Posts Tagged 'fish'

Reanalysis shows there is not an extreme decline effect in fish ocean acidification studies

Clements and colleagues [1] claim there is an extreme decline effect in studies published between 2009 and 2019 on the impacts of ocean acidification (OA) on fish behaviour, with the modelled average effect size declining from >5 in 2009 to 2010 to <0.5 after 2015. Here, I show that the extreme decline effect reported by Clements and colleagues 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 data compilation errors and missing studies with strong effects, weakened the effect sizes reported for papers after 2010, further exacerbating the decline effect reported by Clements and colleagues. When the data is reanalysed using appropriate corrections for zeros in percentage and proportional data and using a complete, corrected, and properly screened data set, the extreme decline effect reported by Clements and colleagues no longer exists (Fig 1A and 1B). Instead, there is a more gentle and consistent decline in effect size magnitude through time, from a modelled average <3 in 2009 to 2010 (Fig 1C) and remaining well above zero in 2018 to 2019 (Fig 1D).

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Transcriptomic analysis of large yellow croaker (Larimichthys crocea) during early development under hypoxia and acidification stress

Simple Summary

The large yellow croaker is one of the most economically important fish in China. In recent years, the deterioration of the water environment and unregulated aquaculture have caused great economic losses to the large yellow croaker breeding industry. The aim of this study was to analyze the effects of hypoxia and acidification stress on large yellow croaker. This study revealed that hypoxia and acidification stress suppressed the growth of the large yellow croaker. Transcriptome analysis revealed that genes of the collagen family play an important role in the response of large yellow croaker to hypoxia and acidification stress. The study elucidates the mechanism underlying the response of large yellow croaker to hypoxia–acidification stress during early development and provides a basic understanding of the potential combined effects of reduced pH and dissolved oxygen on Sciaenidae fishes.

Abstract

Fishes live in aquatic environments and several aquatic environmental factors have undergone recent alterations. The molecular mechanisms underlying fish responses to hypoxia and acidification stress have become a serious concern in recent years. This study revealed that hypoxia and acidification stress suppressed the growth of body length and height of the large yellow croaker (Larimichthys crocea). Subsequent transcriptome analyses of L. crocea juveniles under hypoxia, acidification, and hypoxia–acidification stress led to the identification of 5897 differentially expressed genes (DEGs) in the five groups. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that several DEGs were enriched in the ‘protein digestion and absorption’ pathway. Enrichment analysis revealed that this pathway was closely related to hypoxia and acidification stress in the five groups, and we found that genes of the collagen family may play a key role in this pathway. The zf-C2H2 transcription factor may play an important role in the hypoxia and acidification stress response, and novel genes were additionally identified. The results provide new clues for further research on the molecular mechanisms underlying hypoxia–acidification tolerance in L. crocea and provides a basic understanding of the potential combined effects of reduced pH and dissolved oxygen on Sciaenidae fishes.

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Effect of temperature and CO2 concentration on the morphogenesis of sagittal otoliths in Atlantic herring (Clupea harengus) larvae

Otoliths are very useful biomarkers especially for fish growth. Climate change with the associated global changes in warming and acidification could affect the calcification and the shape of otoliths during the crucial larval period in teleost fish. To evaluate this predicted combined effect of temperature and CO2, Atlantic herring (Clupea harengus) embryos and larvae were reared from hatching to respectively 47 and 60 days post-hatching (dph), under present day conditions and a scenario predicted for the year 2100 (IPCC RCP8.5). Otolith morphogenesis was tracked by analyzing area and normalized Elliptical Fourier coefficients. We found that otolith area for fish of similar size increased under the predicted 2100 climate change scenario compared to the present day. Climate change does not, however, seem to directly affect the otolith shape. Finally, the onset of otolith morphogenesis is hardwired, but the relationship between otolith and fish size is environment-dependent.

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Effects of ocean acidification and hypoxia on stress and growth hormone responses in juvenile blue rockfish (Sebastes mystinus)

Global climate change is causing increasing ocean acidification (OA) and deoxygenation (hypoxia) of coastal oceans. Along the coast of California, where upwelling is a dominant seasonal physical process, these environmental stressors often co-occur and are intensified in nearshore ecosystems. For juvenile nearshore fishes, who spend a crucial developmental life stage in coastal kelp forests during the upwelling season, these stressors are experienced concurrently and may have large implications for fitness. Environmental stress can set off an endocrine response, which impacts physiology, energy allocation, growth, and behavior. To test the effects of climate change on juvenile blue rockfish, I measured the endocrine response to single and combined stressors of OA and hypoxia after one week of exposure. Assays of cortisol and IGF-1 hormone responses, served as proxies for stress and growth, respectively. Full organismal effects of environmental stressors were evaluated using a scototaxis (i.e., light/dark anxiety) behavior test, and measures of physiological changes in maximum metabolic rate (MMR) and body condition (i.e., Fulton’s K condition index). I found that peak (~1 hour) cortisol levels were highest in the single stressor low pH (7.3 pH), followed by the combined stressor (7.3 pH and 2.0 mg/L O2) and then the single stressor hypoxic treatment (2.0 mg/l O2). This high peak cortisol associated with low pH may indicate the role of cortisol in acid-base regulation. Only the low DO (dissolved oxygen) group did not exhibit a recovery of cortisol levels by the end of one week. There was no observable difference in IGF-1 in juvenile blue rockfish after a week of exposure to any of the pH or DO stressors. When cortisol levels were high, the same fish had low levels of IGF-1, and when cortisol levels were lower, the same fish had highly variable levels of IGF-1. At one-week of exposure, cortisol exhibited a positive relationship with MMR, such that higher stress levels were associated with greater oxygen consumption by the fish. MMR values themselves were highest in the low DO fish, which subsequently also had slightly higher cortisol levels at one-week. Juvenile blue rockfish were largely robust to any behavioral changes associated with stress across treatments. Hypoxic treatment fish had significantly lower body condition than fish from treatments with ambient DO levels after one week. Overall, the results indicated that pH levels influenced hormonal stress physiology, while DO levels contributed to observed differences in metabolism, body condition, and behavioral anxiety in juvenile blue rockfish. I was unable to tease apart and classify whether OA and hypoxia work in an additive, antagonistic, or synergistic way. Continued research should include more experimental stressor treatment levels of varying intensity of both individual and combined treatments as well as upwelling/relaxation fluctuating treatment levels. Elucidating the effects of climate change on fish endocrine response and physiology is important for fish population management and can help inform stock assessment models of blue rockfish in a rapidly changing ocean.

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Effects of acidification on fish larval abundance at Teknaf coast, Bangladesh

The study aimed to investigate the effects of acidification on fish larvae abundance at the Teknaf coast. From January 8 to December 14, 2021, samples of fish larvae were collected at every month from the Teknaf coast. From the bottom to the surface, Bongo-Net with a 500 µm mesh size was being towed. A total of 1,120 larvae were gathered from the research area during the survey. In the study region, 93 larvae/1,000 m3 were found to be the mean density of all fish larvae. The hydrological parameters such as water temperature, pH, salinity, and total alkalinity were determined to find out the effects of these variables on the larvae abundance along the Teknaf coast. The average values of the parameters including water temperature, pH, salinity, and total alkalinity were found at 28.41°C, 8.36, 23.57 PSU, and 113.25 mg/l respectively. The ocean acidification factors including pCO2, HCO3-, CO32-, DIC, ΩAragonite, and ΩCalcite were also determined by using the “seacarb” package of R programming to find out the effects of these variables on the larvae abundance along the Teknaf coast. The average values of the factors including pCO2, HCO3-, CO32-, DIC, ΩAragonite, and ΩCalcite were found 128.72 µatm, 0.000751 mole/kg, 0.000138 mole/kg, 0.000892 mole/kg, 2.3544 and 3.7028 respectively. The results showed an insignificant relationship between pCO2 and fish larvae abundance throughout the Teknaf coast. However, there was a negative correlation between pCO2 and pH. The findings of this research indicate that OA affects fish larvae abundance at Teknaf coast. Regional fisheries management organizations will be better able to make decisions about the management of the extremely valuable fish larvae as a result of future population-level predictions of the impacts of ocean acidification.

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pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: metal accumulation, antioxidant defenses and biodetoxification in livers

Graphical abstract.

Highlights

  • SA and Cu interact during hepatic antioxidant defenses and biodetoxification.
  • Moderate SA helps alleviate Cu exposure-induced LPO, but extreme SA exacerbates it.
  • Thiols respond actively to cope with Cu toxicity in acidified seawater.
  • SOD, CAT, EROD and GST sensitively respond to SA and Cu coexposure.
  • Pearson’s correlation coefficient and PCA usefully integrate biomarker responses.

Abstract

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO2-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L−1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO2 ∼1353.89 μatm; extreme SA: pH 7.30, pCO2 ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and biodetoxification in response to coexposure. Hepatic Cu accumulation (30.22–184.90 mg kg−1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and biodetoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

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Impacts of global environmental change on fish and fisheries of the Northeastern Pacific Ocean

Marine fishes’ intolerance to global change conditions can affect the abundance and distribution of ecologically and economically important species, reshape the structure of trophic webs, and profoundly impact the human communities that rely on fished species for their livelihood and culture. Only by understanding the vulnerability of fished species and fishing communities to global change can we take effective adaptive action and implement climate-ready fisheries management. In this dissertation, I investigate the vulnerability of eight commercially important fished species and one fishing community to global change in the Northeastern Pacific Ocean. In chapter one, I expose Lingcod (Ophiodon elongatus), a benthic egg layer, to temperature, oxygen, and pH conditions we expect to see in the Central California Current System (CCS) by the year 2050 and 2100. I examine both the lethal and sublethal effects of these two multistressor climate change scenarios by measuring differences in metabolic rate, hatching success, and larval quality between treatments. In chapter two, I use a species distribution modeling approach to evaluate how historical (1982-2019) and projected (2030 through end-of-century) warming in the Eastern Bering Sea (EBS), Alaska, affects predator-prey interactions for some of the most commercially valuable fisheries in the U.S. These species include: 1) Pacific Cod (Gadus macrocephalus), 2) Pacific Halibut (Hippoglossus stenolepis), 3) Arrowtooth Flounder, 4) Walleye Pollock (Gadus chalcogrammus), 5) Tanner Crab (Chionoecetes bairdi), 6) Snow Crab (Chionoecetes opilio), and 7) Alaskan Pink Shrimp (Pandalus eous). In chapter three, I use social network analyses to depict the resilience and adaptability of the California Market Squid fishery (Doryteuthis opalescens), the most valuable in the state, to climate perturbations and project changes in habitat suitability by the year 2100 in the CCS. By using all of these vulnerability assessment tools, we can begin to prepare U.S. west coast fisheries for global environmental change.

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Ocean acidification alters the acute stress response of a marine fish

Graphical abstract.

Highlights

  • Ocean acidification (OA) impacts the physiological stress response of European sea bass.
  • Post-stress return to basal plasma cortisol and glucose levels is delayed under OA.
  • This delay is associated to alteration of hypothalamic neurotransmitters pattern.
  • Motor activity is reduced during recovery from stress in fish under OA conditions.

Abstract

The absorption of anthropogenic carbon dioxide from the atmosphere by oceans generates rapid changes in seawater carbonate system and pH, a process termed ocean acidification. Exposure to acidified water can impact the allostatic load of marine organism as the acclimation to suboptimal environments requires physiological adaptive responses that are energetically costly. As a consequence, fish facing ocean acidification may experience alterations of their stress response and a compromised ability to cope with additional stress, which may impact individuals’ life traits and ultimately their fitness. In this context, we carried out an integrative study investigating the impact of ocean acidification on the physiological and behavioral stress responses to an acute stress in juvenile European sea bass. Fish were long term (11 months) exposed to present day pH/CO2 condition or acidified water as predicted by IPCC “business as usual” (RCP8.5) scenario for 2100 and subjected to netting stress (fish transfer and confinement test). Fish acclimated to acidified condition showed slower post stress return to plasma basal concentrations of cortisol and glucose. We found no clear indication of regulation in the central and interrenal tissues of the expression levels of gluco- and mineralocorticoid receptors and corticoid releasing factor. At 120 min post stress, sea bass acclimated to acidified water had divergent neurotransmitters concentrations pattern in the hypothalamus (higher serotonin levels and lower GABA and dopamine levels) and a reduction in motor activity. Our experimental data indicate that ocean acidification alters the physiological response to acute stress in European sea bass via the neuroendocrine regulation of the corticotropic axis, a response associated to an alteration of the motor behavioral profile. Overall, this study suggests that behavioral and physiological adaptive response to climate changes related constraints may impact fish resilience to further stressful events.

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Coral reef fishes in a multi-stressor world

Coral reef fishes and the ecosystems they support represent some of the most biodiverse and productive ecosystems on the planet yet are under threat as they face dramatic increases in multiple, interacting stressors that are largely intensified by anthropogenic influences, such as climate change. Coral reef fishes have been the topic of 875 studies between 1979 and 2020 examining physiological responses to various abiotic and biotic stressors. Here, we highlight the current state of knowledge regarding coral reef fishes’ responses to eight key abiotic stressors (i.e., pollutants, temperature, hypoxia and ocean deoxygenation, pH/CO2, noise, salinity, pressure/depth, and turbidity) and four key biotic stressors (i.e., prey abundance, predator threats, parasites, and disease) and discuss stressors that have been examined in combination. We conclude with a horizon scan to discuss acclimation and adaptation, technological advances, knowledge gaps, and the future of physiological research on coral reef fishes. As we proceed through this new epoch, the Anthropocene, it is critical that the scientific and general communities work to recognize the issues that various habitats and ecosystems, such as coral reefs and the fishes that depend on and support them, are facing so that mitigation strategies can be implemented to protect biodiversity and ecosystem health.

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Genetic architecture of behavioural resilience to ocean acidification

Genetic variation is essential for adaptation to rapid environmental changes. Identifying genetic variation associated with climate-change related phenotypes is therefore the necessary first step towards predictive models of genomic vulnerability.

Here we used a whole-genome scan to identify candidate genetic variants associated with differences in behavioural resilience to ocean acidification in a coral reef fish. We identified three genomic regions that differ between individuals that are behaviourally tolerant compared with behaviourally sensitive to elevated CO2. These include a dopamine receptor (drd4rs), cadherin related family member 5-like (cdhr5l), Synapse-associated protein 1 (syap1), and GRB2 Associated Regulator of MAPK1 Subtype 2 (garem2), which have previously been found to modify behaviour related to boldness, novelty seeking, and learning in other species, and differ between behaviourally tolerant and sensitive individuals.

Consequently, the identified genes are promising candidates in the search of the genetic underpinnings and adaptive potential of behavioural resilience to ocean acidification in fishes.

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Lack of detrimental effects of ocean acidification and warming on proximate composition, fitness and energy budget of juvenile Senegalese sole (Solea senegalensis)

Graphical abstract.

Highlights

  • Climate change can affect nutritional quality and physiology of marine organisms.
  • Growth, metabolism and excretion were assessed under acidification and warming.
  • Weight gain, metabolic rates and energy intake increased under future climate conditions.
  • The highest energy budget fractions were allocated to growth and faecal excretion.
  • Juvenile Senegalese sole is resilient to climate change-related scenarios.

Abstract

Rising levels of atmospheric carbon dioxide (CO2) are driving ocean warming and acidification, which may negatively affect the nutritional quality and physiological performance of commercially important fish species. Thus, this study aimed to evaluate the effects of ocean acidification (OA; ΔpH = −0.3 units equivalent to ΔpCO2 ~ +600 μatm) and warming (OW; ΔT = +4 °C) (and combined, OAW) on the proximate composition, fitness and energy budget of juvenile Senegalese sole (Solea senegalensis). After an exposure period of 75 days, growth (G), metabolism (R) and excretion (faecal, F and nitrogenous losses, U) were assessed to calculate the energy intake (C). Biometric and viscera weight data were also registered to determine animal fitness. Overall, the proximate composition and gross energy were not significantly affected by acidification and warming (alone or in combination). Weight gain, maximum and standard metabolic rates (MMR and SMR, respectively), aerobic scope (AS) and C were significantly higher in fish subjected to OA, OW and OAW than in CTR conditions. Furthermore, the highest relative growth rates (RGR), specific growth rates in terms of wet weight (SGRw) and protein (SGRp), as well as feed efficiencies (FE) occurred in fish submitted to OW and OAW. On the other hand, fish exposed to CTR conditions had significantly higher feed conversion ratio (FCR) and ammonia excretion rate (AER) than those exposed to simulated stressors. Regarding energy distribution, the highest fraction was generally allocated to growth (48–63 %), followed by excretion through faeces (36–51 %), respiration (approximately 1 %) and ammonia excretion (0.1–0.2 %) in all treatments. Therefore, ocean warming and acidification can trigger physiological responses in juvenile Senegalese sole, particularly in their energy budget, which can affect the energy flow and allocation of its population. However, and in general, this species seems highly resilient to these predicted ocean climate change stressors.

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Immunomodulatory response of Asian seabass Lates calcarifer in an ex situ environment: implications for future ocean acidification scenario

Global warming and ocean acidification (OA) are being brought on by an increase in atmospheric carbon dioxide (CO2) concentration (Feely et al., 2004Orr et al., 2005), and both are now widely acknowledged as significant factors in modulating physiological systems in the marine organism (Srinivasan et al., 2022). Increased CO2 levels in the surface waters result in a drop in seawater pH, and changes in the chemistry of carbonates, and can have an impact on the bioavailability of contaminants (Bijma et al., 2013). Although OA has a significant impact on the acid-base balance, energy metabolism, and biomineralization of marine organisms (Kroeker et al., 2010), its effects on immune functions are still poorly understood (Calder-Potts et al., 2008), which makes it difficult to predict how susceptible marine fish to overcome the parasites and diseases attack as the ocean physicochemical concentration changes.

The survival of marine organisms are significantly influenced by good seawater quality (Jha et al., 2013), diseases and parasites free suitable locations, which are regarded as the main risk factor in both fish farms and the open ocean (Kumar et al., 2009Jha et al., 2017). The resistance of aquatic organisms to parasites and diseases can be modulated by environmental stresses, such as fluctuations in temperature, salinity, and pollution (Galloway and Depledge, 2001Marcogliese, 2008). Fish that live in water are constantly exposed to a variety of pathogenic and non-pathogenic microorganisms; as a result, they may evolve powerful defence systems that aid in their survival. Aquatic organism immune systems, like that of fish, are constantly impacted by periodic or unanticipated changes in their surroundings. Fish health status may be negatively impacted by adverse environmental circumstances either acutely or chronically, either by changing certain biochemical parameters or by regulating innate and adaptive immune responses (Domingueza et al., 2004). Fish may therefore serve as significant indicator in the biomonitoring of water quality, particularly immunotoxic environmental contaminants, depending on their biological factors related to immunity.

The available literature regarding the alteration of immunity in shellfish because of ocean acidification shows that earlier studies were focused on marine invertebrates since the shellfish are more vulnerable to acidified environment since most of the higher invertebrates rely more on these environment for calcification (Ivanina et al., 2014). Our previous study documented that acidified environment impairs haematological and serum biochemical parameters in Lates calcarifer (Srinivasan et al., 2022). In the present study, it was further observed that long-term chronic exposure to acidified medium modulated the immunocompetence of fish in terms of the change in immune-associated parameters tested. To our knowledge, negligible work has been carried out to observe the impact of seawater acidification on immunomodulation in fish with different size groups. Therefore the present study investigated the effect of acidification on the nonspecific immune-associated parameters, including respiratory burst, myeloperoxidase (MPO) activity, bactericidal activity, circulating total immunoglobulin, and on cellular components (leukocytes) in two different size groups (fish fry and fingerlings) of Lates calcarifer.

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Ocean acidification and seasonal temperature extremes combine to impair the thermal physiology of a sub-Antarctic fish

Graphical abstract

Highlights

  • Climate change stressors impaired the thermal physiology of Eleginops maclovinus.
  • Summer temperature and near-future pCO2 levels reduced its thermal tolerance.
  • Concomitant reductions occurred in fish aerobic scope at near-future pCO2.
  • An oxidative stress condition was detected in the gills and liver tissues.

Abstract

To predict the potential impacts of climate change on marine organisms, it is critical to understand how multiple stressors constrain the physiology and distribution of species. We evaluated the effects of seasonal changes in seawater temperature and near-future ocean acidification (OA) on organismal and sub-organismal traits associated with the thermal performance of Eleginops maclovinus, a sub-Antarctic notothenioid species with economic importance to sport and artisanal fisheries in southern South America. Juveniles were exposed to mean winter and summer sea surface temperatures (4 and 10 °C) at present-day and near-future pCO2 levels (~500 and 1800 μatm). After a month, the Critical Thermal maximum and minimum (CTmax, CTmin) of fish were measured using the Critical Thermal Methodology and the aerobic scope of fish was measured based on the difference between their maximal and standard rates determined from intermittent flow respirometry. Lipid peroxidation and the antioxidant capacity were also quantified to estimate the oxidative damage potentially caused to gill and liver tissue. Although CTmax and CTmin were higher in individuals acclimated to summer versus winter temperatures, the increase in CTmax was minimal in juveniles exposed to the near-future compared to present-day pCO2 levels (there was a significant interaction between temperature and pCO2 on CTmax). The reduction in the thermal tolerance range under summer temperatures and near-future OA conditions was associated with a reduction in the aerobic scope observed at the elevated pCO2 level. Moreover, an oxidative stress condition was detected in the gill and liver tissues. Thus, chronic exposure to OA and the current summer temperatures pose limits to the thermal performance of juvenile E. maclovinus at the organismal and sub-organismal levels, making this species vulnerable to projected climate-driven warming.

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Limited behavioural effects of ocean acidification on a Mediterranean anemone goby (Gobius incognitus) chronically exposed to elevated CO2 levels

Graphical abstract

Highlights

  • This is the first assessment in the wild of behavioural responses of fish acutely and chronically exposed to elevated CO2.
  • High density of anemone goby fish was recorded at high-CO2 levels off a volcanic CO2 vent in Vulcano island (Italy).
  • Acute and chronic exposure to elevated CO2 did not affect most of the behaviours in adult G. incognitus.
  • Behavioural plasticity occurred under ocean acidification conditions suggesting potential local adaptation.

Abstract

An in situ reciprocal transplant experiment was carried around a volcanic CO2 vent to evaluate the anti-predator responses of an anemone goby species exposed to ambient (∼380 μatm) and high (∼850 μatm) CO2 sites. Overall, the anemone gobies displayed largely unaffected behaviors under high-CO2 conditions suggesting an adaptive potential of Gobius incognitus to ocean acidification (OA) conditions. This is also supported by its 3-fold higher density recorded in the field under high CO2. However, while fish exposed to ambient conditions showed an expected reduction in the swimming activity in the proximity of the predator between the pre- and post-exposure period, no such changes were detected in any of the other treatments where fish experienced acute and long-term high CO2. This may suggest an OA effect on the goby antipredator strategy. Our findings contribute to the ongoing debate over the need for realistic predictions of the impacts of expected increased CO2 concentration on fish, providing evidence from a natural high CO2 system.

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Saving Nemo: extinction risk, conservation status, and effective management strategies for anemonefishes

Anemonefishes share a number of life history and ecological traits, and some unfortunate links to human-induced stress, that expose some of the 28 species to the risk of extinction. The biodiversity hotspot for anemonefishes extends across Southeast Asia to the western Pacific, including many countries where there are high levels of human impact and few effective management strategies. Anemonefish biodiversity is threatened by anemone bleaching, direct effects of ocean warming and acidification, collection for the aquarium trade, and coastal development. These risks are exacerbated by extreme habitat specialization, the mutual anemonefish–anemone relationship, low abundance, low population connectivity, small geographic ranges, and shallow depth ranges. Many species exhibit two or three of these traits, with small range species often associated with fewer anemone hosts and narrower depth ranges, exposing them to double or triple jeopardy. While all species have not been assessed by the IUCN, our detailed analysis of area of occupancy indicates that three species are extremely close to the threshold for being classified as Critically Endangered. Marine reserves have been effective in protecting species from exploitation and helping sustain marginal populations across generations, but effective population sizes are often very small and recovery can be slow. Additional management efforts need to focus on sustainable collecting practices and the protection and restoration of critical anemone habitats.

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Vulnerability of exploited deep-sea demersal species to ocean warming, deoxygenation, and acidification

Vulnerability of marine species to climate change (including ocean acidification, deoxygenation, and associated changes in food supply) depends on species’ ecological and biological characteristics. Most existing assessments focus on coastal species but systematic analysis of climate vulnerability for the deep sea is lacking. Here, we combine a fuzzy logic expert system with species biogeographical data to assess the risks of climate impacts to the population viability of 32 species of exploited demersal deep-sea species across the global ocean. Climatic hazards are projected to emerge from historical variabilities in all the recorded habitats of the studied species by the mid-twenty-first century. Species that are both at very high risk of climate impacts and highly vulnerable to fishing include Antarctic toothfish (Dissostichus mawsoni), rose fish (Sebastes norvegicus), roughhead grenadier (Macrourus berglax), Baird’s slickhead (Alepocephalus bairdii), cusk (Brosme brosme), and Portuguese dogfish (Centroscymnus coelepis). Most exploited deep-sea fishes are likely to be at higher risk of local, or even global, extinction than previously assessed because of their high vulnerability to both climate change and fishing. Spatially, a high concentration of deep-sea species that are climate vulnerable is predicted in the northern Atlantic Ocean and the Indo-Pacific region. Aligning carbon mitigation with improved fisheries management offers opportunities for overall risk reduction in the coming decades. Regional fisheries management organizations (RFMOs) have an obligation to incorporate climate change in their deliberations. In addition, deep-sea areas that are not currently managed by RFMOs should be included in existing or new international governance institutions or arrangements.

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The effects of ocean acidification and temperature rise on the thermal tolerance and critical thermal limit of Pacific herring (Clupea pallasii)

Anthropogenic climate change, including the interactive effects of ocean acidification and temperature rise, is projected to affect marine ecosystems by challenging the environmental tolerance limits of individual species. Such impacts have been documented in a handful of marine fishes, including major physiological effects experienced in early-life stages of Pacific herring, an important forage and commercial fish species widely distributed in coastal systems across the North Pacific. In this study, we investigated the effects of temperatures between 10-16°C and two pCO2 levels (ambient and high pCO2) on hatching and survival of Pacific herring. Survival after acute temperature exposure was assessed and compared between incubation treatments, as may be experienced by herring egg deposits during low tide on warm days. We compared early and late spawning populations to determine if their responses differed when exposed to chronic temperature and pCO2 conditions and to short term temperature stress. A subset of embryos from the 10°C and 16°C treatments were exposed to critical thermal maximum (𝐶𝑇𝑚𝑎𝑥) trials that simulated the acute temperature fluctuations associated with marine heat waves and tidal processes in shallow nearshore habitats. Hatching success was primarily influenced by temperature in both winter and spring embryos. 𝐶𝑇𝑚𝑎𝑥 results indicate that embryos were able to withstand acute exposure to 20°C regardless of spawning population or incubation treatments, but survival was greatly reduced after 2-3 hours at 25°C. Post-exposure heart contraction measurements revealed a greater rate of increase in heart rate in the combined treatment of 10°C and 𝐶𝑇𝑚𝑎𝑥 duration hours compared to 16°C, suggesting respiratory acclimation at higher incubation temperatures. Oxygen consumption rates (MO2) measured at stable incubation conditions resulted in higher MO2 values at elevated temperatures and pCO2 levels. Overall, this study reinforces that Pacific herring are resilient to moderate pCO2 and temperature stress but are vulnerable to acute temperature increases that may accompany marine heatwave events and late season low tide temperatures, and in some cases the combination of elevated pCO2 and temperature can introduce additional challenges for these important forage fish.

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The effects of low pH and high water temperature on oxidative stress and cell damage in juvenile olive flounder Paralichthys olivaceus: comparison of single and combined environmental conditions

  • Correction to this article was published on 02 September 2022
  • This article has been updated

The use of fossil fuels by anthropogenic activities causes ocean acidification and warming, and these changes in the marine environment can negatively affect the metabolism, growth, and survival of fish. In the present study, we evaluated the ability of olive flounder Paralichthys olivaceus to cope with future marine environmental changes by investigating the oxidative stress (cortisol, HSP70), antioxidant enzyme (superoxide dismutase; SOD, catalase; CAT) activity, and apoptosis (caspase-3) after exposure to control conditions (20 °C and pH 8.1), warming (30 °C) and acidification (pH 7.5) conditions, and a combined environment (30 °C and pH 7.5) for 28 days. Under warming conditions, increased oxidative stress, activity of antioxidant enzymes, and apoptosis were observed. Acidifying conditions showed negative effects at the beginning of exposure, but these effects were offset over time. Even in a combined environment of acidification and warming, negative effects were seen only at the beginning of exposure and were not sustained. In conclusion, the effects of acidification on oxidative stress, antioxidant response, and apoptosis in Polivaceus did not exceed the effects of warming. These results suggest that P. olivaceus can cope with the predicted future acidifying environment.

Continue reading ‘The effects of low pH and high water temperature on oxidative stress and cell damage in juvenile olive flounder Paralichthys olivaceus: comparison of single and combined environmental conditions’

Selection on offspring size and contemporary evolution under ocean acidification

Ocean acidification may have deleterious effects on many species, but anticipating long-term changes in the abundance of populations will require an understanding of ocean acidification as an evolutionary force. Here, I show that ocean acidification alters natural selection on offspring size and is likely to drive contemporary evolution. In a detailed study of a coastal fish species (California grunion), I demonstrate that larval mortality is highly sensitive to ocean acidification and that mortality rates are lower for larger larvae. However, these effects are countered by tradeoffs between offspring size and number, suggesting that measurements of maternal fitness are critical for quantifying selection through ocean acidification. Measurements of selection and genetic variation were used to project the evolution of larval size as seawater conditions changed incrementally over many decades. Results for California grunion suggest that contemporary evolution may offset the projected decline in reproductive success by about 50%.

Continue reading ‘Selection on offspring size and contemporary evolution under ocean acidification’

Impacts of ocean warming and acidification on the energy budget of three commercially important fish species

Using experimental data of three commercially important marine fish species (Diplodus sargus, Diplodus cervinus and Solea senegalensis), a model based on Dynamic Energy Budget theory was parametrized. The model was used to produce projections of growth and reproduction for these species, under different scenarios of ocean warming and acidification.

A mechanistic model based on Dynamic Energy Budget (DEB) theory was developed to predict the combined effects of ocean warming, acidification and decreased food availability on growth and reproduction of three commercially important marine fish species: white seabream (Diplodus sargus), zebra seabream (Diplodus cervinus) and Senegalese sole (Solea senegalensis). Model simulations used a parameter set for each species, estimated by the Add-my-Pet method using data from laboratory experiments complemented with bibliographic sources. An acidification stress factor was added as a modifier of the somatic maintenance costs and estimated for each species to quantify the effect of a decrease in pH from 8.0 to 7.4 (white seabream) or 7.7 (zebra seabream and Senegalese sole). The model was used to project total length of individuals along their usual lifespan and number of eggs produced by an adult individual within one year, under different climate change scenarios for the end of the 21st century. For the Intergovernmental Panel on Climate Change SSP5-8.5, ocean warming led to higher growth rates during the first years of development, as well as an increase of 32-34% in egg production, for the three species. Ocean acidification contributed to reduced growth for white seabream and Senegalese sole and a small increase for zebra seabream, as well as a decrease in egg production of 48-52% and 14-33% for white seabream and Senegalese sole, respectively, and an increase of 4-5% for zebra seabream. The combined effect of ocean warming and acidification is strongly dependent on the decrease of food availability, which leads to significant reduction in growth and egg production. This is the first study to assess the combined effects of ocean warming and acidification using DEB models on fish, therefore, further research is needed for a better understanding of these climate change-related effects among different taxonomic groups and species.

Continue reading ‘Impacts of ocean warming and acidification on the energy budget of three commercially important fish species’

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