Posts Tagged 'fish'

Physiological resilience of pink salmon to naturally occurring ocean acidification

Pacific salmon stocks are in decline with climate change named as a contributing factor. The North Pacific coast of British Columbia is characterized by strong temporal and spatial heterogeneity in ocean conditions with upwelling events elevating CO2 levels up to 10-fold those of pre-industrial global averages. Early life stages of pink salmon have been shown to be affected by these CO2 levels, and juveniles naturally migrate through regions of high CO2 during the energetically costly phase of smoltification. To investigate the physiological response of out-migrating wild juvenile pink salmon to these naturally occurring elevated CO2 levels, we captured fish in Georgia Strait, British Columbia and transported them to a marine lab (Hakai Institute, Quadra Island) where fish were exposed to one of three CO2 levels (850, 1500 and 2000 μatm CO2) for 2 weeks. At ½, 1 and 2 weeks of exposure, we measured their weight and length to calculate condition factor (Fulton’s K), as well as haematocrit and plasma [Cl]. At each of these times, two additional stressors were imposed (hypoxia and temperature) to provide further insight into their physiological condition. Juvenile pink salmon were largely robust to elevated CO2 concentrations up to 2000 μatm CO2, with no mortality or change in condition factor over the 2-week exposure duration. After 1 week of exposure, temperature and hypoxia tolerance were significantly reduced in high CO2, an effect that did not persist to 2 weeks of exposure. Haematocrit was increased by 20% after 2 weeks in the CO2 treatments relative to the initial measurements, while plasma [Cl] was not significantly different. Taken together, these data indicate that juvenile pink salmon are quite resilient to naturally occurring high CO2 levels during their ocean outmigration.

Continue reading ‘Physiological resilience of pink salmon to naturally occurring ocean acidification’

An extreme decline effect in ocean acidification ecology

Ocean acidification – deceasing oceanic pH resulting from the uptake of excess atmospheric CO2 – is expected to affect marine life in the future. Among the possible consequences, a series of studies on coral reef fishes suggested that the direct effects of acidification on fish behaviour will be the most catastrophic. Recent studies documenting a lack of effect of experimental ocean acidification on fish behaviour, however, call this dire prediction into question. Here, we critically assess the past decade of ocean acidification research regarding direct effects on fish behaviour. Using a meta-analysis, we provide quantitative evidence that the research to date on this topic is strongly characterized by a phenomenon known as the “decline effect”, where large effects have all but disappeared over a decade. The decline effect in this field cannot be explained biologically, but is strongly associated with well-known biases to which the process of science is generally prone. We contend that ocean acidification does not have as much of a direct impact on fish behaviour as previously thought, and we advocate for improved approaches to minimize the potential for a decline effect in future avenues of research.

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Understanding the metabolic capacity of Antarctic fishes to acclimate to future ocean conditions

Antarctic fishes have evolved under stable, extreme cold temperatures for millions of years. Adapted to thrive in the cold environment, their specialized phenotypes will likely render them particularly susceptible to future ocean warming and acidification as a result of climate change. Moving from a period of stability to one of environmental change, species persistence will depend on maintaining energetic equilibrium, or sustaining the increased energy demand without compromising important biological functions such as growth and reproduction. Metabolic capacity to acclimate, marked by a return to metabolic equilibrium through physiological compensation of resting metabolic rate (RMR), will likely determine which species will be better poised to cope with shifts in environmental conditions. Focusing on the suborder Notothenioidei, a dominant group of Antarctic fishes, and in particular 4 well-studied species, Trematomus bernacchii, Pagothenia borchgrevinki, Notothenia rossii and N. coriiceps, we discuss metabolic acclimation potential to warming and CO2-acidification using an integrative and comparative framework. There are species-specific differences in the physiological compensation of RMR during warming and the duration of acclimation time required to achieve compensation; for some species RMR fully recovered within 3.5 weeks of exposure, such as P. borchgrevinki, while for other species, such as N. coriiceps, RMR remained significantly elevated past 9 weeks of exposure. In all instances, added exposure to increased PCO2, further compromised the ability of species to return RMR to pre-exposure levels. The period of metabolic imbalance, marked by elevated RMR, was underlined by energetic disturbance and elevated energetic costs, which shifted energy away from fitness-related functions, such as growth. In T. bernacchii and N. coriiceps, long duration of elevated RMR impacted condition factor and/or growth rate. Low growth rate can affect development and ultimately the timing of reproduction, severely compromising the species’ survival potential and the biodiversity of the notothenioid lineage. Therefore, the ability to achieve full compensation of RMR, and in a short-time frame, in order to avoid long term consequences of metabolic imbalance, will likely be an important determinant in a species’ capacity to persist in a changing environment. Much work is still required to develop our understanding of the bioenergetics of Antarctic fishes in the face of environmental change, and a targeted approach of nesting a mechanistic focus in an ecological and comparative framework will better aid our predictions on the effect of global climate change on species persistence in the polar regions.

Continue reading ‘Understanding the metabolic capacity of Antarctic fishes to acclimate to future ocean conditions’

Intestinal response to ocean acidification in the European sea bass (Dicentrarchus labrax)


• High CO2 reduced specific growth rate in sea bass juveniles.

• High CO2 increased intestinal bicarbonate secretion in the anterior and mid intestine.

• High CO2 increased intestinal carbonate precipitates 4.4-fold.

• High CO2 increased intestinal expression for atp6v1b (V-ATPase β subunit), slc4a4, slc26a3, and slc26a6.


The intestine of marine fishes contributes to the ocean carbon cycle producing carbonate aggregates as part of the osmoregulatory process. Therefore, this study aimed to evaluate physiological adjustments of European sea bass (Dicentrarchus labrax) intestine to a higher pCO2 environment likely in the near future (~1700 μatm). At the whole-body level, hypercapnia for 5 weeks resulted in fish having a significantly diminished specific growth rate, condition factor and hepatosomatic index. An increase in plasma osmolality and HCO3− concentration was detected, paralleled by decreased metabolites concentrations. In the intestine, high seawater pCO2 was without effect on ouabain-sensitive ATPase activities, while Bafilomycin A1-sensitive ATPase activity significantly decreased in the anterior intestine. Anterior and mid intestine were mounted in Ussing chambers in order to measure bioelectrical parameters and bicarbonate secretion by pH-Stat ex-vivo. Hypercapnia induced a 2.3 and 2.8-fold increase in bicarbonate secretion rates in the anterior and mid intestine, respectively. In the intestinal fluid, HCO3− concentration increased 2.2-fold, and carbonate precipitates showed a 4.4-fold increase in response to hypercapnia, paralleled by a >3-fold increase of drinking and a >2-fold increase of intestinal volume at any given time. At the molecular level, hypercapnia elicited higher intestinal mRNA expression levels for atp6v1b (V-ATPase B subunit), slc4a4, slc26a3, and slc26a6, both in the anterior and mid intestine. As a whole, our results show that the intestine of sea bass responds to high seawater pCO2, a response that comes at a cost at the whole-body level with an impact in the fish specific growth rate, condition factor, and hepatosomatic index.

Continue reading ‘Intestinal response to ocean acidification in the European sea bass (Dicentrarchus labrax)’

Elevated temperature and CO2 have positive effects on the growth and survival of larval Australasian snapper


• Larval Snapper were positively affected by projected end of century temperature and pCO2 from fertilization to 16 days post-hatching.

• Elevated temperature increased the size of larvae, however high pCO2 had no effect.

• High pCO2 significantly increased survival at 16 days post-hatch, but elevated temperature had no effect.

• Some species and populations of marine fish exhibit positive effects from projected environmental change.


Rising water temperature and increased uptake of CO2 by the ocean are predicted to have widespread impacts on marine species. However, the effects are likely to vary, depending on a species’ sensitivity and the geographical location of the population. Here, we investigated the potential effects of elevated temperature and pCO2 on larval growth and survival in a New Zealand population of the Australasian snapper, Chrysophyrs auratus. Eggs and larvae were reared in a fully cross-factored experiment (18 °C and 22 °C/pCO2 440 and 1040 μatm) to 16 days post hatch (dph). Morphologies at 1 dph and 16 dph were significantly affected by temperature, but not CO2. At 1dph, larvae at 22 °C were longer (7%) and had larger muscle depth at vent (14%), but had reduced yolk (65%) and oil globule size (16%). Reduced yolk reserves in recently hatched larvae suggests higher metabolic demands in warmer water. At 16 dph, larvae at elevated temperature were longer (12%) and muscle depth at vent was larger (64%). Conversely, survival was primarily affected by CO2 rather than temperature. Survivorship at 1 dph and 16 dph was 24% and 54% higher, respectively, under elevated CO2 compared with ambient conditions. Elevated temperature increased survival (24%) at 1 dph, but not at 16 dph. These results suggest that projected climate change scenarios may have an overall positive effect on early life history growth and survival in this population of C. auratus. This could benefit recruitment success, but needs to be weighed against negative effects of elevated CO2 on metabolic rates and swimming performance observed in other studies on the same population.

Continue reading ‘Elevated temperature and CO2 have positive effects on the growth and survival of larval Australasian snapper’

An uncertain future: effects of ocean acidification and elevated temperature on a New Zealand snapper (Chrysophrys a uratus) population


• Modelling suggests the effect of climate change on snapper populations is uncertain.

• Impacts range from a 29% reduction to a 44% increase in fishery yield.

• These impacts are most likely mediated via impacts on recruitment.


Anthropogenic CO2 emissions are warming and acidifying Earth’s oceans, which is likely to lead to a variety of effects on marine ecosystems. Fish populations will be vulnerable to this change, and there is now substantial evidence of the direct and indirect effects of climate change on fish. There is also a growing effort to conceptualise the effects of climate change on fish within population models. In the present study knowledge about the response of New Zealand snapper to warming and acidification was incorporated within a stock assessment model. Specifically, a previous tank experiment on larval snapper suggested both positive and negative effects, and otolith increment analysis on wild snapper indicated that growth may initially increase, followed by a potential decline as temperatures continue to warm. As a result of this uncertainty, sensitivity analysis was performed by varying average virgin recruitment (R0) by ±30%, adult growth by ±6%, but adjusting mean size at recruitment by +48% as we had better evidence for this increase. Overall adjustments to R0 had the biggest impact on the future yield (at a management target of 40% of an unfished population) of the Hauraki Gulf snapper fishery. The most negative scenario suggested a 29% decrease in fishery yield, while the most optimistic scenario suggested a 44% increase. While largely uncertain, these results provide some scope for predicting future impacts on the snapper fishery. Given that snapper is a species where the response to climate change has been specifically investigated, increasing uncertainty in a future where climate change and other stressors interact in complex and unpredictable ways is likely to be an important consideration for the management of nearly all fish populations.

Continue reading ‘An uncertain future: effects of ocean acidification and elevated temperature on a New Zealand snapper (Chrysophrys a uratus) population’

Investigating the effects of climate co-stressors on surf smelt energy demands

Surf smelt (Hypomesus pretiosus) are ecologically and economically important to the Pacific Northwest. They play a critical role in the food web and support numerous commercially important species and are an economically important baitfish. Surf smelt interact closely with the nearshore environment, utilizing approximately 10% of Puget Sound coastlines for spawning throughout the year. Surf smelt spawn at high tide and adhere fertilized eggs to beach sediment, causing their embryos to be exposed to air and seawater throughout embryonic development. Because of this unique life history, surf smelt may be susceptible to anthropogenic stressors including coastal development and climate change. However, very few studies have attempted to test the tolerance of surf smelt to climate change, including elevated temperature and ocean acidification. The purpose of this study was to examine the interactive effects of climate co-stressors ocean acidification and seawater warming on the energy demands of developing surf smelt. Surf smelt embryos and larvae were collected and placed into experimental basins under three temperature treatments (12°C, 15°C, and 18°C) and two total carbon treatments (ambient and elevated) for a period of 14 days for the embryos, and 4 days for the larvae. Increased temperature significantly decreased yolk size in developing surf smelt embryos and larvae. During this time, embryo yolk sacs in the high temperature treatment were on average 10.2% smaller than embryo yolk sacs in ambient temperature water. Larval yolk and oil globules mirrored this trend with larvae in the high temperature treatment having on average 32.5% smaller yolk sacs and 20.0% smaller oil globules compared to larvae in ambient temperature. While no effect of acidification as a singular stressor was observed, the interaction with temperature significantly increased surf smelt embryo heart rates by 5% above ambient conditions. These results indicate that near-future climate change scenarios are going to impact the energy demands of developing surf smelt, a result that may have a variety of potential impacts including altered hatch times, larval deformities, and increased mortality, all of which will increase interannual variability in adult recruitment. The results of this study highlight the need to increase focus on studying surf smelt in the context of ecological and climate change research.

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Are long-term growth responses to elevated pCO2 sex-specific in fish?

Whether marine fish will grow differently in future high pCO2 environments remains surprisingly uncertain. Long-term and whole-life cycle effects are particularly unknown, because such experiments are logistically challenging, space demanding, exclude long-lived species, and require controlled, restricted feeding regimes—otherwise increased consumption could mask potential growth effects. Here, we report on repeated, long-term, food-controlled experiments to rear large populations (>4,000 individuals total) of the experimental model and ecologically important forage fish Menidia menidia (Atlantic silverside) under contrasting temperature (17°, 24°, and 28°C) and pCO2 conditions (450 vs. ~2,200 μatm) from fertilization to ~ a third of this annual species’ life span. Quantile analyses of trait distributions showed mostly negative effects of high pCO2 on long-term growth. At 17°C and 28°C, but not at 24°C, high pCO2 fish were significantly shorter [17°C: -5 to -9%; 28°C: -3%] and weighed less [17°C: -6 to -18%; 28°C: -8%] compared to ambient pCO2 fish. Reductions in fish weight were smaller than in length, which is why high pCO2 fish at 17°C consistently exhibited a higher Fulton’s k (weight/length ratio). Notably, it took more than 100 days of rearing for statistically significant length differences to emerge between treatment populations, showing that cumulative, long-term CO2 effects could exist elsewhere but are easily missed by short experiments. Long-term rearing had another benefit: it allowed sexing the surviving fish, thereby enabling rare sex-specific analyses of trait distributions under contrasting CO2 environments. We found that female silversides grew faster than males, but there was no interaction between CO2 and sex, indicating that males and females were similarly affected by high pCO2. Because Atlantic silversides are known to exhibit temperature-dependent sex determination, we also analyzed sex ratios, revealing no evidence for CO2-dependent sex determination in this species.

Continue reading ‘Are long-term growth responses to elevated pCO2 sex-specific in fish?’

The effects of constant and fluctuating elevated pCO2 levels on oxygen uptake rates of coral reef fishes


• Coral reefs exhibit natural, diel pCO2 fluctuations that are expected to increase.

• Few studies have examined effects of fluctuating pCO2 on adult coral reef fishes.

• We measured swimming, O2 uptake rates, aerobic scope, and various blood parameters.

• Performing under fluctuating pCO2 conditions may be less energetically-costly.

• Studies should use ecologically-relevant CO2 when predicting climate change impacts.


Ocean acidification, resulting from increasing atmospheric carbon dioxide (CO2) emissions, can affect the physiological performance of some fishes. Most studies investigating ocean acidification have used stable pCO2 treatments based on open ocean predictions. However, nearshore systems can experience substantial spatial and temporal variations in pCO2. Notably, coral reefs are known to experience diel fluctuations in pCO2, which are expected to increase on average and in magnitude in the future. Though we know these variations exist, relatively few studies have included fluctuating treatments when examining the effects of ocean acidification conditions on coral reef species. To address this, we exposed two species of damselfishes, Amblyglyphidodon curacao and Acanthochromis polyacanthus, to ambient pCO2, a stable elevated pCO2 treatment, and two fluctuating pCO2 treatments (increasing and decreasing) over an 8 h period. Oxygen uptake rates were measured both while fish were swimming and resting at low-speed. These 8 h periods were followed by an exhaustive swimming test (Ucrit) and blood draw examining swimming metrics and haematological parameters contributing to oxygen transport. When A. polyacanthus were exposed to stable pCO2 conditions (ambient or elevated), they required more energy during the 8 h trial regardless of swimming type than fish exposed to either of the fluctuating pCO2 treatments (increasing or decreasing). These results were reflected in the oxygen uptake rates during the Ucrit tests, where fish exposed to fluctuating pCO2 treatments had a higher factorial aerobic scope than fish exposed to stable pCO2 treatments. By contrast, A. curacao showed no effect of pCO2 treatment on swimming or oxygen uptake metrics. Our results show that responses to stable versus fluctuating pCO2 differ between species – what is stressful for one species many not be stressful for another. Such asymmetries may have population- and community-level impacts under higher more variable pCO2 conditions in the future.

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Transcriptional analysis reveals physiological response to acute acidification stress of barramundi Lates calcarifer (Bloch) in coastal areas

To understand the physiological response of estuarine fish to acidification, barramundi (Lates calcarifer) juveniles were exposed to acidified seawater in experimental conditions. The molecular response of barramundi to acidification stress was assessed by RNA-seq analysis. A total of 2188 genes were identified as differential expression genes. The gene ontology classification system and Kyoto Encyclopedia of Genes and Genomes database analysis showed that acidification caused differential expressions of genes and pathways in the gills of barramundi. Acidification had a great influence on the signal transduction pathway in cell process. Furthermore, we detected that numerous unigenes involved in the pathways associated with lipid metabolism, carbohydrate metabolism, amino acid metabolism, glycan biosynthesis and metabolism specific and non-specific immunity were changed. This study indicates that the physiological responses in barramundi especially the immune system and energy allocation correspond to the variation of environmental pH. This study reveals the necessity for assessment of the potential of estuarine fishes to cope with acidification of the environment and the need to develop strategies for fish conservation in coastal areas.

Continue reading ‘Transcriptional analysis reveals physiological response to acute acidification stress of barramundi Lates calcarifer (Bloch) in coastal areas’

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Ocean acidification in the IPCC AR5 WG II

OUP book