2b (latest Triassic) and the NJT1 (earliest Jurassic). Two species resulted to be good markers to constrain the TJB interval: Prinsiosphaera triassica and Schizosphaerella punctulata. Nannofossil data are calibrated with C isotopic chemostratigraphy obtained for carbonate and organic matter. Size reduction of P. triassica and a decline in the abundance of Triassic nannofossils are detected soon after the “precursor Carbon Isotope Excursion (CIE) and culminated during the “initial negative CIE” characterized by lowest nannofossil abundances and small-sized P. triassica. The extinction of Triassic nannofossils occurred in distinctive steps within the “initial negative CIE”, while the Jurassic S. punctulata is first observed at the base of the “main negative CIE”. The latest Triassic nannofossil decline in abundance, size reduction and extinctions, represent a progressive deterioration associated to the Central Atlantic Magmatic Province (CAMP) volcanism. Our findings are consistent with nannofossil changes at supraregional scale and indicate that the massive CAMP flood basalts were preceded by initial volcanic pulses. We speculate that a combination of climate change, fertilization and ocean acidification started to influence the calcification process prior to the “initial negative CIE”. Nannoplankton extinctions were not simultaneous and might imply limited capacity for adaptation in the early stages of evolutionary history. However, originations of new taxa soon after the disappearance of Triassic forms suggest the ability to rapidly overcame extreme stressing conditions.
Biomineralization and global change: A new perspective for understanding the end-Permian extinction
Published 15 November 2016 Science ClosedTags: biological response, calcification, crustaceans, paleo
We investigated the kill mechanisms of the end-Permian mass extinction by analyzing patterns in biomineralization of marine invertebrates. The microstructures of Upper Permian brachiopod organocarbonate shells show the demise of the production of fabrics with a columnar layer—which has less organic matrix—in favor of more organic-rich shells at the end of Permian. Also, in the 100–120 k.y. interval prior to the Permian-Triassic boundary (PTB), the Rhynchonellata had small calcite structural units (fibers) and thus a higher shell organic content, whereas the Strophomenata were not able to produce smaller units. This suggests that the two classes had a different capacity to cope with environmental change, with the Rhynchonellata being more able to buffer against pH changes and surviving the PTB, whereas the Strophomenata became extinct. The observed trends in biomineralization are similar to the patterns in extant marine invertebrates exposed to increasing pCO2 and decreasing pH, indicating that ocean acidification could have been one of the kill mechanisms of the mass extinction at the PTB.
On the causes of mass extinctions
Published 15 November 2016 Science ClosedTags: methods, paleo, review
The temporal link between large igneous province (LIP) eruptions and at least half of the major extinctions of the Phanerozoic implies that large scale volcanism is the main driver of mass extinction. Here we review almost twenty biotic crises between the early Cambrian and end Cretaceous and explore potential causal mechanisms. Most extinctions are associated with global warming and proximal killers such as marine anoxia (including the Early/Middle Cambrian, the Late Ordovician, the intra-Silurian, intra-Devonian, end-Permian, and Early Jurassic crises). Many, but not all of these are accompanied by large negative carbon isotope excursions, supporting a volcanogenic origin. Most post-Silurian biocrises affected both terrestrial and marine biospheres, suggesting that atmospheric processes were crucial in driving global extinctions. Volcanogenic-atmospheric kill mechanisms include ocean acidification, toxic metal poisoning, acid rain, and ozone damage and consequent increased UV-B radiation, volcanic darkness, cooling and photosynthetic shutdown, each of which has been implicated in numerous events. Intriguingly, some of the most voluminous LIPs such as the oceanic plateaus of the Cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing LIP lethality. The missing link might be continental configuration because the best examples of the LIP/extinction relationship occurred during the time of Pangaea. Many of the proximal kill mechanisms in LIP/extinction scenarios are also potential effects of bolide impact, including cooling, warming, acidification and ozone destruction. However, the absence of convincing temporal links between impacts and extinctions other than the Chicxulub-Cretaceous example, suggests that impacts are not the main driver of extinctions. With numerous competing extinction scenarios, and the realisation that some of the purported environmental stresses may once again be driving mass extinction, we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises.
From Marrakech, where the winds of change also blow
Published 14 November 2016 Web sites and blogs ClosedA funny thing happened at a meeting this week in Marrakech. Countries from around the world are meeting to decide how they will implement the landmark Paris Climate Agreement. In December last year, 195 countries agreed to aggressive targets to reduce emissions of greenhouse gases and limit global warming. As the COP22 meeting began, our country, which has been a crucial player and leader in the fight against climate change, elected Donald J. Trump as President.
Continue reading ‘From Marrakech, where the winds of change also blow’
IAEA to inform COP22 participants on role of nuclear and isotopic techniques in climate action
Published 14 November 2016 Press releases ClosedThe IAEA is participating in the Morocco Climate Change Conference, also known as COP22, over the next two weeks, and will inform delegates about the contribution of nuclear and isotopic techniques to combating climate change. Nuclear techniques can be used to both mitigate and help adapt to the consequences of climate change.
Event will put focus on ocean acidification in Maine
Published 14 November 2016 Media coverage ClosedAUGUSTA, Maine — A group of environmentalists, academics and state leaders are hosting an event in the state’s capital city to discuss approaches to ocean pollution in Maine.
The event will be held at the State House Legislative Council Room in Augusta on Tuesday and will focus on ocean acidification.
Continue reading ‘Event will put focus on ocean acidification in Maine’
A review of climate change and the implementation of marine biodiversity legislation in the United Kingdom
Published 11 November 2016 Science ClosedTags: North Atlantic, policy, review
1. Marine legislation, the key means by which the conservation of marine biodiversity is achieved, has been developing since the 1960s. In recent decades, an increasing focus on ‘holistic’ policy development is evident, compared with earlier ‘piecemeal’ sectoral approaches. Important marine legislative tools being used in the United Kingdom, and internationally, include the designation of marine protected areas and the Marine Strategy Framework Directive (MSFD) with its aim of meeting ‘Good Environmental Status’ (GES) for European seas by 2020.
2. There is growing evidence of climate change impacts on marine biodiversity, which may compromise the effectiveness of any legislation intended to promote sustainable marine resource management.
3. A review of key marine biodiversity legislation relevant to the UK shows climate change was not considered in the drafting of much early legislation. Despite the huge increase in knowledge of climate change impacts in recent decades, legislation is still limited in how it takes these impacts into account. There is scope, however, to account for climate change in implementing much of the legislation through (a) existing references to environmental variability; (b) review cycles; and (c) secondary legislation and complementary policy development.
4. For legislation relating to marine protected areas (e.g. the EC Habitats and Birds Directives), climate change has generally not been considered in the site-designation process, or for ongoing management, with the exception of the Marine (Scotland) Act. Given that changing environmental conditions (e.g. rising temperatures and ocean acidification) directly affect the habitats and species that sites are designated for, how this legislation is used to protect marine biodiversity in a changing climate requires further consideration.
5. Accounting for climate change impacts on marine biodiversity in the development and implementation of legislation is vital to enable timely, adaptive management responses. Marine modelling can play an important role in informing management decisions.
Effects of elevated CO2 on predator avoidance behaviour by reef fishes is not altered by experimental test water
Published 11 November 2016 Science ClosedTags: biological response, fish, laboratory, methods, performance, South Pacific
Pioneering studies into the effects of elevated CO2 on the behaviour of reef fishes often tested high-CO2 reared fish using control water in the test arena. While subsequent studies using rearing treatment water (control or high CO2) in the test arena have confirmed the effects of high CO2 on a range of reef fish behaviours, a further investigation into the use of different test water in the experimental arena is warranted. Here, we used a fully factorial design to test the effect of rearing treatment water (control or high CO2) and experimental test water (control or high CO2) on antipredator responses of larval reef fishes. We tested antipredator behaviour in larval clownfish Amphiprion percula and ambon damselfish Pomacentrus amboinensis, two species that have been used in previous high CO2 experiments. Specifically, we tested if: (1) using control or high CO2 water in a two channel flume influenced the response of larval clownfish to predator odour; and (2) using control or high CO2 water in the test arena influenced the escape response of larval damselfish to a startle stimulus. Finally, (3) because the effects of high CO2 on fish behaviour appear to be caused by altered function of the GABA-A neurotransmitter we tested if antipredator behaviours were restored in clownfish treated with a GABA antagonist (gabazine) in high CO2 water. Larval clownfish reared from hatching in control water (496 µatm) strongly avoided predator cue whereas larval clownfish reared from hatching in high CO2 (1,022 µatm) were attracted to the predator cue, as has been reported in previous studies. There was no effect on fish responses of using either control or high CO2 water in the flume. Larval damselfish reared for four days in high CO2 (1,051 µatm) exhibited a slower response to a startle stimulus and slower escape speed compared with fish reared in control conditions (464 µatm). There was no effect of test water on escape responses. Treatment of high-CO2 reared clownfish with 4 mg l−1 gabazine in high CO2 seawater restored the normal response to predator odour, as has been previously reported with fish tested in control water. Our results show that using control water in the experimental trials did not influence the results of previous studies on antipredator behaviour of reef fishes and also supports the results of novel experiments conducted in natural reef habitat at ambient CO2 levels.
