Posts Tagged 'oxygen'

Acidification and hypoxia drive physiological trade-offs in oysters and partial loss of nutrient cycling capacity in oyster holobiont

Published 26 May 2023 Science Leave a Comment
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Introduction: 

Reef building oysters provide vast ecological benefits and ecosystem services. A large part of their role in driving ecological processes is mediated by the microbial communities that are associated with the oysters; together forming the oyster holobiont. While changing environmental conditions are known to alter the physiological performance of oysters, it is unclear how multiple stressors may alter the ability of the oyster holobiont to maintain its functional role.

Methods: 

Here, we exposed oysters to acidification and hypoxia to examine their physiological responses (molecular defense and immune response), changes in community structure of their associated microbial community, and changes in water nutrient concentrations to evaluate how acidification and hypoxia will alter the oyster holobiont’s ecological role.

Results: 

We found clear physiological stress in oysters exposed to acidification, hypoxia, and their combination but low mortality. However, there were different physiological trade-offs in oysters exposed to acidification or hypoxia, and the combination of stressors incited greater physiological costs (i.e., >600% increase in protein damage and drastic decrease in haemocyte counts). The microbial communities differed depending on the environment, with microbial community structure partly readjusted based on the environmental conditions. Microbes also seemed to have lost some capacity in nutrient cycling under hypoxia and multi-stressor conditions (~50% less nitrification) but not acidification.

Discussion: 

We show that the microbiota associated to the oyster can be enriched differently under climate change depending on the type of environmental change that the oyster holobiont is exposed to. In addition, it may be the primary impacts to oyster physiology which then drives changes to the associated microbial community. Therefore, we suggest the oyster holobiont may lose some of its nutrient cycling properties under hypoxia and multi-stressor conditions although the oysters can regulate their physiological processes to maintain homeostasis on the short-term.

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The effects of the “deadly trio” (warming, acidification, and deoxygenation) on fish early ontogeny

Published 11 May 2023 Science Closed
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The interaction between increased dissolved carbon dioxide, rising temperatures, and oxygen loss – the so-called “deadly trio” – is expected to strongly affect marine biota over the coming years, potentially undermining ocean services and uses. Nonetheless, no study has so far scrutinized the cumulative impact of these three stressors on fish embryonic and larval stages, known to be particularly vulnerable to environmental stress. To fill this knowledge gap, we implemented a fully multi-factorial design to investigate the effects of acute warming (Δ + 4°C; 22 ºC), acidification (Δ − 0.4 pH units; ~ 7.7 pCO2) and deoxygenation (Δ − 60% O2 saturation, ~ 3 mg O2 l− 1) over a comprehensive array of physiological (hatching success, survival rates, deformities rates, and heart rates) and behavioural responses (larvae responsiveness and phototaxis) across the early ontogeny of the temperate gilthead seabream (Sparus aurata). Deoxygenation was the main driver of negative impacts in the hatching success (64.25%), survival (46.71%), and heart rates (31.99%) of recently hatched larvae, being generally further exacerbated when warming and acidification co-occurred. On the other hand, acidification was the only factor to induce a significant decrease in the proportion of phototactic behaviour (50%). The behavioural and physiological responses showed to be highly correlated across experimental treatments, specifically, phototaxis was negatively correlated with the incidence of malformations, and positively correlated with heart rates. Overall, our findings indicate that the interaction between warming, acidification, and deoxygenation is markedly detrimental to fish early developmental stages, impacting several key features at this critical life stage that may eventually cause adverse carry-over effects. Importantly, our analysis highlights the need to assess the concurrent impacts of stressors’ interaction on marine taxa to better predict future ecosystem responses to ocean changes.

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Sponge organic matter recycling: reduced detritus production under extreme environmental conditions

Published 14 April 2023 Science Closed
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Highlights

  • Sponge metabolism was measured at the natural laboratory of Bouraké where sponges are naturally exposed to extreme conditions associated with tidal phase.
  • The photosymbiotic HMA sponge Rhabdastrella globostellata was able to cope with extreme acidification and deoxygenation seawater.
  • Photosynthetic activity of sponge symbionts was negatively affected during extreme environmental conditions.
  • The sponge loop pathway was disrupted during low tide, which correlated with extreme acidification, deoxygenation and warming seawater.

Abstract

Sponges are a key component of coral reef ecosystems and play an important role in carbon and nutrient cycles. Many sponges are known to consume dissolved organic carbon and transform this into detritus, which moves through detrital food chains and eventually to higher trophic levels via what is known as the sponge loop. Despite the importance of this loop, little is known about how these cycles will be impacted by future environmental conditions. During two years (2018 and 2020), we measured the organic carbon, nutrient recycling, and photosynthetic activity of the massive HMA, photosymbiotic sponge Rhabdastrella globostellata at the natural laboratory of Bouraké in New Caledonia, where the physical and chemical composition of seawater regularly change according to the tide. We found that while sponges experienced acidification and low dissolved oxygen at low tide in both sampling years, a change in organic carbon recycling whereby sponges stopped producing detritus (i.e., the sponge loop) was only found when sponges also experienced higher temperature in 2020. Our findings provide new insights into how important trophic pathways may be affected by changing ocean conditions.

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Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2

Published 12 April 2023 Science Closed
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Effects of changed levels of dissolved O2 and CO2 on marine primary producers are of general concern with respect to ecological effects of ongoing ocean deoxygenation and acidification as well as upwelled seawaters. We investigated the response of the diazotroph Trichodesmium erythraeum IMS 101 after it had acclimated to lowered pO2 (~60 μM O2) and/or elevated pCO2 levels (HC, ~32 μM CO2) for about 20 generations. Our results showed that reduced O2 levels decreased dark respiration significantly, and increased the net photosynthetic rate by 66 and 89% under the ambient (AC, ~13 μM CO2) and the HC, respectively. The reduced pO2 enhanced the N2 fixation rate by ~139% under AC and only by 44% under HC, respectively. The N2 fixation quotient, the ratio of N2 fixed per O2 evolved, increased by 143% when pO2 decreased by 75% under the elevated pCO2. Meanwhile, particulate organic carbon and nitrogen quota increased simultaneously under reduced O2 levels, regardless of the pCO2 treatments. Nevertheless, changed levels of O2 and CO2 did not bring about significant changes in the specific growth rate of the diazotroph. Such inconsistency was attributed to the daytime positive and nighttime negative effects of both lowered pO2 and elevated pCO2 on the energy supply for growth. Our results suggest that Trichodesmium decrease its dark respiration by 5% and increase its N2-fixation by 49% and N2-fixation quotient by 30% under future ocean deoxygenation and acidification with 16% decline of pO2 and 138% rise of pCO2 by the end of this century.

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Marked recent declines in boron in Baltic Sea cod otoliths – a bellwether of incipient acidification in a vast hypoxic system?

Published 11 April 2023 Science Closed
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Ocean acidification is spreading globally as a result of anthropogenic CO2 emissions, but the Baltic Sea has until recently been thought to be relatively well-buffered by terrigenous inputs of alkalinity from its watershed. We discovered a 3- to 5-fold decline in boron (as B : Ca) in otoliths of eastern Baltic Sea cod (EBC) between the late 1990s and 2021. B : Ca is positively proportional to pH in carbonates, as B in the form of borate is taken up in the CaCO3 matrix. Examining a time series of EBC otoliths, we found varying levels of B : Ca since the 1980s, with the most recent years at an all-time low during this period. This trend correlates with declines in pH and dissolved oxygen, but not with changes in salinity. We examined possible physiological influences on B : Ca by including a collection of healthy Icelandic cod as an out-group. Icelandic cod otoliths showed strongly positive correlations of B : Ca with physiologically regulated P : Ca; this was not the case for EBC. Finally, B : Ca in EBC otoliths is anti-correlated to some extent with Mn : Mg, a proposed proxy for hypoxia exposure. This negative relationship is hypothesized to reflect the dual phenomena of hypoxia and acidification as a result of decomposition of large algal blooms. Taken together, the otolith biomarkers Mn : Mg and B : Ca suggest a general increase in both hypoxia and acidification within the Baltic intermediate and deep waters in the last decade reflected in cod otoliths.

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Hypoxia tolerance, but not low pH tolerance, is associated with a latitudinal cline across populations of Tigriopus californicus

Published 6 April 2023 Science Closed
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Intertidal organisms must tolerate daily fluctuations in environmental parameters, and repeated exposure to co-occurring conditions may result in tolerance to multiple stressors correlating. The intertidal copepod Tigriopus californicus experiences diurnal variation in dissolved oxygen levels and pH as the opposing processes of photosynthesis and cellular respiration lead to coordinated highs during the day and lows at night. While environmental parameters with overlapping spatial gradients frequently result in correlated traits, less attention has been given to exploring temporally correlated stressors. We investigated whether hypoxia tolerance correlates with low pH tolerance by separately testing the hypoxia and low pH stress tolerance separately of 6 genetically differentiated populations of T. californicus. We independently checked for similarities in tolerance for each of the two stressors by latitude, sex, size, and time since collection as predictors. We found that although hypoxia tolerance correlated with latitude, low pH tolerance did not, and no predictor was significant for both stressors. We concluded that temporally coordinated exposure to low pH and low oxygen did not result in populations developing equivalent tolerance for both. Although climate change alters several environmental variables simultaneously, organisms’ abilities to tolerate these changes may not be similarly coupled.

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Acclimatization in a changing environment: linking larval and juvenile performance in the quahog Mercenaria mercenaria

Published 30 March 2023 Science Closed
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Marine invertebrates in coastal communities are currently experiencing unprecedented, rapid environmental change. These symptoms of climate change and ocean acidification are projected to worsen faster than can be accommodated by evolutionary processes like adaptation via natural selection, necessitating investigations of alternative mechanisms that facilitate adaptive responses to environmental change. This dissertation posits that in the absence of adaptation, early development (larval) exposure to stressors can increase population tolerance by leveraging existing variation in the energy metabolism and host-microbial interactions. Focusing specifically on resiliency to acidification (low pH), hypoxia (low dissolved oxygen), and elevated temperature stress in the clam, Mercenaria mercenaria, this dissertation uses a combination of laboratory and field experiments in conjunction with next-generation sequencing and physiological assays to investigate the relationship between host health, microbial community structure, and environmental change.

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The evolution of coral reef under changing climate: a scientometric review

Published 30 March 2023 Science Closed
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Simple Summary

Coral reefs are vital ecosystems with high biodiversity and ecological services for coastal communities. Climate change is accelerating, with detrimental consequences on coral reefs and related communities, but it is challenging to keep up with the literature given its current rapid expansion. The current review foresees three future trends in the area of coral reefs and climate change, including (i) incorporating future scenarios, (ii) climate-induced temperature changes, and (iii) adaptation strategies, which are expected to move society closer to the following Sustainable Development Goal: 13 Climate Action.

Abstract

In this scientometric review, we employ the Web of Science Core Collection to assess current publications and research trends regarding coral reefs in relation to climate change. Thirty-seven keywords for climate change and seven keywords for coral reefs were used in the analysis of 7743 articles on coral reefs and climate change. The field entered an accelerated uptrend phase in 2016, and it is anticipated that this phase will last for the next 5 to 10 years of research publication and citation. The United States and Australia have produced the greatest number of publications in this field. A cluster (i.e., focused issue) analysis showed that coral bleaching dominated the literature from 2000 to 2010, ocean acidification from 2010 to 2020, and sea-level rise, as well as the central Red Sea (Africa/Asia), in 2021. Three different types of keywords appear in the analysis based on which are the (i) most recent (2021), (ii) most influential (highly cited), and (iii) mostly used (frequently used keywords in the article) in the field. The Great Barrier Reef, which is found in the waters of Australia, is thought to be the subject of current coral reef and climate change research. Interestingly, climate-induced temperature changes in “ocean warming” and “sea surface temperature” are the most recent significant and dominant keywords in the coral reef and climate change area.

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The clam before the storm: a meta analysis showing the effect of combined climate change stressors on bivalves

Published 28 March 2023 Science Closed
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Impacts of a range of climate change on marine organisms have been analysed in laboratory and experimental studies. The use of different taxonomic groupings, and assessment of different processes, though, makes identifying overall trends challenging, and may mask phylogenetically different responses. Bivalve molluscs are an ecologically and economically important data-rich clade, allowing for assessment of individual vulnerability and across developmental stages. We use meta-analysis of 203 unique experimental setups to examine how bivalve growth rates respond to increased water temperature, acidity, deoxygenation, changes to salinity, and combinations of these drivers. Results show that anthropogenic climate change will affect different families of bivalves disproportionally but almost unanimously negatively. Almost all drivers and their combinations have significant negative effects on growth. Combined deoxygenation, acidification, and temperature shows the largest negative effect size. Eggs/larval bivalves are more vulnerable overall than either juveniles or adults. Infaunal taxa, including Tellinidae and Veneridae, appear more resistant to warming and oxygen reduction than epifaunal or free-swimming taxa but this assessment is based on a small number of datapoints. The current focus of experimental set-ups on commercially important taxa and families within a small range of habitats creates gaps in understanding of global impacts on these economically important foundation organisms.

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Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean

Published 24 March 2023 Science Closed
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Climate change impacts on fishery resources have been widely reported worldwide. Nevertheless, a knowledge gap remains for the warm-temperate Southwest Atlantic Ocean—a global warming hotspot that sustains important industrial and small-scale fisheries. By combining a trait-based framework and long-term landing records, we assessed species’ sensitivity to climate change and potential changes in the distribution of important fishery resources (n = 28; i.e., bony fishes, chondrichthyans, crustaceans, and mollusks) in Southern Brazil, Uruguay, and the northern shelf of Argentina. Most species showed moderate or high sensitivity, with mollusks (e.g., sedentary bivalves and snails) being the group with the highest sensitivity, followed by chondrichthyans. Bony fishes showed low and moderate sensitivities, while crustacean sensitivities were species-specific. The stock and/or conservation status overall contributed the most to higher sensitivity. Between 1989 and 2019, species with low and moderate sensitivity dominated regional landings, regardless of the jurisdiction analyzed. A considerable fraction of these landings consisted of species scoring high or very high on an indicator for potential to change their current distribution. These results suggest that although the bulk of past landings were from relatively climate-resilient species, future catches and even entire benthic fisheries may be jeopardized because (1) some exploited species showed high or very high sensitivities and (2) the increase in the relative representation of landings in species whose distribution may change. This paper provides novel results and insights relevant for fisheries management from a region where the effects of climate change have been overlooked, and which lacks a coordinated governance system for climate-resilient fisheries.

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Aquatic productivity under multiple stressors

Published 13 March 2023 Science Closed
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Aquatic ecosystems are responsible for about 50% of global productivity. They mitigate climate change by taking up a substantial fraction of anthropogenically emitted CO2 and sink part of it into the deep ocean. Productivity is controlled by a number of environmental factors, such as water temperature, ocean acidification, nutrient availability, deoxygenation and exposure to solar UV radiation. Recent studies have revealed that these factors may interact to yield additive, synergistic or antagonistic effects. While ocean warming and deoxygenation are supposed to affect mitochondrial respiration oppositely, they can act synergistically to influence the migration of plankton and N2-fixation of diazotrophs. Ocean acidification, along with elevated pCO2, exhibits controversial effects on marine primary producers, resulting in negative impacts under high light and limited availability of nutrients. However, the acidic stress has been shown to exacerbate viral attacks on microalgae and to act synergistically with UV radiation to reduce the calcification of algal calcifiers. Elevated pCO2 in surface oceans is known to downregulate the CCMs (CO2 concentrating mechanisms) of phytoplankton, but deoxygenation is proposed to enhance CCMs by suppressing photorespiration. While most of the studies on climate-change drivers have been carried out under controlled conditions, field observations over long periods of time have been scarce. Mechanistic responses of phytoplankton to multiple drivers have been little documented due to the logistic difficulties to manipulate numerous replications for different treatments representative of the drivers. Nevertheless, future studies are expected to explore responses and involved mechanisms to multiple drivers in different regions, considering that regional chemical and physical environmental forcings modulate the effects of ocean global climate changes.

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Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors

Published 2 March 2023 Science Closed
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Common sea stars (Asterias rubens) are at risk of physiological stress and decline with projected shifts in oceanic conditions. This study assessed changes in coelomic fluid (CF) blood gases, electrolytes, osmolality, and coelomocyte counts in adult common sea stars after exposure to stressors mimicking effects from climate change for 14 days, including decreased pH (−0.4 units, mean: 7.37), hypoxia (target dissolved oxygen ~1.75 mg O2/L, mean: 1.80 mg O2/L), or increased temperature (+10 °C, mean: 17.2 °C) and compared sea star CF electrolytes and osmolality to tank water. Changes in CF blood gases, electrolytes, and/or coelomocyte counts occurred in all treatment groups after stressor exposures, indicating adverse systemic effects with evidence of increased energy expenditure, respiratory or metabolic derangements, and immunosuppression or inflammation. At baseline, CF potassium and osmolality of all groups combined were significantly higher than tank water, and, after exposures, CF potassium was significantly higher in the hypoxia group as compared to tank water. These findings indicate physiological challenges for A. rubens after stressor exposures and, given increased observations of sea star wasting events globally, this provides evidence that sea stars as a broad group are particularly vulnerable to changing oceans.

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Life-stage-dependent effects of multiple flood-associated stressors on a coastal foundational species

Published 15 February 2023 Science Closed
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Global changes in precipitation patterns have increased the frequency and duration of flooding events. Freshwater inflows into estuaries reduce salinity levels and increase nutrient inputs, which can lead to eutrophication and impaired water quality. Oysters are important ecosystem engineers in coastal environments that are vulnerable to co-occurring environmental stressors associated with freshwater flooding events. Successful recruitment is necessary to maintain adult oyster populations, but early life stage responses to multiple stressors are not well understood. Flood-associated stressor conditions were observed near oyster habitats at multiple locations across the northern Gulf of Mexico during peak recruitment months in the spring and summer of 2021. In the laboratory, we examined the interactive effects of acidification, hypoxia, and low salinity on larval and juvenile life stages of the eastern oyster (Crassostrea virginica) to better understand the impact of flooding events on oyster development and survival. Salinity stress in isolation reduced larval growth and settlement, and decreased survival and growth at the juvenile stage. Hypoxia was more stressful to oyster larvae than to juveniles, whereas low pH had negative effects on juvenile growth. There were no synergistic effects of multiple flood-associated stressors on early oyster life stages and effects were either additive or predicted by the salinity stress response. The negative impacts of flooding disturbances on recruitment processes in benthic populations need to be considered in restoration planning and flood control mitigation strategies as the frequency and intensity of extreme freshwater events continue to rise worldwide.

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Physiological and gene expression responses of the mussel Mytilus galloprovincialis to low pH and low dissolved oxygen

Published 10 February 2023 Science Closed
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Graphical abstract.

Highlight

  • Low pH and DO, alone or in combination, affected physiology and gene expression in mussels.
  • Low pH alone led to a decrease of all tested physiological parameters.
  • Low DO decreased the clearance rate, modulated haemocytes parameters, increased carbohydrates levels.
  • The combined effect of low pH and low DO could not be predicted by a simple arithmetic additive response.

Abstract

The prevalence and frequency of hypoxia events have increased worldwide over the past decade as a consequence of global climate change and coastal biological oxygen depletions. On the other hand, anthropogenic emissions of CO2 and consequent accumulation in the sea surface result in a perturbation of the seawater carbonate system, including a decrease in pH, known as ocean acidification. While the effect of decreases in pH and dissolved oxygen (DO) concentration is better understood, their combined effects are still poorly resolved. Here, we exposed adult mussels (Mytilus galloprovincialis) to two pHs (8.27 and 7.63) and DO concentrations (7.65 and 2.75 mg L−1) over 17 days in a full-factorial design. These levels correspond to extremes of the present natural variability and are relevant in the context of ocean acidification and hypoxia. No mortality was observed during the experiment. However, sublethal effects were observed for clearance and oxygen consumption rates, as well as total haemocytes count and haemocytes viability and gene expression in mussels exposed to the combination of low pH and low DO. Respiration and excretion rates were not significantly impacted by low pH and DO, alone or in combination. Overall, low pH alone led to a decrease in all tested physiological parameters while low DO alone led to a decline in clearance rate, haemocyte parameters and an increase in carbohydrate content. Both parameters led to up- or down-regulation of most of the selected genes. Not surprisingly, the combined effect of low pH and low DO could not be predicted by a simple arithmetic additive response at the effect level, highlighting more complex and non-linear effects.

Continue reading ‘Physiological and gene expression responses of the mussel Mytilus galloprovincialis to low pH and low dissolved oxygen’

Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors

Published 8 February 2023 Science Closed
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Common sea stars (Asterias rubens) are at risk of physiological stress and decline with projected shifts in oceanic conditions. This study assessed changes in coelomic fluid (CF) blood gases, electrolytes, osmolality, and coelomocyte counts in adult common sea stars after exposure to stressors mimicking effects from climate change for 14 days, including decreased pH (−0.4 units, mean: 7.37), hypoxia (target dissolved oxygen ~1.75 mg O2/L, mean: 1.80 mg O2/L), or increased temperature (+10 °C, mean: 17.2 °C) and compared sea star CF electrolytes and osmolality to tank water. Changes in CF blood gases, electrolytes, and/or coelomocyte counts occurred in all treatment groups after stressor exposures, indicating adverse systemic effects with evidence of increased energy expenditure, respiratory or metabolic derangements, and immunosuppression or inflammation. At baseline, CF potassium and osmolality of all groups combined were significantly higher than tank water, and, after exposures, CF potassium was significantly higher in the hypoxia group as compared to tank water. These findings indicate physiological challenges for A. rubens after stressor exposures and, given increased observations of sea star wasting events globally, this provides evidence that sea stars as a broad group are particularly vulnerable to changing oceans.

Continue reading ‘Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors’

Population-specific vulnerability to ocean change in a multistressor environment

Published 26 January 2023 Science Closed
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Variation in environmental conditions across a species’ range can alter their responses to environmental change through local adaptation and acclimation. Evolutionary responses, however, may be challenged in ecosystems with tightly coupled environmental conditions, where changes in the covariance of environmental factors may make it more difficult for species to adapt to global change. Here, we conduct a 3-month-long mesocosm experiment and find evidence for local adaptation/acclimation in populations of red sea urchins, Mesocentrotus franciscanus, to multiple environmental drivers. Moreover, populations differ in their response to projected concurrent changes in pH, temperature, and dissolved oxygen. Our results highlight the potential for local adaptation/acclimation to multivariate environmental regimes but suggest that thresholds in responses to a single environmental variable, such as temperature, may be more important than changes to environmental covariance. Therefore, identifying physiological thresholds in key environmental drivers may be particularly useful for preserving biodiversity and ecosystem functioning.

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Metabolic adaptation of fishes under different consequences of climate change

Published 26 January 2023 Science Closed
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Aquaculture sustainability is affected by climate change which regulated livelihood, nutrition and world food security. The most important contributor to climate change is documented by a human due to deforestation and industries that release GHGs (greenhouse gases) accumulated in the surrounding environment such as methane, nitrous oxide, fluorinated gases and carbon dioxide. Climate change affected fisheries adversely but it is overshadowing the positive one. The effects of climate change on fishes can be directed by water quality parameters such as temperature, dissolve oxygen, pH (acidification) etc. which affected fish physiology and behavioural changes through metabolic adaptation. Due to the changes in climate fishes are adapting to a novel environment like high temperatures (higher to lower latitude or lower to higher latitude), a hypoxic condition due to evolutionary effect and adapting to low pH which is caused by high carbon dioxide released in the environment by human activities. This chapter mainly focuses on how fishes are adapting to the novel climatic condition such as a high or low temperature, hypoxic conditions and low pH through the metabolic activity through enzymatic action (fish physiology) and morphological changes like gill structure to cope with low oxygen and acidification of natural water body.

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Invited review – the effects of anthropogenic abiotic stressors on the sensory systems of fishes

Published 25 January 2023 Science Closed
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Graphical abstract.

Highlights

  • Conditions in abiotic factors of oceans and freshwater habitats are changing quickly due to anthropogenic activity.
  • Low pH impairs olfaction and vision, alters otolith growth, and affects CNS functioning.
  • High temperatures increase the signalling speed of nerves, alters sensory processing, and increases ROS in the CNS.
  • Low oxygen impairs energy production, nerve conduction speed, negatively affects vision and causes apoptosis in the brain.

Abstract

Climate change is a growing global issue with many countries and institutions declaring a climate state of emergency. Excess CO2 from anthropogenic sources and changes in land use practices are contributing to many detrimental changes, including increased global temperatures, ocean acidification and hypoxic zones along coastal habitats. All senses are important for aquatic animals, as it is how they can perceive and respond to their environment. Some of these environmental challenges have been shown to impair their sensory systems, including the olfactory, visual, and auditory systems. While most of the research is focused on how ocean acidification affects olfaction, there is also evidence that it negatively affects vision and hearing. The effects that temperature and hypoxia have on the senses have also been investigated, but to a much lesser extent in comparison to ocean acidification. This review assembles the known information on how these anthropogenic challenges affect the sensory systems of fishes, but also highlights what gaps in knowledge remain with suggestions for immediate action.

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Evaluation of the current understanding of the impact of climate change on coral physiology after three decades of experimental research

Published 24 January 2023 Science Closed
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After three decades of coral research on the impacts of climate change, there is a wide consensus on the adverse effects of heat-stress, but the impacts of ocean acidification (OA) are not well established. Using a review of published studies and an experimental analysis, we confirm the large species-specific component of the OA response, which predicts moderate impacts on coral physiology and pigmentation by 2100 (scenario-B1 or SSP2-4.5), in contrast with the severe disturbances induced by only +2 °C of thermal anomaly. Accordingly, global warming represents a greater threat for coral calcification than OA. The incomplete understanding of the moderate OA response relies on insufficient attention to key regulatory processes of these symbioses, particularly the metabolic dependence of coral calcification on algal photosynthesis and host respiration. Our capacity to predict the future of coral reefs depends on a correct identification of the main targets and/or processes impacted by climate change stressors.

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Multistressor global change drivers reduce hatch and viability of Lingcod embryos, a benthic egg layer in the California Current System

Published 10 January 2023 Science Closed
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Early life history stages of marine fishes are often more susceptible to environmental stressors than adult stages. This vulnerability is likely exacerbated for species that lay benthic egg masses bound to substrate because the embryos cannot evade locally unfavorable environmental conditions. Lingcod (Ophiodon elongatus), a benthic egg layer, is an ecologically and economically significant predator in the highly-productive California Current System (CCS). We ran a flow-through mesocosm experiment that exposed Lingcod eggs collected from Monterey Bay, CA to conditions we expect to see in the central CCS by the year 2050 and 2100. Exposure to temperature, pH, and dissolved oxygen concentrations projected by the year 2050 halved the successful hatch of Lingcod embryos and significantly reduced the size of day-1 larvae. In the year 2100 treatment, viable hatch plummeted (3% of normal), larvae were undersized (83% of normal), yolk reserves were exhausted (38% of normal), and deformities were widespread (94% of individuals). This experiment is the first to expose marine benthic eggs to future temperature, pH, and dissolved oxygen conditions in concert. Lingcod are a potential indicator species for other benthic egg layers for which global change conditions may significantly diminish recruitment rates.

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