Posts Tagged 'fish'

Ocean acidification impacts fish larvae but warming could compensate juveniles

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A related article has been published: Effects of ocean acidification over successive generations decrease resilience of larval European sea bass to ocean acidification and warming but juveniles could benefit from higher temperatures in the NE Atlantic

A 40 day old European sea bass (Dicentrarchus labrax) larva: Photo credit: Sarah Howald.

As we pump more CO2 into the atmosphere, the pH of the oceans is decreasing and although a reduction of 0.1 pH units may not sound much, the reality is that the acidity of the seas has increased by 30% since the start of the Industrial Revolution in the 18th century. But no one knew how much of an impact decreasing pH might have on long-lived fish species. ‘Fish had been thought to be less vulnerable to ocean acidification due to well-developed acid–base regulation systems’, says Sarah Howald from the Alfred Wegener Institute for Polar and Marine Research (AWI), Germany. However, scientists have recently discovered that fish larvae may be more vulnerable than thought. Some grew faster in more acidic waters, while others suffered tissue and hearing damage in addition to growing more slowly. Yet, no one knew how ocean acidification might impact subsequent generations. Felix Mark from AWI, with colleagues from Germany and France, embarked on an ambitious 5.5 year investigation to find out how European sea bass (Dicentrarchus labrax) larvae and their eventual offspring deal with acidic conditions.

In October 2013, at the Ifremer-Centre de Bretagne, France, Guy Claireaux (University of Brest, France), José Zambonino and David Mazurais (both from Ifremer), Myron Peck (University of Hamburg, Germany) and Mark allocated recently hatched sea bass larvae to small tanks of seawater pumped in from the Bay of Brest at summer temperatures (19°C) while other larvae lived in tanks of seawater where the acidity had been raised to 1700 μatm CO2, the IPCC’s prediction for seawater CO2 concentrations 120 years in the future. Once the larvae had developed into juveniles (∼2.5 months old), the team relocated the youngsters to larger cool (15°C) tanks, maintaining the two different pH levels until the fish were adult (spring 2017), when the researchers selected ∼30 adult fish each from the two water conditions to rehome in palatial 3000 l tanks. Then, in March 2018, the 5 year old adults spawned to produce the next generation of larvae. But this time the scientists added a twist, dividing the offspring of the parents from the modern day (current CO2) seawater conditions and those of the parents raised in the acidic future water conditions (1700 μatm CO2) into cool and warm tanks, to simulate climate change. Meanwhile, the team kept track of the first and the second generations as they grew and developed.

Initially, the first generation of sea bass youngsters didn’t seem to be affected by their acidic start in life and neither did their offspring. However, when the team altered the water temperature as the second generation developed in the acidic future water, they found the larvae from the warmer (20°C) tank were much smaller when they metamorphosed into juveniles than those in cool acidic seawater and those that developed in modern warm water. Mark suspects that the warmer high-CO2 conditions in the future could impair energy production by the youngsters’ mitochondria, limiting their growth. However, once the larvae developed into juvenile fish, they seemed to benefit, growing faster, although the team isn’t sure whether the warmth was accelerating the fish’s growth or whether the acidity failed to impair the growing juveniles.

The team warns that the faster growth of larvae in a warmer more acidic world could place them at risk if there is insufficient food for the rapidly growing youngsters. But it seems that if the youngsters develop successfully into juvenile fish, their chances may improve.

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Otolith development and elemental incorporation in response to seawater acidification in the flounder Paralichthys olivaceus at early life stages


  • Ocean acidification promoted otolith growth but not changed otolith shape.
  • Ocean acidification did not alter somatic growth or otolith elemental incorporation.
  • Ocean acidification induced and increased the occurrence of irregular calcitic otoliths.
  • Elemental incorporation is higher in aragonitic otoliths than in calcitic otoliths.


Ocean acidification can influence the formation, development and functions of calcified structures in marine organisms, such as otoliths, which are mainly composed of calcium carbonate (CaCO3) and function in orientation, balance, sensory perception and locomotion in fish. This study investigated the impacts of seawater acidification (pH 8.10, 7.70 and 7.30, roughly corresponding to the ocean acidification under RCP 8.5 scenario predicted by the IPCC) on somatic growth, otolith (aragonite) morphology and microchemistry in the flounder Paralichthys olivaceus at early life stages (ELSs, exposed to acidified seawater via pCO2 from embryonic to juvenile stages for 52 days). The results demonstrated that seawater acidification promoted otolith growth (mass and size) but did not change their geometric outlines. Seawater acidification did not alter the somatic growth or otolith elemental incorporation (Sr, Ba and Mg) in the flounder. Seawater acidification increased the occurrence of abnormally developed calcitic otoliths (calcite) which considerably differed from the aragonitic otoliths in surface and crystal structures. Additionally, elemental incorporation (Sr:Ca and Ba:Ca) appeared to be higher in aragonitic otoliths than in calcitic otoliths, which was likely related to their unique manners of formation. Our results agreed with the broad literature, in that seawater acidification showed species-specific influences (positive or no effect) on otolith size but did not affect somatic growth, otolith shape or elemental incorporation of fish at ELSs. These findings provide knowledge for evaluating the ecological effects of ocean acidification on the recruitment and population dynamics of fish in the wild.

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Metabolic effect of ocean acidification on common cuttlefish Sepia officinalis early stages

Atmospheric carbon dioxide (CO2) emissions are continuously increasing due to the growing anthropogenic activities, causing a rise in the sea-surface partial pressure of CO2 (pCO2). This change in turn leads to decreased ocean pH, named ocean acidification, and affects the carbonate-silicate cycle. Such modification of seawater chemistry also affects the physiology and behaviour of marine organisms, impacting their metabolism, growth and development during vulnerable early-life stages. Among them, the embryo of the cephalopod cuttlefish develops for ~2 months) in encapsulated eggs with harsh conditions of hypoxia and hypercapnia, potentially worsen by the environmental ocean acidification. In this study, the development and the growth of early-life stages of Sepia officinalis were followed during the whole embryonic developmental period up to 10 days post-hatchling juveniles. Embryos and juveniles were exposed to five elevated pCO2 conditions controlled with a continuous pH-stat system (pH 8.08; 7.82; 7.65; 7.54; 7.43). Metabolites were determined in ready-to-hatch embryos, just hatched embryos and 10 d-old juveniles, using a 1H nuclear magnetic resonance (NMR) spectroscopy as a platform for untargeted metabolomics analysis. Consistent with previous studies, our results showed longer embryonic development and decreased hatching success at the lowest pH, but no effect on juvenile weight upon hatching. Metabolomics analysis revealed a metabolic depression in embryos reared at pH 7.43, non-monotonic changes to pH in 10 d-old juveniles, and no clear pH effect in newly hatched juvenile cuttlefish, likely due to the metabolic stress associated with hatching. Those results reveal possible effect of ocean acidification on the cuttlefish recruitment.

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Ocean futures for the world’s largest yellowfin tuna population under the combined effects of ocean warming and acidification

The impacts of climate change are expected to have profound effects on the fisheries of the Pacific Ocean, including its tuna fisheries, the largest globally. This study examined the combined effects of climate change on the yellowfin tuna population using the ecosystem model SEAPODYM. Yellowfin tuna fisheries in the Pacific contribute significantly to the economies and food security of Pacific Island Countries and Territories and Oceania. We use an ensemble of earth climate models to project yellowfin populations under a high greenhouse gas emissions (IPCC RCP8.5) scenario, which includes, the combined effects of a warming ocean, increasing acidification and changing ocean chemistry. Our results suggest that the acidification impact will be smaller in comparison to the ocean warming impact, even in the most extreme ensemble member scenario explored, but will have additional influences on yellowfin tuna population dynamics. An eastward shift in the distribution of yellowfin tuna was observed in the projections in the model ensemble in the absence of explicitly accounting for changes in acidification. The extent of this shift did not substantially differ when the three-acidification induced larval mortality scenarios were included in the ensemble; however, acidification was projected to weaken the magnitude of the increase in abundance in the eastern Pacific. Together with intensive fishing, these potential changes are likely to challenge the global fishing industry as well as the economies and food systems of many small Pacific Island Countries and Territories. The modelling framework applied in this study provides a tool for evaluating such effects and informing policy development.

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Effects of ocean acidification on Lythrypnus dalli reproductive output and behavior

Reproduction in fishes is an energetically costly but vital process that is important to nearshore fisheries and proper ecosystem functioning. Successful fish reproduction is generally limited to a narrow breadth of specific environmental conditions, and variation in these conditions may affect the ability of fish to allocate energy towards reproduction. In particular, ocean acidification (OA) is generally assumed to be a major threat to fish reproduction, but past studies on the effects of OA have produced variable results. To examine how OA affects bluebanded goby (Lythrypnus dalli) reproduction, female reproductive output and male reproductive behaviors were quantified under two experimental treatments that represent differences between present-day (ambient) and future OA (decreased by 0.2 pH units) conditions. To do this, sexually mature bluebanded gobies were placed in laboratory mesocosms for continuous seven-day trials and allowed to reproduce in artificial nests. Four artificial nests were placed in each of the four mesocosms to provide fish with similar nesting habitats to encourage reproduction. Each mesocosm included similar fish size structures and numbers of female gobies to control for any size- or sex-dependent responses. Male reproductive behavior was quantified daily through visual assessment of their movement patterns within each mesocosm. Female reproductive output was quantified by checking the nests for the presence of eggs, which were photographed to evaluate egg quantity, size, and development. Results indicate that future OA conditions did not significantly affect any of the reproducti on metrics examined in this study. These results suggest that future changes in environmental factors such as seawater pH may not have dramatic effects on the reproductive output and behavior of bluebanded gobies.

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Raw data concerning the carbonate system and the sensory behaviour of juvenile Dicentrarchus labrax in response to mechano-acoustic and visual cues under ocean warming and acidification

This data set is linked to a study that sought to investigate whether a mid-term 92-days exposure to warming and/or acidification alters the visual or mechano-acoustic sensory channels of the European sea bass Dicentrarchus labrax when it comes to detect and avoid simulated avian predator cues. Juveniles, aged between 283 to 316 days post hatching, were challenged in separate behavioural trials to assess their reaction facing either a shadow (visual cue) or a falling object (mechano-acoustic cue). These cues were intended to mimic an overflying bird or a bird swoop attack, respectively.

To follow the best practices of ocean acidification, the 1st and 2nd tabs show daily measurements of temperature and pH (in NIST scale). The 3rd tab shows weekly measurements of temperature and pH (in NIST and total scale), salinity, oxygen and total alkalinity that were used to calculate the carbonate system parameters, which is also shown in the 3rd tab.

Total body length (in cm, from the nose tip to end of caudal fin) was measured in a sample of 74 alive individuals upon arrival (4th tab) or in 379 dead individuals once the behavioural tests were ended (5th tab).

Abbreviations for the kinematic behavioural variables evaluated during the behavioural tests are available in the 6th tab. Data set for both the visual behavioural tests (7th tab) and the mechano-acoustic behavioural tests (8th tab) were used to run the linear mixed-effects models.

Continue reading ‘Raw data concerning the carbonate system and the sensory behaviour of juvenile Dicentrarchus labrax in response to mechano-acoustic and visual cues under ocean warming and acidification’

Partial raw data of the carbonate system after years of transgenerational exposure to ocean acidification in the European sea bass Dicentrarchus labrax

This data set is linked to a study that sought to investigate the impacts of long-term ocean acidification on the olfactory rosette transcriptome of the European sea bass (Dicentrarchus labrax) and on viral resistance.  We exposed two generations of the D. labrax to end-of-century predicted pH levels (IPCC RCP8.5), with parents being exposed for 53 months (F1) and their offspring for 18 months (F2). 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.
This data set contains physico-chemical parameters of the rearing sea water including the carbonate system components as well as survival data and temperature measurements during the viral challenge.
The rearing periods extends as follows:
F1 parents: 24 October 2013 – 26 March 2018; in duplica tanks per treatment
F2 eggs phase: 27 March 2018 – 31 March 2018; in a simplica per treatment
F2 larval phase: 1 April 2018 – 1 June 2018; in triplica tanks per treatment
F2 juvenile phase: 2 April 2018 – 17 October 2019; in a duplica per treatment
However, since this study extends over 7 years, some data is not available in digital form but in paper form. Therefore, here we provide digitalized data for the following periods.
F1 parents: 8 February 2016 – 6 March 2018; monthly data showing physico-chemical and carbonate parameters of the sea water
F2 eggs phase: 27 March 2018 – 31 March 2018; daily data showing the pH and temperature of the sea water
F2 larval phase: 1 April 2018 – 1 June 2018; monthly data showing physico-chemical and carbonate parameters of the sea water and daily data showing the pH and temperature of the sea water
F2 juvenile phase:   2 April 2018 – 24 October 2018; daily data showing the pH and temperature of the sea water
F2 juvenile phase:   2 April 2018 – 11 February 2019; monthly data showing physico-chemical and carbonate parameters of the sea water
pH in NIST scale and temperature were daily measured with a WTW 3110 pH meter (Xylem Analytics Germany, Weilheim, Germany; with electrode: WTW Sentix 41) calibrated daily with pH4.0 and pH7.0 buffers (WTW, Germany). Total alkalinity was measured following the adapted protocol of Strickland and Parsons: a 50 ml sample of filtered tank seawater was mixed with 15 ml HCl (0.01 M) and pH was measured immediately. The software CO2SYS using the constants from Mehrbach et al. refitted by Dickson and Millero were used to calculate pH in NIST scale to total scale and the carbonate chemistry components.
Continue reading ‘Partial raw data of the carbonate system after years of transgenerational exposure to ocean acidification in the European sea bass Dicentrarchus labrax’

CO2 induced seawater acidification impacts survival and development of European eel embryos

Fish embryos may be vulnerable to seawater acidification resulting from anthropogenic carbon dioxide (CO2) emissions or from excessive biological CO2 production in aquaculture systems. This study investigated CO2 effects on embryos of the European eel (Anguilla anguilla), a catadromous fish that is considered at risk from climate change and that is targeted for hatchery production to sustain aquaculture of the species. Eel embryos were reared in three independent recirculation systems with different pH/CO2 levels representing “control” (pH 8.1, 300 μatm CO2), end-of-century climate change (“intermediate”, pH 7.6, 900 μatm CO2) and “extreme” aquaculture conditions (pH 7.1, 3000 μatm CO2). Sensitivity analyses were conducted at 4, 24, and 48 hours post-fertilization (hpf) by focusing on development, survival, and expression of genes related to acute stress response (crhr1crfr2), stress/repair response (hsp70hsp90), water and solute transport (aqp1aqp3), acid-base regulation (nkcc1ancccar15), and inhibitory neurotransmission (GABAAα6bGabra1). Results revealed that embryos developing at intermediate pH showed similar survival rates to the control, but egg swelling was impaired, resulting in a reduction in egg size with decreasing pH. Embryos exposed to extreme pH had 0.6-fold decrease in survival at 24 hpf and a 0.3-fold change at 48 compared to the control. These observed effects of acidification were not reflected by changes in expression of any of the here studied genes. On the contrary, differential expression was observed along embryonic development independent of treatment, indicating that the underlying regulating systems are under development and that embryos are limited in their ability to regulate molecular responses to acidification. In conclusion, exposure to predicted end-of-century ocean pCO2 conditions may affect normal development of this species in nature during sensitive early life history stages with limited physiological response capacities, while extreme acidification will negatively influence embryonic survival and development under hatchery conditions.

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Effects of ocean acidification over successive generations decrease larval resilience to ocean acidification & warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic

European sea bass (Dicentrarchus labrax) is a large, economically important fish species with a long generation time whose long-term resilience to ocean acidification (OA) and warming (OW) is not clear. We incubated sea bass from Brittany (France) for two generations (>5 years in total) under ambient and predicted OA conditions (PCO2: 650 and 1700 µatm) crossed with ambient and predicted ocean OW conditions in F1 (temperature: 15-18°C and 20-23°C) to investigate the effects of climate change on larval and juvenile growth and metabolic rate.

We found that in F1, OA as single stressor at ambient temperature did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine and juvenile standard metabolic rates were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA as a single stressor on metabolic rates. Juvenile PO2crit was not affected by OA or OAW in both generations.

We discuss the potential underlying mechanisms resulting in the resilience of F0 and F1 larvae and juveniles to OA and in the beneficial effects of OW on F1 larval growth and metabolic rate, but on the other hand in the vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

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The olfactory tract: basis for future evolution in response to rapidly changing ecological niches

Within the forebrain the olfactory sensory system is unique from other sensory systems both in the projections of the olfactory tract and the ongoing neurogenic potential, characteristics conserved across vertebrates. Olfaction plays a crucial role in behaviors such as mate choice, food selection, homing, escape from predators, among others. The olfactory forebrain is intimately associated with the limbic system, the region of the brain involved in learning, memory, and emotions through interactions with the endocrine system and the autonomic nervous system. Previously thought to lack a limbic system, we now know that teleost fishes process emotions, have exceptional memories, and readily learn, behaviors that are often associated with olfactory cues. The association of neuromodulatory hormones, and more recently, the immune system, with odor cues underlies behaviors essential for maintenance and adaptation within natural ecological niches. Increasingly anthropogenic perturbations affecting ecosystems are impacting teleost fishes worldwide. Here we examine the role of the olfactory tract as the neural basis for the integration of environmental cues and resulting behaviors necessary for the regulation of biotic interactions that allow for future adaptation as the climate spins out of control.

“I should think we might fairly gauge the future of biological science, centuries ahead, by estimating the time it will take to reach a complete, comprehensive understanding of odor. It may not seem a profound enough problem to dominate all the life sciences, but it contains, piece by piece all the mysteries.”

—Lewis Thomas (1985).

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Characterization factors for ocean acidification impacts on marine biodiversity

Rising greenhouse gas emissions do not only accelerate climate change but also make the ocean more acidic. This applies above all to carbon dioxide (CO2). Lower ocean pH levels threaten marine ecosystems and especially strongly calcifying species. Impacts on marine ecosystem quality are currently underrepresented in life cycle assessments (LCAs). Here, we developed characterization factors for the life cycle impact assessment of ocean acidification. Our main contribution was developing new species sensitivity distributions (SSDs), from which we derived effect factors for different impact perspectives: Marginal, linear, and average changes for both the past and four future emission scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). Based on a dataset that covered five taxa (corals, crustaceans, echinoderms, fishes, molluscs) and three climate zones, we showed significantly higher sensitivities for strongly calcifying than slightly calcifying taxa and in polar regions compared to tropical and temperate regions. Experimental duration, leading to acute, subchronic, or chronic toxicological endpoints, did not significantly affect the species sensitivities. With ocean acidification impacts still accelerating, the future-oriented average effects are higher than the marginal or past-oriented average effects. While our characterization factors are ready for use in LCA, we also point to opportunities for improvement in future developments.

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Reanalysis shows the extreme decline effect does not exist in fish ocean acidification studies

Contradictory Results

A meta-analysis published in PLoS Biology by Clements et al. (2022) claims there is an extreme decline effect in studies published between 2009-2019 on the impacts of ocean acidification (OA) on fish behaviour. Here I show that the extreme decline effect reported by Clements et al. is a statistical artifact caused by the way they corrected for zero values in percentage data, which was more common in the earliest experiments compared with later studies. Furthermore, selective choices for excluding or including data, along with serious errors in the compilation of data and missing studies with strong effects, weakened the effect sizes reported for papers after 2010, further exacerbating the decline effect reported by Clements et al. When the data is reanalyzed using appropriate corrections for zero values in percentage and proportional data, and using a complete, corrected and properly screened data set, the extreme decline effect reported by Clements et al. no longer exists.

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Global climate change and the Baltic Sea ecosystem: direct and indirect effects on species, communities and ecosystem functioning

Climate change has multiple effects on Baltic Sea species, communities and ecosystem functioning through changes in physical and biogeochemical environmental characteristics of the sea. Associated indirect and secondary effects on species interactions, trophic dynamics and ecosystem function are expected to be significant. We review studies investigating species-, population- and ecosystem-level effects of abiotic factors that may change due to global climate change, such as temperature, salinity, oxygen, pH, nutrient levels, and the more indirect biogeochemical and food web processes, primarily based on peer-reviewed literature published since 2010.

For phytoplankton, clear symptoms of climate change, such as prolongation of the growing season, are evident and can be explained by the warming, but otherwise climate effects vary from species to species and area to area. Several modelling studies project a decrease of phytoplankton bloom in spring and an increase in cyanobacteria blooms in summer. The associated increase in N:P ratio may contribute to maintaining the “vicious circle of eutrophication”. However, uncertainties remain because some field studies claim that cyanobacteria have not increased and some experimental studies show that responses of cyanobacteria to temperature, salinity and pH vary from species to species. An increase of riverine dissolved organic matter (DOM) may also decrease primary production, but the relative importance of this process in different sea areas is not well known. Bacteria growth is favoured by increasing temperature and DOM, but complex effects in the microbial food web are probable. Warming of seawater in spring also speeds up zooplankton growth and shortens the time lag between phytoplankton and zooplankton peaks, which may lead to decreasing of phytoplankton in spring. In summer, a shift towards smaller-sized zooplankton and a decline of marine copepod species has been projected.

In deep benthic communities, continued eutrophication promotes high sedimentation and maintains good food conditions for zoobenthos. If nutrient abatement proceeds, improving oxygen conditions will first increase zoobenthos biomass, but the subsequent decrease of sedimenting matter will disrupt the pelagic–benthic coupling and lead to a decreased zoobenthos biomass. In the shallower photic systems, heatwaves may produce eutrophication-like effects, e.g. overgrowth of bladderwrack by epiphytes, due to a trophic cascade. If salinity also declines, marine species such as bladderwrack, eelgrass and blue mussel may decline. Freshwater vascular plants will be favoured but they cannot replace macroalgae on rocky substrates. Consequently invertebrates and fish benefiting from macroalgal belts may also suffer. Climate-induced changes in the environment also favour establishment of non-indigenous species, potentially affecting food web dynamics in the Baltic Sea.

As for fish, salinity decline and continuing of hypoxia is projected to keep cod stocks low, whereas the increasing temperature has been projected to favour sprat and certain coastal fish. Regime shifts and cascading effects have been observed in both pelagic and benthic systems as a result of several climatic and environmental effects acting synergistically.

Knowledge gaps include uncertainties in projecting the future salinity level, as well as stratification and potential rate of internal loading, under different climate forcings. This weakens our ability to project how pelagic productivity, fish populations and macroalgal communities may change in the future. The 3D ecosystem models, food web models and 2D species distribution models would benefit from integration, but progress is slowed down by scale problems and inability of models to consider the complex interactions between species. Experimental work should be better integrated into empirical and modelling studies of food web dynamics to get a more comprehensive view of the responses of the pelagic and benthic systems to climate change, from bacteria to fish. In addition, to better understand the effects of climate change on the biodiversity of the Baltic Sea, more emphasis should be placed on studies of shallow photic environments.

The fate of the Baltic Sea ecosystem will depend on various intertwined environmental factors and on development of the society. Climate change will probably delay the effects of nutrient abatement and tend to keep the ecosystem in its “novel” state. However, several modelling studies conclude that nutrient reductions will be a stronger driver for ecosystem functioning of the Baltic Sea than climate change. Such studies highlight the importance of studying the Baltic Sea as an interlinked socio-ecological system.

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Impaired hatching exacerbates the high CO2 sensitivity of embryonic sand lance Ammodytes dubius

Rising oceanic pCO2 levels could affect many traits in fish early life stages, but only few species to date have shown direct CO2-induced survival reductions. This might partly be because species from less CO2-variable, offshore environments in higher latitudes are currently underrepresented in the literature. We conducted new experimental work on northern sand lance Ammodytes dubius, a keystone forage fish on offshore Northwest Atlantic sand banks, which was recently suggested to be highly CO2-sensitive. In two complementary trials, we produced embryos from wild, Gulf of Maine (GoM) spawners and reared them at several pCO2 levels (~400–2000 µatm) in combination with static (6, 7, 10°C) and dynamic (10 → 5°C) temperature treatments. Again, we consistently observed large, CO2-induced reductions in hatching success (–23% at 1000 µatm, -61% at ~2000 µatm), and the effects were temperature-independent. To distinguish pCO2 effects during development from potential impacts on hatching itself, some embryos were switched between high and control pCO2 treatments just prior to hatch. This indeed altered hatching patterns consistent with the CO2-impaired hatching hypothesis. High CO2 also delayed the day of first hatch in one trial and peak hatch in the other, where later-hatched larvae were of similar size but with progressively less endogenous energy reserves. For context, we extracted seasonal pCO2 projections for Stellwagen Bank (GoM) from regional ensemble simulations, which indicated a CO2-induced reduction in sand lance hatching success to 71% of contemporary levels by 2100. The species’ unusual CO2 sensitivity has large ecological and scientific ramifications that warrant future in-depth research.

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Phenotypic responses in fish behaviour narrow as climate ramps up

Natural selection alters the distribution of phenotypes as animals adjust their behaviour and physiology to environmental change. We have little understanding of the magnitude and direction of environmental filtering of phenotypes, and therefore how species might adapt to future climate, as trait selection under future conditions is challenging to study. Here, we test whether climate stressors drive shifts in the frequency distribution of behavioural and physiological phenotypic traits (17 fish species) at natural analogues of climate change (CO2 vents and warming hotspots) and controlled laboratory analogues (mesocosms and aquaria). We discovered that fish from natural populations (4 out of 6 species) narrowed their phenotypic distribution towards behaviourally bolder individuals as oceans acidify, representing loss of shyer phenotypes. In contrast, ocean warming drove both a loss (2/11 species) and gain (2/11 species) of bolder phenotypes in natural and laboratory conditions. The phenotypic variance within populations was reduced at CO2 vents and warming hotspots compared to control conditions, but this pattern was absent from laboratory systems. Fishes that experienced bolder behaviour generally showed increased densities in the wild. Yet, phenotypic alterations did not affect body condition, as all 17 species generally maintained their physiological homeostasis (measured across 5 different traits). Boldness is a highly heritable trait that is related to both loss (increased mortality risk) and gain (increased growth, reproduction) of fitness. Hence, climate conditions that mediate the relative occurrence of shy and bold phenotypes may reshape the strength of species interactions and consequently alter fish population and community dynamics in a future ocean.

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Resilience of black sea bass embryos to increased levels of carbon dioxide

After a decade of research on how embryonic fish will respond to the increased dissolved carbon dioxide (ρCO2) levels predicted for the next century, no uniform response to near future acidification has been observed among marine species. We exposed Black Sea Bass Centropristis striata (BSB) embryos to varied levels of ρCO2 (microatmospheres [μatm]) for 48 h during seasonal experiments conducted in 2013–2015 to compare embryonic response among multiple broodstocks. The relationship between ρCO2 concentration and hatching success was inconsistent among years, with a nonlinear, inverse relationship noted in 2014 only, explaining 13% of observed variance. Conversely, ρCO2 was a good predictor of unhatched BSB embryos after 48 h for all years combined (39%) and for 2013 (38%). The ρCO2 concentration was a good predictor of the frequency of vertebral column anomalies for individual years (2013: 40%; 2014: 12%; 2015: 38%) but not when data were pooled for all years. In 2013 and 2015, vertebral column anomalies were relatively consistent below 1,000 μatm and were elevated above that threshold. Preliminary results suggest that BSB embryos may demonstrate resilience to future ρCO2 levels, but the results also highlight the challenges associated with drawing broad conclusions given observed variability in results obtained from different broodstocks and study years.

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pH regulates the formation and hatching of Cryptocaryon irritans tomonts, which affects cryptocaryoniasis occurrence in Larimichthys crocea aquaculture


Cryptocaryon irritans are the main pathogens of white spot disease in marine teleost. However, the occurrence of cryptocaryoniasis is influenced by several abiotic factors including the pH. To explore the effect of pH on the life cycle of C. irritans (encystment, cleavage, and hatchability), protomonts and tomonts of C. irritans were incubated in seawater of 10 different pH levels (2–11). pH 8 was used as the control. The change in morphology and infectivity of theronts that hatched from tomonts against Larimichthys crocea were then recorded. We found that pH 6–9 had no significant effect on the encystment, cleavage, and hatching of the parasites. However, pH beyond this limit decreased the cleavage and hatching of the tomonts. Furthermore, extreme pH decreased the number of theronts hatched by each tomont and the pathogenicity of the theronts, but increased the aspect ratio of the theronts. Infectivity experiments further revealed that extreme pH significantly decreased the infectivity of C. irritans against L. crocea. In conclusion, the C. irritans can survive in pH of 5 to 10, but pH 6–9 is the optimal range for the reproduction and infectivity of C. irritans. However, extreme pH negatively affects these aspects.


Cryptocaryon irritans is a ciliate parasite that causes “white spot disease” in marine teleosts. The disease outbreak is influenced by hosts and a range of abiotic factors, such as temperature, salinity, and pH. Studies have shown that change in pH of seawater affects the structure (diversity and abundance of marine organisms) of marine ecosystem. However, how pH affects the life cycle and survival of C. irritans, and how future ocean acidification will affect the occurrence of cryptocaryoniasis, are not well understood. In this study, we explored the effect of pH on the formation and hatching of C. irritans tomonts. The findings of this study provide the foundation of the environmental adaptation of C. irritans, the occurrence of cryptocaryoniasis, and better management of marine fish culture.

Continue reading ‘pH regulates the formation and hatching of Cryptocaryon irritans tomonts, which affects cryptocaryoniasis occurrence in Larimichthys crocea aquaculture’

Swimming performance of sharks and rays under climate change

Climate change stressors (e.g., warming and ocean acidification) are an imminent challenge to the physiological performance of marine organisms. Several studies spanning the last decade have reported widespread effects of warming and acidification on marine fishes, especially teleosts, but more work is needed to elucidate the responses in marine elasmobranchs, i.e., sharks and rays. Dispersal capacity, as a result of locomotor performance, is a crucial trait that will determine which group of elasmobranchs will be more or less vulnerable to changes in the environment. In fact, efficient and high locomotor performance may determine the capacity for elasmobranchs to relocate to a more favorable area. In this review we integrate findings from work on locomotion of marine sharks and rays to identify characteristics that outline potential vulnerabilities and strength of sharks and rays under climate change. Traits such as intraspecific variability in response to climatic stressors, wide geographic range, thermotaxis, fast swimming or low energetic costs of locomotion are likely to enhance the capacity to disperse. Future studies may focus on understanding the interacting effect of climatic stressors on morphology, biomechanics and energetics of steady and unsteady swimming, across ontogeny and species.

Continue reading ‘Swimming performance of sharks and rays under climate change’

GABA receptors in the olfactory epithelium of the gilthead seabream (Sparus aurata)

Exposure to high PCO2/low pH seawater induces behavioural alterations in fish; a possible explanation for this is a reversal of Cl/HCO3 currents through GABAA receptors (the GABAA receptor theory). However, the main evidence for this is that gabazine, a GABAA receptor antagonist, reverses these effects when applied to the water, assuming that exposure to systems other than the CNS would be without effect. Here, we show the expression of both metabotropic and ionotropic GABA receptors, and the presence of GABAA receptor protein, in the olfactory epithelium of gilthead seabream. Furthermore, exposure of the olfactory epithelium to muscimol (a specific GABAA receptor agonist) increases or decreases the apparent olfactory sensitivity to some odorants. Thus, although the exact function of GABAA receptors in the olfactory epithelium is not yet clear, this may complicate the interpretation of studies wherein water-borne gabazine is used to reverse the effects of high CO2 levels on olfactory-driven behaviour in fish.

Continue reading ‘GABA receptors in the olfactory epithelium of the gilthead seabream (Sparus aurata)’

Ocean acidification affects the expression of neuroplasticity and neuromodulation markers in seabream

A possible explanation for acidification-induced changes in fish behaviour is that acidification interferes with neurogenesis and modifies the plasticity of neuronal circuitry in the brain. We tested the effects on the olfactory system and brain of gilthead seabream (Sparus aurata) of four weeks’ exposure to OA. Olfactory epithelium (OE) morphology changed shortly after OA exposure and persisted over the four-weeks. Expression of genes related to olfactory transduction, neuronal excitability, synaptic plasticity, GABAergic innervation, and cell proliferation were unchanged in the OE and olfactory bulb (OB) after four weeks’ exposure. Short-term changes in the ionic content of plasma and extradural fluid (EDF) returned to control levels after four weeks exposure, except for [Cl-] which remained elevated. This suggests that, in general, there is an early physiological response to OA and by four weeks a new homeostatic status is achieved. However, expression of genes involved in proliferation, differentiation and survival of undifferentiated neurons were modified in the brain. In the same brain areas, expression of thyroid hormone signalling genes was altered suggesting modifications in the thyroid-system may be linked to the changes in neuroplasticity and neurogenesis. Overall, the results of the current study are consistent with and effect of OA on neuroplasticity.

Continue reading ‘Ocean acidification affects the expression of neuroplasticity and neuromodulation markers in seabream’

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