Posts Tagged 'fish'

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Olfactory specialization in the Senegalese sole (Solea senegalensis): CO2 acidified water triggers nostril-specific immune processes

Published 10 February 2025 Science Closed
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Highlights

  • Exposure to high PCO2/low pH water decreases olfactory sensitivity in sole more markedly in the upper olfactory epithelium (OE).
  • Resilience of the lower OE may be linked to exposure to a different environment.
  • Regulation of genes related to neuromodulation and neuroplasticity suggests activation of compensatory mechanisms.
  • Regulation of immune processes related genes together with histological modifications will likely compromise olfactory sensitivity with behavioural consequences.
  • Ocean acidification has effects on the peripheral nervous system at various levels.

Abstract

Increased carbon dioxide (CO2) in the ocean is changing seawater chemistry. Behavioural alterations in CO2 exposed fish have been linked to changes in the central nervous system (CNS). However, we hypothesise that receptor cells in direct contact with the environment are more susceptible to changes in water chemistry than the CNS. Electrophysiology, histology, and transcriptomics were used to explore the effect of exposure to CO2 acidified water on the olfactory epithelium (OE) of the Senegalese sole (Solea senegalensis). The upper and lower OE of this flatfish detect different odorants and are in contact with different environments. Acute exposure to acidified water decreased olfactory sensitivity more in the upper than in the lower OE. After chronic exposure to high CO2 there was no histological changes in the upper OE, however, in the lower OE, there was a massive infiltration of melanomacrophage (MMC) and tissue disorganization. In addition, in the upper OE, differential expressed gene transcripts (DETs) were related to inflammation and innate immune processes whereas in the lower OE, DETs were related to the adaptative immune response. Differential regulation of genes related to neurogenesis and plasticity occurred in both epithelia.

The effects of ocean acidification in sole OE depends on the nostril, however the occurrence of an exacerbated immune response, OE remodelling and reduced sensitivity indicate that ocean acidification is likely to have significant and unpredictable consequences for behaviour.

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Warming, but not acidification, increases metabolism and reduces growth of redfish (Sebastes fasciatus) in the Gulf of St. Lawrence

Published 6 February 2025 Science Closed
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Understanding the effects of global change, including temperature, pH, and oxygen availability, on commercially important species is crucial for anticipating consequences for these resources and their ecosystems. In the Gulf of St. Lawrence (GSL), redfish (Sebastes spp.) have been under moratorium from 1995 to 2024, with a massive recruitment observed in 2011–2013. However, little is known about their metabolic and thermal physiology, making predictions of their response to changing GSL conditions challenging. To address this, we quantified the effects of four acclimatation temperatures (2.5, 5.0, 7.5, and 10.0 ℃) and two pH levels (7.35 and 7.75) on standard and maximum metabolic rates (SMR and MMR), aerobic scope (AS), hypoxia tolerance (O2crit), food consumption, and growth in redfish. SMR, MMR, and AS increased with temperature, but growth decreased at the highest temperature, likely due to increased metabolic demand, with food consumption similar across 5.0 to 10.0 °C treatments. O2crit was lower for fish acclimated to 2.5 and 5.0 ℃, making redfish less hypoxia-tolerant at higher temperatures. Except from SMR, no significant effect of pH was observed. These results suggest that future changes in the GSL will challenge redfish, with potential long-term effects on their growth due to increased energy requirements.

Continue reading ‘Warming, but not acidification, increases metabolism and reduces growth of redfish (Sebastes fasciatus) in the Gulf of St. Lawrence’

Molecular and physiological responses of black rockfish (Sebastes schlegelii) to short- and medium-term ocean acidification

Published 5 February 2025 Science Closed
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Ocean acidification (OA) is one of the greatest threats to marine species, with widespread impacts on their physiological functions. However, the adaptive capacities of many marine species to OA and the underlying mechanisms remain unclear. In this study, we investigated the effects of short-term (4 days) and medium-term (30 days) CO2 exposure (pH 8.0, 7.6, and 7.3) on black rockfish (Sebastes schlegelii), focusing on histopathological changes in gill tissues, ion transport biomarkers, oxidative stress indicators, and transcriptomic responses. The results showed that both short-term and medium-term OA induced significant morphological changes in gill tissues, including epithelial lifting, hyperplasia, hypertrophy, and lamellar clubbing, which are likely adaptive mechanisms for maintaining homeostasis. Both Na+/K+-ATPase and carbonic anhydrase (CA) activities increased significantly in both short- and medium-term exposure, while Ca2+-ATPase activity was elevated only in the short-term, suggesting differential enzyme regulation over time to sustain ionic balance. Additionally, oxidative stress indicators (superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), reduced glutathione (GSH) and glutathione peroxidase (GPx)) were significantly elevated after both exposure durations, indicating that the antioxidant defense system was activated. Moreover, the integrated biomarker response (IBR) index further indicated that the stress response was more pronounced during short-term exposure. Transcriptomic analysis reveals significant alterations in pathways related to calcium signaling, cytoskeletal structure, energy metabolism, and oxidative stress following short-term exposure. In contrast, medium-term exposure leads to significant enrichment of pathways associated with cell-environment interactions, highlighting the molecular adaptations of S. schlegelii to OA-induced stress. These findings provide valuable insights into the mechanisms of OA tolerance in S. schlegelii and contribute to understanding the adaptability of marine species in future ocean environments.

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Climate change impacts and future risk on UK seahorse species, short-snouted Hippocampus hippocampus and long-snouted Hippocampus guttulatus

Published 7 January 2025 Science Closed
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For the two European seahorse species, the short-snouted Hippocampus hippocampus and the long-snouted Hippocampus guttulatus, there are knowledge gaps that need further research. These research gaps become increasingly pressing under climate change, where uncertainty in how coastal ecosystems will change is compounded by uncertainty in how these seahorses will respond to changing pressures. Under climate change, these species could experience northward range shifts, expanding their range in United Kingdom (UK) coastal waters, potentially requiring the UK to take a leadership role in European seahorse conservation in the future. This review aims to synthesise current scientific research to provide an overview of how these seahorse species are likely to respond to climate change. Using the most recent Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6), predictions for future change along with the likelihood and severity of seahorse species response are combined to provide a confidence ranking in the climate change risk for these species in the UK. When considering individual factors, such as sea surface temperature, these seahorse species show some resilience, but climate change is the cumulative impact of multiple stressors, which existing research has not been able to capture. Overall, further research on seahorse response to environmental variables is needed across Europe.

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Environmental determinants of reef fish community structure in Sempu Strait, East Java, Indonesia

Published 31 December 2024 Science Closed
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The Rumah Apung located in Sempu Strait, Malang District, East Java, Indonesia, is home to diverse coral reef ecosystems that provide vital ecological services and support local livelihoods. However, these ecosystems face significant threats from both natural environmental changes and anthropogenic activities. Understanding how environmental factors influence reef fish communities is critical to inform effective conservation strategies. This study investigated the influence of environmental factors on the community structure of coral reef fish in the Sempu Strait waters, East Java, using Underwater Visual Census (UVC) and Principal Component Analysis (PCA). Conducted from August 2023 to May 2024 at the Sempu Strait Floating House Station, this study aimed to assess the impact of water quality, substrate type, and food availability on the diversity and abundance of coral reef fish. The main results revealed a significant correlation between the community structure of coral reef fish and environmental variables such as water clarity, salinity (r=0.65, p<0.01), pH (r=0.55, p<0.05), dissolved oxygen (r=0.70, p<0.01), and sediment type. Seasonal variations significantly affected water quality, with cold nutrient-rich water during the east monsoon increasing fish biomass by about 30%. Human activities, especially recreational diving and fishing activities, were correlated with a 20% decline in coral reef fish populations, highlighting the anthropogenic pressure on this ecosystem. PCA provides insight into the complex interdependencies within coral reef ecosystems, illustrating how multiple environmental factors combine to influence reef fish dynamics. The study concludes that effective management and conservation strategies,such as establishing marine protected areas, implementing community-based monitoring programs, and promoting sustainable tourism practices, are essential, supported by regular environmental monitoring, are essential to maintain the biodiversity and ecological integrity of coral reefs in the Sempu Strait. These strategies should address both natural environmental changes and anthropogenic impacts to mitigate their adverse effects on coral reef ecosystem conditions.

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Climate covariate choice and uncertainty in projecting species range shifts: a case study in the Eastern Bering Sea

Published 26 December 2024 Science Closed
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Species distribution models (SDMs) are critical to the adaptive management of fisheries under climate change. While many approaches projecting marine species range shifts have incorporated the effects of temperature on movement, there is a need to incorporate a wider suite of ecologically relevant predictors as temperature-based SDMs can considerably under- or over-estimate the rate of species responses to climate shocks. As a subarctic ecosystem at the sea ice margin, the Eastern Bering Sea (EBS) is warming faster than much of the global ocean, resulting in the rapid redistribution of key fishery and subsistence resources. To support long-term planning and adaptation, we combine 40 years of scientific surveys with a high-resolution oceanographic model to examine the effects of bottom temperature, oxygen, pH and a regional climate index (the extent of the EBS ‘cold pool’) on range projections through the end of the century. We use multimodel inference to partition uncertainty among earth systems models, climate scenarios and distribution model parameterizations for several ecologically and economically important EBS groundfish and crabs. Covariate choice is the primary source of uncertainty for most species, with models that account for spatial responses to the cold pool performing better and suggesting more extensive northward movements than alternative models. Models suggest declines in the probability of occurrence at low pH and oxygen concentrations for most species. We project shifts that are directionally consistent with, yet larger than those previously estimated for most species, suggesting that accounting for large-scale climate variability in species distribution models may substantially alter range projections.

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Impact of ocean acidification on marker enzymes in Asian seabass Lates calcarifer

Published 19 December 2024 Science Closed
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Backgrounds: The influence of ocean acidification (OA) is particularly significant on calcifying organisms in marine environment. A possible explanation for acidification-induced changes in fish behaviour is that acidification interferes with marker enzymes in the liver, muscle and brain. Under a range of severe environmental circumstances, marine organisms can be susceptible to oxidative stress and results in the changes in the biochemical components which can be assessed to know the health status of organisms.

Aim of the Works: The aim of this study is to observe the impact of ocean acidification in Asian seabass Lates calcarifer and to employ a large number of biomarker to discover distinct and unique patterns. For this the fingerlings of L. calcarifer were exposed to OA, in order to understand the changes in marker enzymes in liver, muscle and brain of L. calcarifer.

Methodology: Fish fingerlings were exposed to OA condition with two different pH (7.8 and 7.5) for a period of 9 weeks in order to assess changes in biomarker. Acid phosphatase (ACP) and alkaline phosphatase (ALP), alanine transaminase (ALT), and aspartate transaminase activity (AST) were examined in the liver, brain and muscles of fish.

Results: The Liver has considerably higher in ACP and ALP enzymes after 3 weeks of OA exposure. AST and ALT marker enzymes were induced in the brain at greater levels and in most cases, the entire marker enzymes in the liver, muscle and brain were concentration dependent and also the exposure period. The observed changes in marker enzymes which detected in the brain and liver tissues of L. calcarifer were statistically significant.

Conclusions: The present study showed a significant association between the entire biomarkers tested in fish exposed to OA. Overall, the results indicate that brain and liver is the most vulnerable component to OA exposure when compared to muscles and brain it may be employed as a bioindicator of OA exposure.

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Cross-talk between tissues is critical for intergenerational acclimation to environmental change in Acanthochromis polyacanthus

Published 21 November 2024 Science Closed
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Organisms’ responses to environmental changes involve complex, coordinated responses of multiple tissues and potential parental influences. Here using a multi-tissue approach we determine how variation in parental behavioural tolerance and exposure to elevated CO2 influences the developmental and intergenerational molecular responses of their offspring in the coral reef fish Acanthochromis polyacanthus to future ocean acidification (OA) conditions. Gills and liver showed the highest transcriptional response to OA in juvenile fish regardless of parental OA conditioning, while the brain and liver showed the greatest intergenerational acclimation signals. Developmentally induced signals of OA, such as altered neural function in the brain, were restored to control levels after intergenerational exposure. Intergenerational CO2 exposure also enabled the offspring to adjust their metabolic processes, potentially allowing them to better meet the energetic demands of a high CO2 environment. Furthermore, offspring of OA-exposed parents differentially expressed a new complement of genes, which may facilitate intergenerational acclimatory responses. A genetic component of intergenerational plasticity also played a crucial role, with the parental behavioural phenotype largely determining the offspring’s transcriptional signals. Overall, our results reveal tissue-specific transcriptional changes underlying intergenerational plastic responses to elevated CO2 exposure, enhancing understanding of organismal acclimation to OA throughout the whole body.

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Transcriptomic insights into the antagonistic responses of Antarctic marbled rockcod, Notothenia rossii, to elevated temperature and acidification

Published 6 November 2024 Science Closed
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Highlights

  • N. rossii exhibits complex immune reactions to warming and acidification.
  • Antagonistic gene expressions under combined environmental stressors identified.
  • Comprehensive view on N. rossii’s resilience to climate change impacts.

Abstract

The escalating impacts of climate change, particularly ocean acidification and warming, are pivotal stressors for marine ecosystems and have profound effects on biota in polar regions. This study investigated the immunological responses of the Antarctic fish Notothenia rossii to environmental stressors indicative of future ocean conditions under the Intergovernmental Panel on Climate Change Shared Socioeconomic Pathways 5–8.5 scenario for 2100. We exposed N. rossii to conditions simulating present-day conditions: control, elevated temperature, acidification, and both stressors combined over six days. Utilizing RNA-Seq for comprehensive gene expression analysis, we identified significant upregulation and downregulation of immune-related pathways, highlighting a complex interplay of genes involved in complement and coagulation cascades, the intestinal immune network for immunoglobulin A production, cytosolic DNA sensing, natural killer cell-mediated cytotoxicity, and Interleukin 17 signaling pathways. Our findings revealed a predominantly antagonistic gene expression response, suggesting an intricate balance between energy allocation for maintaining homeostasis and the capacity of the immune system to combat stressors. This reflects a potential adaptive mechanism to combined environmental stressors, underscoring the complexity of immune responses in N. rossii and suggesting both potential vulnerabilities and resilience in the face of climate change. This study provides critical insights into the immunological impacts of acidification and warming on Antarctic marine species, emphasizing the need for further research to unravel the mechanisms underlying these observed changes and inform conservation strategies for polar ecosystems in a changing global climate.

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Effects of ocean warming with stable and fluctuating ocean acidification on seawater transition in Chinook salmon smolts

Published 1 November 2024 Science Closed
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Highlights

  • The effects of ocean warming and acidification are a concern for declining fish populations worldwide
  • Ecologically relevant climate change impacts on early marine migration of juvenile salmon is lacking
  • Constant and fluctuating CO2 caused an ionoregulatory disturbance in Chinook salmon smolts following seawater entry
  • Salmon were able to compensate these effects through increased expression of gill ion transporters

Abstract

Anadromous salmon populations are declining in the Pacific Northwest, with high mortality during the transition from fresh- to seawater as smolts, a stage particularly vulnerable to adverse environmental conditions. This study seeks to explore the impacts of warming and ocean acidification on the transition of life in freshwater to life at sea in Chinook salmon smolts. In a fully factorial experiment, we transitioned Chinook salmon from fresh- to seawater at current and future conditions of temperature (13 °C and 16 °C, respectively) and ocean acidification (400 and 1400 atm CO2), including a fluctuating CO2 treatment (between control and high CO2) that may be more representative of natural environmental conditions associated with upwelling and tidal cycling. We hypothesized that constant elevated CO2 levels would impair smoltification success immediately following seawater transfer, but that fluctuating conditions would be even more physiologically challenging. We predicted that elevated temperatures would exacerbate these effects. To test this, we measured plasma ion concentrations, gill Na+/K+-ATPase (NKA) isoform mRNA and protein expression, as well as condition indices in freshwater and following 1, 3, 6, and 18 days in seawater at the respective treatments. We confirmed the existence of gill freshwater and seawater isoforms of NKA (α1a and α1b, respectively) in Chinook salmon for the first time, and found an upregulation of both isoforms in the fluctuating CO2 treatment but a reduction of the number of NKA α1b cells 3-days post seawater transfer at 13 °C. At 16 °C, NKA α1b was upregulated in high CO2 levels, with an elevated hematocrit indicating fish were likely stressed. Taken together, plasma ions, gill NKA and condition indices revealed a complex response to interacting warming and acidification during the first few days in seawater, however there were no longer-term adverse physiological responses. Thus, Chinook salmon appear to be relatively resilient to near-future climate change.

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Coral reef fish visual adaptations to a changing world

Published 15 October 2024 Science Closed
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  1. Coral reef ecosystems show fluctuations in their prevailing light environment in response to both regular (e.g. between seasons) and more prevalent stochastic events (e.g. human-induced sediment runoff). In these shifting environments, phenotypic plasticity provides an essential mechanism for coral reef fishes to adjust their visual capability to meet changing sensory requirements.
  2. Here, we evaluate the growing area of research that highlights the many genetic and ecological mechanisms that affect the plastic responses of coral reef fish vision to environmental cues.
  3. With an increasing number of disturbances in the marine environment, it is critical to understand the extent and limits of visual plasticity under natural and disturbed conditions. With our current knowledge and drawing upon a large body of work in freshwater fishes, we speculate whether coral reef fishes can adapt to the changes to their visual environment and where the limitations could lie.
  4. Whilst coral reef fishes have shown visual adaptations under different light environments, the degree of plasticity is inconsistent between species. Thus, plasticity may not only be functionally significant in maintaining the performance of visually guided behaviours for single species but, more broadly, is likely key to sustaining ecosystem function.
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Could future ocean acidification be affecting the energy budgets of marine fish?

Published 14 October 2024 Science Closed
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With the unprecedented environmental changes caused by climate change including ocean acidification, it has become crucial to understand the responses and adaptive capacity of fish to better predict directional changes in the ecological landscape of the future. We conducted a systematic literature review to examine if simulated ocean acidification (sOA) could influence growth and reproduction in fish within the dynamic energy budget theory framework. As such, we chose to examine metabolic rate, locomotion, food assimilation and growth in early life stages (i.e. larvae and juvenile) and adults. Our goal was to evaluate if acclimatization to sOA has any directional changes in these traits and to explore potential implications for energetic trade-offs in these for growth and reproduction. We found that sOA had negligible effects on energetic expenditure for maintenance and aerobic metabolism due to the robust physiological capacity regulating acid–base and ion perturbations but substantive effects on locomotion, food assimilation and growth. We demonstrated evidence that sOA significantly reduced growth performance of fish in early life stages, which may have resulted from reduced food intake and digestion efficiency. Also, our results showed that sOA may enhance reproduction with increased numbers of offspring although this may come at the cost of altered reproductive behaviours or offspring fitness. While these results indicate evidence for changes in energy budgets because of physiological acclimatization to sOA, the heterogeneity of results in the literature suggests that physiological and neural mechanisms need to be clearly elucidated in future studies. Lastly, most studies on sOA have been conducted on early life stages, which necessitates that more studies should be conducted on adults to understand reproductive success and thus better predict cohort and population dynamics under ongoing climate change.

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Mutligenerational chronic exposure to near future ocean acidification in European sea bass (Dicentrarchus labrax): insights into the regulation of the transcriptome in a sensory organ involved in feed intake, the tongue

Published 10 October 2024 Science Closed
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Highlights

  • Multigenerational exposure to OA has no impact on teeth mineralization in Sea bass.
  • Of the 18703 genes expressed in the tongue, 295 exhibited OA-induced regulation.
  • Genes related to cell stress, immune system and fatty acid sensitivity are regulated.
  • OA impacts the branchial expression of p2ry4 gene involved in gustatory system.

Abstract

In this study, we examined the effect of near future ocean acidification (OA) on the transcriptome of a sensory organ in contact with surrounding water, the tongue in adult European sea bass (Dicentrarchus labrax) by mean of RNAseq experiment. We acquired a total of 14.1 Mb quality-trimmed reads covering 18,703 expressed genes from the tongue of fish reared from two generations at actual (pH 8.0 condition) and predicted near-future seawater pH (pH 7.6 condition). Gene ontologies analyses of expressed genes support the evidence that the tongue exhibits biological processes related to the sensory system, tooth mineralization and immune defences among others. Our data revealed only 295 OA-induced regulated genes with 114 up- and 181 down-regulated by OA. Functions over-represented encompass processes involved in organic substance metabolic process, RNA metabolism and especially RNA methylation which, combined with the regulation of some hsp genes expression, suggest a molecular response to stress which might contribute to lingual cell homeostasis under OA. The immune system process is also found enriched within OA-induced regulated genes. With the exception of one fatty acid receptor, known taste perception effectors were not impacted by OA in the tongue. However, a complementary droplet digital PCR approach dedicated to genes involved in gustatory signal transduction revealed the down regulation by OA of pyrimidinergic receptor (p2ry4) transcript expression in the gills of the fish. Combined with scanning electron microscopy analysis, our RNAseq data revealed that OA has no impact on processes related to teeth development and mineralization. Altogether, our data reveal that multigenerational exposure to OA has not a substantially effect on the tongue transcriptome but emphasis should be placed on investigating the potential physiological consequences related to the regulation of genes related to cell stress, immune system and fatty acid sensitivity to conclude on species resilience in face of OA.

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Vulnerability of Eastern Tropical Pacific chondrichthyan fish to climate change

Published 3 September 2024 Science Closed
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Climate change is an environmental emergency threatening species and ecosystems globally. Oceans have absorbed about 90% of anthropogenic heat and 20%–30% of the carbon emissions, resulting in ocean warming, acidification, deoxygenation, changes in ocean stratification and nutrient availability, and more severe extreme events. Given predictions of further changes, there is a critical need to understand how marine species will be affected. Here, we used an integrated risk assessment framework to evaluate the vulnerability of 132 chondrichthyans in the Eastern Tropical Pacific (ETP) to the impacts of climate change. Taking a precautionary view, we found that almost a quarter (23%) of the ETP chondrichthyan species evaluated were highly vulnerable to climate change, and much of the rest (76%) were moderately vulnerable. Most of the highly vulnerable species are batoids (77%), and a large proportion (90%) are coastal or pelagic species that use coastal habitats as nurseries. Six species of batoids were highly vulnerable in all three components of the assessment (exposure, sensitivity and adaptive capacity). This assessment indicates that coastal species, particularly those relying on inshore nursery areas are the most vulnerable to climate change. Ocean warming, in combination with acidification and potential deoxygenation, will likely have widespread effects on ETP chondrichthyan species, but coastal species may also contend with changes in freshwater inputs, salinity, and sea level rise. This climate-related vulnerability is compounded by other anthropogenic factors, such as overfishing and habitat degradation already occurring in the region. Mitigating the impacts of climate change on ETP chondrichthyans involves a range of approaches that include addressing habitat degradation, sustainability of exploitation, and species-specific actions may be required for species at higher risk. The assessment also highlighted the need to further understand climate change’s impacts on key ETP habitats and processes and identified knowledge gaps on ETP chondrichthyan species.

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Impacts of ocean acidification on marine ecosystems and mitigation strategies 

Published 30 August 2024 Science Closed
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This study explores the mechanisms of adaptation in aquatic species, including phenotypic plasticity, genetic evolution, and molecular mechanisms. Aquatic species exhibit significant phenotypic plasticity, allowing them to respond rapidly to environmental changes. Changes in gene expression related to osmoregulation and metabolic processes demonstrate how species adjust their physiological states to cope with varying conditions. Genetic evolution plays a crucial role in long-term adaptation, driven by processes such as mutation, natural selection, and genetic drift. Research shows that specific genes in marine mammals and freshwater prawns are crucial for their adaptation to aquatic environments. Molecular adaptations involve gene regulation, genomic changes, and epigenetic modifications. Studies on fireflies and marine diatoms provide insights into the genetic basis of adaptation to different environmental conditions.

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Integrated multi-biomarker responses of juvenile zebra seabream (Diplodus cervinus) to warming and acidification conditions

Published 29 August 2024 Science Closed
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The impacts of climate change-related stressors are becoming more noticeable in the ocean, particularly in coastal marine ecosystems. Yet limited information still exists on the physiological state and ecological resilience of marine fish species, especially during their early life stages (i.e., larvae and juveniles). The present study investigated the effects of chronic exposure to seawater warming (OW; ΔT = +4 °C) and acidification (OA; ΔpH = −0.3 pH units, equivalent to pCO2~1000 µatm), acting alone or combined (OWA), on juvenile zebra seabream (Diplodus cervinus) physiological resilience, considering distinct levels of biological organization (i.e., biochemical, cell, organ and individual levels). After 60 days of exposure, both stressors, in isolation or combination, significantly decreased specific growth rate (−11% in OW, −42% in OA and −49% in OWA) and leukocyte counts (from −29% in OA and OWA up to −37% in OW) in relation to the control treatment. In addition, a decreased Fulton’s condition index (K) was observed under warming and acidification in combination (−35% in OWA). At the cell level, OW, OA and OWA triggered different biomarker responses in D. cervinus (i.e., up-regulation, down-regulation, or absence of significant effect). In general, the results are suggestive of an antagonistic effect when warming and acidification are combined. OWA yielded the highest integrated biomarker response (IBR) index value in the whole organism, muscle, brain and gills of D. cervinus juveniles, therefore suggesting that the effects of these stressors are more severe when they act together. The distinct patterns observed in each stress scenario highlight the importance of carrying out further studies adjusted to the specificities of different regions, i.e., accounting not only for the type and degree of severity of environmental stressors already felt and/or projected for that specific area, but also the physiological plasticity of species that inhabit a particular ecosystem. The gathered knowledge will allow one to determine the vulnerability of particular marine species and geographic areas and, most importantly, to draw up effective and tailor-made conservation strategies to overcome climate change impacts.

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Can niche plasticity mediate species persistence under ocean acidification?

Published 27 August 2024 Science Closed
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Global change stressors can modify ecological niches of species, thereby altering ecological interactions within communities and food webs. Yet, some species might take advantage of a fast-changing environment, allowing species with high niche plasticity to thrive under climate change.

We used natural CO2 vents to test the effects of ocean acidification on niche modifications of a temperate rocky reef fish assemblage. We quantified three ecological niche traits (overlap, shift and breadth) across three key niche dimensions (trophic, habitat and behavioural).

Only one species increased its niche width along multiple niche dimensions (trophic and behavioural), shifted its niche in the remaining (habitat) was the only species to experience a highly increased density (i.e. doubling) at vents. The other three species that showed slightly increased or declining densities at vents only displayed a niche width increase in one (habitat niche) out of seven niche metrics considered. This niche modification was likely in response to habitat simplification (transition to a system dominated by turf algae) under ocean acidification.

We further showed that, at the vents, the less abundant fishes had a negligible competitive impact on the most abundant and common species. This species appeared to expand its niche space, overlapping with other species, which likely led to lower abundances of the latter under elevated CO2.

We conclude that niche plasticity across multiple dimensions could be a potential adaptation in fishes to benefit from a changing environment in a high-CO2 world.

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Effect of pH on development of the zebrafish inner ear and lateral line: comparisons between high school and university settings

Published 21 August 2024 Science Closed
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Increasing carbon dioxide levels associated with climate change will likely have a devastating effect on aquatic ecosystems. Aquatic environments sequester carbon dioxide, resulting in acidic conditions that can negatively affect fish development. Increasing climate change impacts in the coming decades will have an outsized effect on younger generations. Therefore, our research had two interconnected goals: 1) understand how aquatic acidification affects the development of zebrafish, and 2) support a high school scientist’s ability to address environmental questions of increasing importance to her generation. Working with teachers and other mentors, the first author designed and conducted the research, first in her high school, then in a university research laboratory. Zebrafish embryos were reared in varying pH conditions (6.7–8.2) for up to 7 days. We assessed fish length and development of the inner ear, including the otoliths; structures that depend on calcium carbonate for proper development. Although pH did not affect fish length, fish reared in pH 7.75 had smaller anterior otoliths, showing that pH can impact zebrafish ear development. Furthermore, we demonstrate how zebrafish may be used for high school students to pursue open-ended questions using different levels of available resources.

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Transcriptional plasticity and environmental change in marine fishes

Published 14 August 2024 Science Closed
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How organisms respond to environmental changes is crucial for their survival, especially in the face of rapid climate change. One of the mechanisms facilitating acclimation to novel environments is phenotypic plasticity, the ability of a single genotype to produce multiple phenotypes in different environments. Phenotypic plastic responses are influenced by various factors like environmental stability, parental experiences, and genetic factors and can be classified as acute, developmental, or intergenerational responses based on the timeframe involved. This dissertation investigates molecular basis of all these three types of plasticity in marine fishes in response to changes in their physical and social environment. Physical environmental changes mediated by ocean acidification negatively affects various fish species however, some thrive in naturally occurring CO2 seeps, potentially benefiting from habitat shifts induced by reduced pH levels. In the anemone goby, a species that has increased population density at CO2 seeps in Vulcano Island, Italy, differential regulation of key pathways resulting in acclimation to acidified waters, potentially mediated by developmental plasticity, were identified. While overall increase in CO2 levels elicits molecular responses in fish, the stability of CO2 concentration is crucial. Exposure of spiny damselfish to both stable and fluctuating CO2 conditions resulted in loss of natural rhythmic splicing events however, fish in fluctuating CO2 conditions alone showed increased capability of time-dependent regulation of splicing events in genes associated with synaptic plasticity and neuronal functioning. This might be mediated by the observed amplitude change in circadian rhythm genes in the fluctuating CO2 treatment enabling the fish to coordinate biological processes in anticipation of periodic changes in CO2 levels. Furthermore, the spiny damselfish showed molecular signatures of intergenerational plasticity to ocean acidification conditions, particularly in the brain and liver. Specifically, within-generation transcriptional responses indicating altered neural signaling in the brain and metabolic depression in the liver returned to control levels when parents were also exposed to elevated CO2 conditions. Interestingly, these signatures indicating intergenerational acclimation were predominant in offspring of parents behaviourally tolerant to elevated CO2 conditions. This shows that parental phenotype and parental environment play a role in mediating offspring transcriptional response to ocean acidification. An organisms’ environment encompasses not only its physical environment but also the social environment. The last chapter of this thesis explores molecular processes underlying plastic responses of organisms to changes in their social environment by using the anemone-anemonefish mutualistic system. Significant changes in the transcriptome of both species were identified during the acclimation period of mutualistic association. Anemonefish showed activation of sensory pathways in response to cues received from the anemone, while the anemone showed upregulation of genes associated with nematocyst discharge and venom production, potentially in response to sensing fish movements. This study reveals an interplay of molecular events underlying mutualistic association in both partners. Taken together, the findings reported in this thesis furthers our understanding of the molecular processes underlying various types of phenotypic plastic responses to environmental changes and provides key information regarding the acclimation potential of marine fishes to global change.

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The water content, apoptosis, and proliferation of the brain in marine medaka affected by seawater acidification

Published 8 August 2024 Science Closed
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A possible explanation for ocean acidification-induced changes in fish behavior is a systemic effect on the nervous system. Three biological barriers at the blood–brain interface effectively separate the brain from the body fluids. It is not known whether fish brain regions in contact with these barriers are affected by acidification. Here, we studied structural changes in medaka (Oryzias melastigma) brain regions contacting cerebrospinal fluid (CSF) after short-term (7 days) CO2 exposure. The brain water content decreased significantly and the superficial structure of the pia mater was changed, but there was no obvious damage to the internal structures of the brain after seawater acidification. Seawater acidification also led to an increase in apoptosis and a decrease in the number of proliferative cells in brain areas contacting CSF. These results indicate that the structure of CSF-contacting brain regions in medaka was affected by seawater acidification, and the brain responded to seawater acidification stress by increasing apoptosis and reducing proliferation.

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