Posts Tagged 'Chordata'

Responses of a coral reef shark acutely exposed to ocean acidification conditions

Anthropogenic ocean acidification (OA) is a threat to coral reef fishes, but few studies have investigated responses of high-trophic-level predators, including sharks. We tested the effects of 72-hr exposure to OA-relevant elevated partial pressures of carbon dioxide (pCO2) on oxygen uptake rates, acid–base status, and haematology of newborn tropical blacktip reef sharks (Carcharhinus melanopterus). Acute exposure to end-of-century pCO2 levels resulted in elevated haematocrit (i.e. stress or compensation of oxygen uptake rates) and blood lactate concentrations (i.e. prolonged recovery) in the newborns. Conversely, whole blood and mean corpuscular haemoglobin concentrations, blood pH, estimates of standard and maximum metabolic rates, and aerobic scope remained unaffected. Taken together, newborn blacktip reef sharks appear physiologically robust to end-of-century pCO2 levels, but less so than other, previously investigated, tropical carpet sharks. Our results suggest peak fluctuating pCO2 levels in coral reef lagoons could still physiologically affect newborn reef sharks, but studies assessing the effects of long-term exposure and in combination with other anthropogenic stressors are needed.

Continue reading ‘Responses of a coral reef shark acutely exposed to ocean acidification conditions’

Energetic context determines species and community responses to ocean acidification

Physiological responses to ocean acidification are thought to be related to energetic trade‐offs. Although a number of studies have proposed that negative responses to low pH could be minimized in situations where food resources are more readily available, evidence for such effects on individuals remain mixed, and the consequences of such effects at the community level remain untested. We explored the potential for food availability and diet quality to modify the effects of acidification on developing marine fouling communities in field‐deployed mesocosms by supplementing natural food supply with one of two species of phytoplankton, differing in concentration of fatty acids. After twelve weeks, no species demonstrated the interactive effects generally predicted in the literature, where a positive overall effect of diet mitigated the negative overall effects of acidification. Rather, for some species, additional food supply appeared to bring out or exacerbate the negative effects of low pH. Community richness and structure were only altered by acidification, while space occupation and evenness reflected patterns of the most dominant species. Importantly, we find that acidification stress can increase the relative abundance of invasive species, even under resource conditions that otherwise prevented invasive species establishment. Overall, the proposed hypothesis regarding the ability for food addition to mitigate the negative effects of acidification is thus far not widely supported at species or community levels. It is clear that acidification is a strong driving force in these communities but understanding underlying energetic and competitive context is essential to developing mechanistic predictions for climate change responses.

Continue reading ‘Energetic context determines species and community responses to ocean acidification’

Effects of elevated carbon dioxide on the hematological parameters of a temperate catshark

Atmospheric CO2 levels have been rising due to an increase in anthropic activities and its implications over marine ecosystems are unprecedented. The present study focused on the effects of ocean acidification (OA) on key hematological parameters of the juvenile small‐spotted catsharks (Scyliorhinus canicula). Eggs were reared throughout the entire embryogenesis (~4 months) plus 5 additional months, in two experimental treatments (control: pCO2 ~ 400 μatm; and high CO2: pCO2 ~ 900 μatm, Δ −0.3 pH units). After blood collection, the following hematological parameters were evaluated: (a) normal blood cells count (erythrocytes, leukocytes, and thrombocytes), (b) presence of erythrocytes with nuclear abnormalities, and (c) erythrocyte nucleus to cytoplasmic ratio. Concomitantly, to determine the cardiac and hematopoietic conditions, the spleen and heart to body ratios were also assessed. The present findings indicate that the measured variables may not be affected by elevated pCO2 in this temperate species, as no significant differences were observed between treatments across all the endpoints tested. Nonetheless, it is worth mentioning a decreasing trend observed in a number of thrombocytes associated with OA, which should foster further investigation, regarding other aspects of their coagulation response. Along with OA, other stressors are expected to impact marine life, such as warming and hypoxia. Thus, future research should aim to investigate the cumulative effect of these stressors on hematological parameters in sharks.

Continue reading ‘Effects of elevated carbon dioxide on the hematological parameters of a temperate catshark’

Sperm motility impairment in free spawning invertebrates under near-future level of ocean acidification: uncovering the mechanism

Ocean acidification (OA) refers to the decrease in ocean water pH resulting from the increasing absorption of atmospheric CO2. This will cause changes in the ocean’s carbonate chemistry system with a resulting impact on reproduction of marine organisms. Reproduction is the fundamental process that allows the conservation of the species; in free-spawning marine invertebrates, this process is highly sensitive to changes in seawater quality and chemistry. To date, the majority of the studies concerned OA effects on reproduction has been focused on embryo and larval development. Despite several evidence for the impairment of reproductive success by environmental perturbations through altering gamete quality, sperm physiological responses to OA are poorly investigated. In this study, we evaluated the effects of exposure to acidified seawater (AcSW) (pH 7.8), which approximate the predicted global averages for oceanic surface waters at the end of this century, on sperm quality of the mussel Mytilus galloprovincialis and the ascidian Ciona robusta by evaluating several endpoints, such as motility, vitality, mitochondrial activity, oxidative state, and intracellular pH (pHi). Following sperm exposure to AcSW, the percentage of motile spermatozoa, mitochondrial activity and pHi decreased in comparison to the current seawater pH of 8.1, whereas vitality and oxidative state were unaffected by the low external pH in both the species. In broadcast spawners, a relationship between sperm intracellular pH and the initiation of motility are well known. Spermatozoa are immotile in the testes and motility is induced after the spermatozoa are released into seawater; the alkaline pH of seawater, in fact, increases the pHi activating motility and mitochondrial respiration. The results of this study suggest that the lowering of seawater pH as predicted to occur for 2100, through the inhibition of pHi increase, prevent sperm motility activation. Sperm motility is a key determinant of fertilization success; consequently, a corresponding drop in fertilization success would be expected with important implications for the fitness and the survival of marine invertebrates.

Continue reading ‘Sperm motility impairment in free spawning invertebrates under near-future level of ocean acidification: uncovering the mechanism’

Ocean acidification impact on ascidian Ciona robusta spermatozoa: new evidence for stress resilience

Highlights

• Impact of ocean acidification on sperm quality of the ascidian Ciona robusta was investigated.

• Two experimental approaches were set up to simulate the ocean conditions predicted for the end of this century.

• Alteration of sperm motility, morphology and physiology was detected in short-term exposure.

• A rapid recovery of physiological conditions was observed within one week.

• New evidence of resilience in ascidian C. robusta spermatozoa in response to ocean acidification.

Abstract

Rising atmospheric CO2 is causing a progressive decrease of seawater pH, termed ocean acidification. Predicting its impact on marine invertebrate reproduction is essential to anticipate the consequences of future climate change on species fitness and survival. Ocean acidification may affect reproductive success either in terms of gamete or progeny quality threating species survival. Despite an increasing number of studies focusing on the effects of ocean acidification on the early life history of marine organisms, very few have investigated the effects on invertebrate gamete quality. In this study, we set up two experimental approaches simulating the ocean conditions predicted for the end of this century, in situ transplant experiments at a naturally acidified volcanic vent area along the Ischia island coast and microcosm experiments, to evaluate the short-term effects of the predicted near-future levels of ocean acidification on sperm quality of the ascidian Ciona robusta after parental exposure. In the first days of exposure to acidified conditions, we detected alteration of sperm motility, morphology and physiology, followed by a rapid recovery of physiological conditions that provide a new evidence of resilience of ascidian spermatozoa in response to ocean acidification. Overall, the short-term tolerance to adverse conditions opens a new scenario on the marine species capacity to continue to reproduce and persist in changing oceans.

Continue reading ‘Ocean acidification impact on ascidian Ciona robusta spermatozoa: new evidence for stress resilience’

Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species

Predictions of the effects of global change on ecological communities are largely based on single habitats. Yet in nature, habitats are interconnected through the exchange of energy and organisms, and the responses of local communities may not extend to emerging community networks (i.e. metacommunities). Using large mesocosms and meiofauna communities as a model system, we investigated the interactive effects of ocean warming and acidification on the structure of marine metacommunities from three shallow‐water habitats: sandy soft‐bottoms, marine vegetation and rocky reef substrates. Primary producers and detritus – key food sources for meiofauna – increased in biomass under the combined effect of temperature and acidification. The enhanced bottom‐up forcing boosted nematode densities but impoverished the functional and trophic diversity of nematode metacommunities. The combined climate stressors further homogenized meiofauna communities across habitats. Under present‐day conditions metacommunities were structured by habitat type, but under future conditions they showed an unstructured random pattern with fast‐growing generalist species dominating the communities of all habitats. Homogenization was likely driven by local species extinctions, reducing interspecific competition that otherwise could have prevented single species from dominating multiple niches. Our findings reveal that climate change may simplify metacommunity structure and prompt biodiversity loss, which may affect the biological organization and resilience of marine communities.

Continue reading ‘Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species’

Early development and metabolic physiology of the temperate lesser spotted shark (Scyliorhinus canicula) under high CO2 levels

Although sharks thrive in many different kinds of habitats and evolved to fill many ecological niches across a wide range of habitats, these animals are characterized by the limited capability to adapt rapidly to future climate change. Thus, the objective of the present dissertation was to analyze the potential impact of seawater acidification (OA, high CO2 levels ~1000 μatm) on the early development and physiology of the temperate shark Scyliorhinus canicula. More specifically, we evaluated OA effects on: i) development time and first feed, ii) Fulton condition of the newborns, iii) survival, iv) routine metabolic rate (RMR), v) maximum metabolic rate (MMR), and vi) aerobic scope (AS). The duration of embrygenesis ranged from 118 to 125 days, and after hatching, the mean number of days to start feeding (i.e. first feeding) varied between 4 and 6 days. In both endpoints there were no significant differences among treatments (i.e. normocapnia and hypercapnia; p >0.05). Juvenile survival (after 150 days post-hatching) also did no change significantly under high CO2 levels (p >0.05). Regarding energy expenditure rates and aerobic window, there were no significant differences in RMR, MMR, and AS among treatments (p-value > 0.005). In the overall, we argue that these findings are associated to the fact that S. canicula is a benthic, cosmopolitan and temperate shark usually exposed to great variations of abiotic factors, like those experienced in the highly-dynamic western Portuguese coast (with seasonal upwelling events). Although the present dissertation only investigated acclimation processes, it is plausible to assume that this shark species will not be greatly affected by future acidification conditions.

Continue reading ‘Early development and metabolic physiology of the temperate lesser spotted shark (Scyliorhinus canicula) under high CO2 levels’

Impact of climate change and contamination in the oxidative stress response of marine organisms

Atmospheric carbon dioxide (CO2) levels are increasing at an unprecedented rate, changing the carbonate chemistry (in a process known as ocean acidification) and temperature of the worlds ocean. Moreover, the simultaneous occurrence of highly toxic and persistent contaminants, such as mercury, will play a key role in further shaping the ecophysiology of marine organisms. Thus, the main goal of the present dissertation was to undertake the first comprehensive and comparative analysis of the biochemical strategies, namely antioxidant defense (both enzymatic and non-enzymatic antioxidants) and protein repair and removal mechanisms, of several marine organisms – from invertebrate (Veretillum cynomorium and Gammarus locusta) to vertebrate species (Argyrosomus regius, Chiloscyllium plagiosum and Scyliorhinus canicula) – encompassing different life-stages and life-strategies to the predicted climate-mediated changes. The findings provided in the present dissertation proved that organisms’ responses were mostly underpinned by temperature (increasing lipid, protein and nucleic acid damage), that also culminated into increased mercury bioaccumulation and toxicity, while ocean acidification as a sole stressor usually played a minor role in defining species vulnerability (i.e. responsible for increased oxidative damage in the marine calcifying organisms G. locusta). Nonetheless when co-occurring with warming and contamination scenarios, acidification was usually responsible for the reduction of heavy metal accumulation and toxicity, as well as decreased warming and contamination-elicited oxidative stress. Additionally, organisms’ responses were species-specific, and organisms that usually occupy more variable environments (e.g. daily changes in abiotic conditions) usually displayed greater responses towards environmental change than organisms inhabiting more stable environments. Furthermore, and assuming the relevance of transgenerational effects, it seems that the negative effects of OA are potentially being inherited by the offspring’s, compromising the efficiency of future generations to endure the upcoming conditions.

Continue reading ‘Impact of climate change and contamination in the oxidative stress response of marine organisms’

Ocean warming and acidification may challenge the riverward migration of glass eels

The dramatic decline of European eel (Anguilla anguilla) populations over recent decades has attracted considerable attention and concern. Furthermore, little is known about the sensitivity of the early stages of eels to projected future environmental change. Here, we investigated, for the first time, the potential combined effects of ocean warming (OW; Δ + 4°C; 18°C) and acidification (OA; Δ − 0.4 pH units) on the survival and migratory behaviour of A. anguilla glass eels, namely their preference towards riverine cues (freshwater and geosmin). Recently arrived individuals were exposed to isolated and combined OW and OA conditions for 100 days, adjusting for the salinity gradients associated with upstream migration. A two-choice test was used to investigate migratory activity and shifts in preference towards freshwater environments. While OW decreased survival and increased migratory activity, OA appears to hinder migratory response, reducing the preference for riverine cues. Our results suggest that future conditions could potentially favour an early settlement of glass eels, reducing the proportion of fully migratory individuals. Further research into the effects of climate change on eel migration and habitat selection is needed to implement efficient conservation plans for this critically endangered species.

Continue reading ‘Ocean warming and acidification may challenge the riverward migration of glass eels’

Ocean acidification and warming affect skeletal mineralization in a marine fish

Ocean acidification and warming are known to alter, and in many cases decrease, calcification rates of shell and reef building marine invertebrates. However, to date, there are no datasets on the combined effect of ocean pH and temperature on skeletal mineralization of marine vertebrates, such as fishes. Here, the embryos of an oviparous marine fish, the little skate (Leucoraja erinacea), were developmentally acclimatized to current and increased temperature and CO2 conditions as expected by the year 2100 (15 and 20°C, approx. 400 and 1100 µatm, respectively), in a fully crossed experimental design. Using micro-computed tomography, hydroxyapatite density was estimated in the mineralized portion of the cartilage in jaws, crura, vertebrae, denticles and pectoral fins of juvenile skates. Mineralization increased as a consequence of high CO2 in the cartilage of crura and jaws, while temperature decreased mineralization in the pectoral fins. Mineralization affects stiffness and strength of skeletal elements linearly, with implications for feeding and locomotion performance and efficiency. This study is, to my knowledge, the first to quantify a significant change in mineralization in the skeleton of a fish and shows that changes in temperature and pH of the oceans have complex effects on fish skeletal morphology.

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Ocean acidification in the IPCC AR5 WG II

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