Posts Tagged 'fish'

Impact of ocean warming and acidification on the behaviour of two co-occurring gadid species, Boreogadus saida and Gadus morhua, from Svalbard

Ocean acidification induces strong behavioural alterations in marine fish as a consequence of acid-base regulatory processes in response to increasing environmental CO2 partial pressure. While these changes have been investigated in tropical and temperate fish species, nothing is known about behavioural effects on polar species. In particular, fishes of the Arctic Ocean will experience much greater acidification and warming than temperate or tropical species. Also, possible interactions of ocean warming and acidification are still understudied. Here we analysed the combined effects of warming and acidification on behavioural patterns of 2 fish species co-occurring around Svalbard, viz. polar cod Boreogadus saida and Atlantic cod Gadus morhua. We found a significant temperature effect on the spontaneous activity of B. saida, but not of G. morhua. Environmental CO2 did not significantly influence activity of either species. In contrast, behavioural laterality of B. saida was affected by CO2 but not by temperature. Behavioural laterality of G. morhua was not affected by temperature or CO2; however, in this species, a possible temperature dependency of CO2 effects on relative laterality may have been missed due to sample size restrictions. This study indicates that fish in polar ecosystems may undergo some, albeit less intense, behavioural disturbances under ocean acidification and in combination with ocean warming than observed in tropical species. It further accentuates species-specific differences in vulnerability.

Continue reading ‘Impact of ocean warming and acidification on the behaviour of two co-occurring gadid species, Boreogadus saida and Gadus morhua, from Svalbard’

Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival

Diel fluctuations in dissolved oxygen (DO) and pH create hypoxic conditions that alter the quality of shallow estuarine nursery habitats for juvenile fishes. Understanding how different species in these environments mitigate stress associated with intermittent hypoxia through compensatory behaviors, such as aquatic surface respiration (ASR), is important in determining the effect of these stressors on estuarine ecosystems. Behavioral responses of Atlantic silversides (Menidia menidia), striped killifish (Fundulus majalis), mummichog (Fundulus heteroclitus), and juvenile striped bass (Morone saxatilis) were independently observed during exposure to two levels of diel-cycling DO (3–9 mg O2 l− 1 and 1–11 mg O2 l− 1) each tested with both the corresponding pH cycle (7.2–7.8 and 6.8–8.1, respectively) and static pH (7.5) under controlled laboratory conditions. In treatments in which DO declined to ~ 3 mg O2 l− 1, none of the species examined exhibited ASR behavior either with or without the associated pH decline. However, ASR was observed during both 4-hour and extended 16-hour exposure where DO declined to ~ 1.0–1.6 mg O2 l− 1 in M. menidia and both Fundulus species. M. saxatilis did not exhibit ASR and no mortalities occurred during 4-hour low DO/pH treatments or during 16 hour exposure to 1.5 mg O2 l− 1. During extended 16-hour treatments, DO thresholds for ASR were not found to be different between F. majalis and F. heteroclitus, but both differed significantly from M. menidia. Across both 4-hour and 16-hour treatments, the onset of ASR was observed in M. menidia at or near lethal levels (1.31–1.62 mg O2 l− 1). No evidence of a pH (pCO2) effect on ASR or survival was found in any species in response to naturally co-varying DO and pH swings, despite pH as low as 6.8 and high pCO2 levels of >~12,000 μatm. These results suggest that utilization of ASR is a species-specific response influenced by the magnitude and duration of hypoxic exposure. ASR may serve as a last-ditch strategy by M. menidia to prolong survival for minutes to hours, but function as a means for F. heteroclitus to mitigate or reduce negative effects of hypoxia on a scale of days to weeks, with F. majalis exhibiting an intermediate response.

Continue reading ‘Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival’

Ocean acidification dampens warming and contamination effects on the physiological stress response of a commercially important fish

Increases in carbon dioxide (CO2) and other greenhouse gases emissions are leading to changes in ocean temperature and carbonate chemistry, the so-called ocean warming and acidification phenomena, respectively. Methylmercury (MeHg) is the most abundant form of mercury (Hg), well-known for its toxic effects on biota and environmental persistency. Despite more than likely co-occurrence in future oceans, the interactive effects of these stressors are largely unknown. Here we assessed organ-dependent Hg accumulation (gills, liver and muscle) within a warming (ΔT = 4 ºC) and acidification (ΔpCO2 = 1100 µatm) context, and the respective phenotypic responses of molecular chaperone and antioxidant enzymatic machineries, in a commercially important fish (the meagre Argyrosomus regius). After 30 days of exposure, although no mortalities were observed in any treatments, Hg concentration was significantly enhanced under warming conditions, significantly more so in the liver. On the other hand, increased CO2 decreased Hg accumulation and, despite negative effects prompted as a sole stressor, consistently elicited an antagonistic effect with temperature and contamination on oxidative stress (catalase, superoxide dismutase and glutathione-S-tranferase activities) and heat shock (Hsp70 levels) responses. We argue that the mechanistic interactions are grounded on simultaneous increase in excessive hydrogen (H+) and reactive oxygen species (e.g. O2−) free radicals, and subsequent chemical reaction equilibrium balancing. Additional multi-stressor experiments are needed to understand such biochemical mechanism and further disentangle interactive (additive, synergistic or antagonistic) stressor effects on fish ecophysiology in the oceans of tomorrow.

Continue reading ‘Ocean acidification dampens warming and contamination effects on the physiological stress response of a commercially important fish’

Structural and functional organization of fish assemblages in a Mediterranean shallow CO2 vent

The “business-as-usual emission scenario” simulated by the IPCC (Intergovernmental Panel on Climate Change) suggests that atmospheric CO2 levels could approach 800 ppm by the end of the century. Corresponding biogeochemical models indicate that surface ocean water pH will drop from a pre-industrial value of about 8.2 to 7.8 within 2100 (Feely et al., 2010). This phenomenon known as “Ocean Acidification” (OA) is caused by the increasing CO2 emissions due to anthropic activities, with a current consequence decrease of about 0.1 unit of pH (Caldeira & Wickett 2003) that is having effects on seawater carbonate chemistry and on marine ecosystems. Many short-term laboratory experiments have shown the effects of OA on marine calcareous organisms (Doney et al., 2009), but also on not-calcifying ones. For instance, experiments on fish have revealed effects on physiological and behavioral aspects (Dixson et al., 2010; Munday et al., 2009), but many other aspects are still unknown (Ishimatsu et al., 2008). On the other hand, field experiments have been conducted in naturally acidified marine ecosystems, known as CO2 vents, which are currently investigated to study the long-term effects of OA on species, communities and ecological processes (Hall-Spencer et al. 2008).

Shallow CO₂ vents are widespread in Mediterranean (Dando et al., 1999) and represent a sort of natural mesocosms, where marked pH gradients are present at small spatial scales. The aim of this PhD project is to assess the effect of high pCO2/low pH on the structural and functional organization of fish assemblages in a Mediterranean shallow CO₂ vent (Aeolian Archipelago, NE Sicily). In particular, we compare the responses of a chronic exposed fish assemblage living near the primary vent (mean pH = 7.8; hereafter “Low pH”) with other two fish assemblages living at normal pH (mean pH = 8.2; hereafter “Control 1” and “Control 2”) in Vulcano and Lipari Islands. We hypothesized that the organization of fish assemblage at the low pH site is different from that in controls. To test our hypothesis we use several descriptors and different methodologies. First, we compared fish community structure by using Underwater Visual Census technique to assess species richness and abundance (frequency of occurrence). Then we carried out samplings to evaluate trophic organization of fish assemblages (we used stable isotopes of carbon and nitrogen to analyze food web and trophic levels), bioaccumulation and biomagnification of trace elements (concentration and bio-availability of several trace elements, also toxic ones, may increase due to direct input from the vent and to peculiar pH and Eh conditions), and the characteristics of carbonate structures like otoliths (to assess the effect of acidification on these structures by morphological analysis). Otoliths are also used as natural tags to study fish “site fidelity” of this particular site through microchemistry analysis of trace elements and isotopic composition.

This study provided a complete and exhaustive frame of fish assemblages structure and trophic organization at different pH levels. As scant data are available in the literature on this topic, the results of this research provide information about the ecological effects of long-term exposure to high CO2 levels on fish, a key biological component whose monitoring is relevant not only from the ecological side, but also for the economic one and for the implications on human health. Moreover, this study confirms the importance to use the naturally acidified environments to test ecological hypotheses on the effects of OA on communities and ecosystems.

Continue reading ‘Structural and functional organization of fish assemblages in a Mediterranean shallow CO2 vent’

Boosted food web productivity through ocean acidification collapses under warming

Future climate is forecast to drive bottom-up (resource driven) and top-down (consumer driven) change to food web dynamics and community structure. Yet, our predictive understanding of these changes is hampered by an over-reliance on simplified laboratory systems centred on single trophic levels. Using a large mesocosm experiment, we reveal how future ocean acidification and warming modify trophic linkages across a three-level food web: that is, primary (algae), secondary (herbivorous invertebrates) and tertiary (predatory fish) producers. Both elevated CO2 and elevated temperature boosted primary production. Under elevated CO2, the enhanced bottom-up forcing propagated through all trophic levels. Elevated temperature, however, negated the benefits of elevated CO2 by stalling secondary production. This imbalance caused secondary producer populations to decline as elevated temperature drove predators to consume their prey more rapidly in the face of higher metabolic demand. Our findings demonstrate how anthropogenic CO2 can function as a resource that boosts productivity throughout food webs, and how warming can reverse this effect by acting as a stressor to trophic interactions. Understanding the shifting balance between the propagation of resource enrichment and its consumption across trophic levels provides a predictive understanding of future dynamics of stability and collapse in food webs and fisheries production.

Continue reading ‘Boosted food web productivity through ocean acidification collapses under warming’

Effects of elevated CO₂ on speckled sanddab (Citharichthys stigmaeus) behaviour

The direct and indirect effects of ocean acidification (OA) are a growing concern, particularly in areas already experiencing elevated levels of oceanic CO₂. Studies with marine fishes suggest that elevated CO₂ levels may affect behavior by interfering with an important brain neurotransmitter. Studies examining the effects of OA fish behavior have been predominately conducted on tropical fishes; few have been conducted on fishes from temperate and boreal regions. The productive ecosystems of these regions, such as those of the California Current, support important commercial fisheries. Parts of the California Current are already experiencing elevated CO₂ during seasonal upwelling events. Flatfishes are an important component of the ecosystems of the California Current; not only do flatfishes support important regional fisheries, but they also are an important link in energy transfer within marine food webs. To date there has been little work examining the effects of OA on flatfish behavior. In laboratory experiments, I first examined speckled sanddab (Citharichthys stigmaeus) behavioral responses to potential predation cues (predator odor, damaged skin cues from injured conspecifics, and sight of a predator) under ambient CO₂ conditions. Whereas sanddab exhibited reductions in conspicuousness and foraging following exposure to the sight of a predator, they increased activity and foraging following exposure to damaged skin cues from injured conspecifics. I then examined the effects of elevated CO₂ levels on posture, activity, and foraging of sanddab, and if CO₂ altered their responses to damaged skin cues. CO₂ treatments reflected present-day CO₂ levels (~ 400μatm) and those predicted to occur over the next 150 years (~1,000 μatm and ~1,600 μatm). While there was no major effect of CO₂ treatment on the behavior of speckled sanddab, there were non-significant trends of fish from the medium CO₂ treatment exhibiting the lowest posture and activity scores, longest feeding latencies, and fewest feeding strikes. Results suggest that aspects of speckled sanddab behavior might resistant to OA. It is also possible that prolonged exposure to elevated CO₂ enabled speckled sanddab to compensate, mitigating the effects observed in other fishes following shorter-term exposure to elevated CO₂. Experiments further examining the interactive effects of elevated CO₂ with other environmental conditions on speckled sanddab behavior can also provide insight into the potential ecological consequences of life in an ocean altered by global climate change. Additional studies of ecologically relevant behaviors across diverse species assemblages will be needed to evaluate the impact of ocean acidification on marine food webs.

Continue reading ‘Effects of elevated CO₂ on speckled sanddab (Citharichthys stigmaeus) behaviour’

Impacts of CO2-induced ocean acidification on predator detection ability and developementof temperate fish

Ocean acidification, caused by elevated levels of atmospheric carbon dioxide (CO2), is recognized as a serious threat to marine ecosystems. Until now, most studies have focused on marine calcifying organisms, due to dependence on calcium carbonate, which is likely to become limited under future acidification scenarios. Less attention has been given to fish, but recent studies on the early life stages suggest that behavior, growth, development and otolith size may be highly affected by increasing CO2 levels. Other studies, on the other hand, fail to detect negative effects, suggesting species-specific vulnerabilities to increasing concentrations of CO2 and point to a need of further research. Here we tested the effects of CO2-induced ocean acidification on the early life stages of a temperate marine fish, the clingfish Lepadogaster lepadogaster, by rearing larvae since hatching in control and high pCO2 conditions. Size-at-age metrics and otolith size were examined in pre-settlement stage larvae. Additionally, behavioral response to a predator odour was tested in L. lepadogaster larvae and in Atherina presbyter larvae, maintained in high pCO2 conditions. Recognition of predator odours is a key behavior for predator avoidance and survival, and is one of the most commonly affected behaviors in fishes exposed to high CO2 levels. Results suggest that early life stages of L. lepadogaster might be resilient to future scenarios of ocean acidification, whereas A. presbyter might be more susceptible, with potential impacts on its future survival. Future studies should address species capacity to adapt to the predicted ocean acidification over the next century.

Continue reading ‘Impacts of CO2-induced ocean acidification on predator detection ability and developementof temperate fish’


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