Posts Tagged 'oxygen'

Coastal acidification and deoxygenation enhance settlement but do not influence movement behavior of creeping polyps of the irukandji jellyfish, Alatina alata (cubozoa)

Highlights

  • Deoxygenation enhanced the survival of the creeping polyps of Alatina alata.

  • More creeping polyps settled under low pH and low dissolved O2 (DO) treatments than under normal pH and DO conditions.

  • Exposure to low pH and DO did not influence the number of tentacles, mobility or movement velocity of the creeping polyps.

  • The Irukandji jellyfish may persist in coastal areas with coastal deoxygenation and acidification.

Abstract

Deoxygenation and acidification co-occur in many coastal ecosystems because nutrient enrichment produces excess organic matter that intensifies aerobic respiration during decomposition, thereby depleting O2, increasing CO2 and lowering pH. Despite this link between coastal deoxygenation (CD) and acidification (CA), and evidence that both stressors pose a risk to marine fauna, few studies have examined the effects of these drivers in combination on marine animals including invertebrates. Here, we studied the individual and combined effects of CD (∼1.5 mg L−1 O2) and CA (∼7.7 pH) on the survival, number of tentacles, settlement and movement behaviours of creeping polyps of the Irukandji jellyfish, Alatina alata. Low DO increased the survival rate (17% more) of the creeping polyps. 12% more creeping polyps settled in low pH than ambient pH and 16.7% more settled in low DO than ambient DO treatment. Exposure to CA and CD did not influence the number of tentacles, mobility or movement velocity of the creeping polyps, but after 4 h exposure to the treatments, they moved approximately half as fast. Our results indicate that CD can enhance survival and settlement success, but CA does not intensify these outcomes on A. alata creeping polyps.

Continue reading ‘Coastal acidification and deoxygenation enhance settlement but do not influence movement behavior of creeping polyps of the irukandji jellyfish, Alatina alata (cubozoa)’

Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine diatom Thalassiosira pseudonana (Coscinodiscophyceae)

The marine diatom Thalassiosira pseudonana was grown in continuous culture systems to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO2 (pCO2) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 μmol photons · m−2 · s−1, respectively, of visible light), low and high pCO2 (400 and 1,000 μatm, respectively), nutrient limitation (nitrate‐limited and nutrient‐replete conditions), and temperatures of 10–32°C. Under nutrient‐replete conditions, there was no adverse effect of high pCO2 on growth rates at temperatures of 10–25°C. The response of the cells to high pCO2 was similar at low and high irradiance. At supraoptimal temperatures of 30°C or higher, high pCO2 depressed growth rates at both low and high irradiance. Under nitrate‐limited conditions, cells were grown at 38 ± 2.4% of their nutrient‐saturated rates at the same temperature, irradiance, and pCO2. Dark respiration rates consistently removed a higher percentage of production under nitrate‐limited versus nutrient‐replete conditions. The percentages of production lost to dark respiration were positively correlated with temperature under nitrate‐limited conditions, but there was no analogous correlation under nutrient‐replete conditions. The results suggest that warmer temperatures and associated more intense thermal stratification of ocean surface waters could lower net photosynthetic rates if the stratification leads to a reduction in the relative growth rates of marine phytoplankton, and at truly supraoptimal temperatures there would likely be a synergistic interaction between the stresses from temperature and high pCO2 (lower pH).

Continue reading ‘Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine diatom Thalassiosira pseudonana (Coscinodiscophyceae)’

Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta

Acidification and deoxygenation are two consequences of climate change that also co-occur in eutrophied coastal zones and can have deleterious effects on marine life. While the effects of hypoxia on marine herbivores have been well-studied, how ocean acidification combined with hypoxia affects herbivory is poorly understood. This study examined how herbivory and survival by the gastropod Lacuna vincta grazing on the macroalgae Ulva rigida was influenced by hypoxia and ocean acidification, alone and in combination, with and without food limitation. Experiments exposed L. vincta to a range of environmentally realistic dissolved oxygen (0.7 – 8 mg L–1) and pH (7.3 – 8.0 total scale) conditions for 3 – 72 h, with and without a starvation period and quantified herbivory and survival. While acidified conditions (pH < 7.4) reduced herbivory when combined with food limitation, low oxygen conditions (< 4 mg L–1) reduced herbivory and survival regardless of food supply. When L. vincta were starved and grazed in acidified conditions herbivory was additively reduced, whereas starvation and hypoxia synergistically reduced grazing rates. Overall, low oxygen had a more inhibitory effect on herbivory than low pH. Shorter exposure times (9, 6, and 3 h) were required to reduce grazing at lower DO levels (∼2.4, ∼1.6, and ∼0.7 mg L–1, respectively). Herbivory ceased entirely following a three-hour exposure to DO of 0.7 mg L–1 suggesting that episodes of diurnal hypoxia disrupt grazing by these gastropods. The suppression of herbivory in response to acidified and hypoxic conditions could create a positive feedback loop that promotes ‘green tides’ whereby reduced grazing facilitates the overgrowth of macroalgae that cause nocturnal acidification and hypoxia, further disrupting herbivory and promoting the growth of macroalgae. Such feedback loops could have broad implications for estuarine ecosystems where L. vincta is a dominant macroalgal grazer and will intensify as climate change accelerates.

Continue reading ‘Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta’

Physiological resilience of pink salmon to naturally occurring ocean acidification

Pacific salmon stocks are in decline with climate change named as a contributing factor. The North Pacific coast of British Columbia is characterized by strong temporal and spatial heterogeneity in ocean conditions with upwelling events elevating CO2 levels up to 10-fold those of pre-industrial global averages. Early life stages of pink salmon have been shown to be affected by these CO2 levels, and juveniles naturally migrate through regions of high CO2 during the energetically costly phase of smoltification. To investigate the physiological response of out-migrating wild juvenile pink salmon to these naturally occurring elevated CO2 levels, we captured fish in Georgia Strait, British Columbia and transported them to a marine lab (Hakai Institute, Quadra Island) where fish were exposed to one of three CO2 levels (850, 1500 and 2000 μatm CO2) for 2 weeks. At ½, 1 and 2 weeks of exposure, we measured their weight and length to calculate condition factor (Fulton’s K), as well as haematocrit and plasma [Cl]. At each of these times, two additional stressors were imposed (hypoxia and temperature) to provide further insight into their physiological condition. Juvenile pink salmon were largely robust to elevated CO2 concentrations up to 2000 μatm CO2, with no mortality or change in condition factor over the 2-week exposure duration. After 1 week of exposure, temperature and hypoxia tolerance were significantly reduced in high CO2, an effect that did not persist to 2 weeks of exposure. Haematocrit was increased by 20% after 2 weeks in the CO2 treatments relative to the initial measurements, while plasma [Cl] was not significantly different. Taken together, these data indicate that juvenile pink salmon are quite resilient to naturally occurring high CO2 levels during their ocean outmigration.

Continue reading ‘Physiological resilience of pink salmon to naturally occurring ocean acidification’

A regional vulnerability assessment for the Dungeness crab (Metacarcinus magister) to changing ocean conditions: insights from model projections and empirical experiments

Among global coastal regions, the Northern California Current System (N-CCS) is already experiencing effects from ocean acidification and hypoxia during the summer, primarily due to the region’s seasonal upwelling, current systems, and high productivity. Oxygen, pH, and temperature conditions are expected to become more stressful with continued fossil fuel emissions under global climate change, posing a serious threat to the region’s fisheries. N-CCS fishing communities rely heavily on the economically and culturally important Dungeness crab (Metacarcinus magister). The fishery is currently sustainably managed, but potential negative impacts from changing ocean conditions on Dungeness crab life stages and populations could have adverse effects for the fishery and the communities that rely on it. To quantify the vulnerability of Dungeness crab life stages and populations to predicted future conditions, both model projections and empirical experiments need to be employed. A semi-quantitative, life stage-specific framework was adapted here to assess the vulnerability of Dungeness crab to low pH, low dissolved oxygen, and high temperature under present and future projected conditions in the seasonally dynamic N-CCS. This was achieved using a combination of regional ocean models, species distribution maps, larval transport models, a population matrix model, and a literature review. This multi-faceted approach revealed that crab vulnerability to the three climate stressors will increase in the future (year 2100) under the most intense emissions scenario, with vulnerability to low oxygen being the most severe to the N-CCS population overall. Increases in vulnerability were largely driven by the adult life stage, which contributes the most to population growth. Empirical experiments demonstrated that adult crab respiration rates increase exponentially with temperature, potentially making this life stage more susceptible to hypoxia in the future. Together, this work provides novel insights into the effects of changing ocean conditions on Dungeness crab populations, which may help inform fishery management strategies.

Continue reading ‘A regional vulnerability assessment for the Dungeness crab (Metacarcinus magister) to changing ocean conditions: insights from model projections and empirical experiments’

Severe coastal hypoxia interchange with ocean acidification: an experimental perturbation study on carbon and nutrient biogeochemistry

Normally atmospheric CO2 is the major driver of ocean acidification (OA); however, local discharge/degradation of organic matter (OM) and redox reactions can exacerbate OA in coastal areas. In this work we study the response of nutrient and carbon systems to pH decrease in relation to hydrographically induced intermittent characteristics and examine scenarios for future ocean acidification in a coastal system. Laboratory microcosm experiments were conducted using seawater and surface sediment collected from the deepest part of Elefsis Bay; the pH was constantly being monitored while CO2 gas addition was adjusted automatically. In Elefsis Bay surface pCO2 is already higher than global present atmospheric values, while near the bottom pCO2 reaches 1538 μatm and carbonate saturation states were calculated to be around 1.5. During the experiment, in more acidified conditions, limited alkalinity increase was observed and was correlated with the addition of bicarbonates and OM. Ammonium oxidation was decelerated and a nitrification mechanism was noticed, despite oxygen deficiency, paralleled by reduction of Mn-oxides. Phosphate was found significantly elevated for the first time in lower pH values, without reprecipitating after reoxygenation; this was linked with Fe(II) oxidation and Fe(III) reprecipitation without phosphate adsorption affecting both available dissolved phosphate and (dissolved inorganic nitrogen) DIN:DIP (dissolved inorganic phosphate)ratio.

Continue reading ‘Severe coastal hypoxia interchange with ocean acidification: an experimental perturbation study on carbon and nutrient biogeochemistry’

Changes in biofilm bacterial communities in response to combined effects of hypoxia, ocean acidification and nutrients from aquaculture activity in Three Fathoms Cove

Highlights

•Combined occurrence of hypoxia, acidification and nutrients increased biofilm bacterial diversity and richness

•Elevated nutrients, and depleted oxygen and pH levels resulted in different bacterial community composition

•Higher abundance of Flavobacteriales, Epsilonproteobacteria and Vibrionales, but less Oceanospirillales and Alteromonadales

•Suggests the identities of bacterial groups affected under the ocean trend of pollution, deoxygenation and acidification

Abstract

Anthropogenic nutrient enrichment results in hypoxia, ocean acidification and elevated nutrients (HOAN) in coastal environments throughout the world. Here, we examined the composition of biofilm bacterial communities from a nutrient-excessive fish farm with low dissolved oxygen (DO) and pH levels using 16S rRNA gene sequencing. HOAN was accompanied by higher bacterial diversity and richness, and resulted in an altered community composition than the control site. HOAN resulted in more Flavobacteriales, Rhizobiales, Epsilonproteobacteria and Vibrionales, but less Oceanospirillales and Alteromonadales. Photobacterium sp. and Vibrio sp. were mostly found to be exclusive to HOAN conditions, suggesting that HOAN could possibly proliferate the presence of these potential pathogens. Our study suggests the complexity of bacterial communities to hypoxia and acidification in response to increased nutrient loads, along with identities of nutrient, oxygen and pH-susceptible bacterial groups that are most likely affected under this ocean trend.

Continue reading ‘Changes in biofilm bacterial communities in response to combined effects of hypoxia, ocean acidification and nutrients from aquaculture activity in Three Fathoms Cove’

Ocean acidification, hypoxia and warming impair digestive parameters of marine mussels

Highlights

•Low pH, low DO and high temperature showed drastic effects on digestive enzyme activities.

•Low pH, low DO and high temperature synergistically reduced digestive enzyme activities.

•Lysozyme showed increased and then decreased activities with time.

•Combinations of low pH, low DO and high temperature showed more severe effects on digestive enzymes than single factors.

•Hypoxia and high temperature showed similar effects on digestive enzyme activities.

Abstract

Global change and anthropogenic activities have driven marine environment changes dramatically during the past century, and hypoxia, acidification and warming have received much attention recently. Yet, the interactive effects among these stressors on marine organisms are extremely complex and not accurately clarified. Here, we evaluated the combined effects of low dissolved oxygen (DO), low pH and warming on the digestive enzyme activities of the mussel Mytilus coruscus. In this experiment, mussels were exposed to eight treatments, including two degrees of pH (8.1, 7.7), DO (6, 2 mg/l) and temperature (30 °C and 20 °C) for 30 days. Amylase (AMS), lipase (LPS), trypsin (TRY), trehalase (TREH) and lysozyme (LZM) activities were measured in the digestive glands of mussels. All the tested stress conditions showed significant effects on the enzymatic activities. AMS, LPS, TRY, TREH showed throughout decreased trend in their activities due to low pH, low DO, increased temperature and different combinations of these three stressors with time but LZM showed increased and then decreased trend in their activities. Hypoxia and warming showed almost similar effects on the enzymatic activities. PCA showed a positive correlation among all measured biochemical parameters. Therefore, the fitness of mussel is likely impaired by such marine environmental changes and their population may be affected under the global change scenarios.

Continue reading ‘Ocean acidification, hypoxia and warming impair digestive parameters of marine mussels’

The effect of climate change on the escape kinematics and performance of fishes: implications for future predator–prey interactions

Climate change can have a pronounced impact on the physiology and behaviour of fishes. Notably, many climate change stressors, such as global warming, hypoxia and ocean acidification (OA), have been shown to alter the kinematics of predator–prey interactions in fishes, with potential effects at ecological levels. Here, we review the main effects of each of these stressors on fish escape responses using an integrative approach that encompasses behavioural and kinematic variables. Elevated temperature was shown to affect many components of the escape response, including escape latencies, kinematics and maximum swimming performance, while the main effect of hypoxia was on escape responsiveness and directionality. OA had a negative effect on the escape response of juvenile fish by decreasing their directionality, responsiveness and locomotor performance, although some studies show no effect of acidification. The few studies that have explored the effects of multiple stressors show that temperature tends to have a stronger effect on escape performance than OA. Overall, the effects of climate change on escape responses may occur through decreased muscle performance and/or an interference with brain and sensory functions. In all of these cases, since the escape response is a behaviour directly related to survival, these effects are likely to be fundamental drivers of changes in marine communities. The overall future impact of these stressors is discussed by including their potential effects on predator attack behaviour, thereby allowing the development of potential future scenarios for predator–prey interactions.

Continue reading ‘The effect of climate change on the escape kinematics and performance of fishes: implications for future predator–prey interactions’

Single and combined effects of the “deadly trio” hypoxia, hypercapnia and warming on the cellular metabolism of the great scallop Pecten maximus

Highlights

• Gill metabolism of king scallops is affected by singly and combined climate drivers

• Scallops were most tolerant to warming plus hypercapnia and were most susceptible to oxygen reduction

• Metabolic analysis revealed alterations in mitochondrial energy metabolism most pronounced in scallops exposed to high temperatures and Deadly trio (Warming + hypercapnia + hypoxia)

• Imbalances in energy metabolism decrease the upper thermal tolerance of P. maximus

Abstract

In the ocean the main climate drivers affecting marine organisms are warming, hypercapnia, and hypoxia. We investigated the acute effects of warming (W), warming plus hypercapnia (WHc, ~1800 μatm CO2), warming plus hypoxia (WHo, ~12.1 kPa O2), and a combined exposure of all three drivers (Deadly Trio, DT) on king scallops (Pecten maximus). All exposures started at 14 °C and temperature was increased by 2 °C once every 48 h until the lethal temperature was reached (28 °C). Gill samples were taken at 14 °C, 18 °C, 22 °C, and 26 °C and analyzed for their metabolic response by 1H-nuclear magnetic resonance (NMR) spectroscopy. Scallops were most tolerant to WHc and most susceptible to oxygen reduction (WHo and DT). In particular under DT, scallops’ mitochondrial energy metabolism was affected. Changes became apparent at 22 °C and 26 °C involving significant accumulation of glycogenic amino acids (e.g. glycine and valine) and anaerobic end-products (e.g. acetic acid and succinate). In line with these observations the LT50 was lower under the exposure to DT (22.5 °C) than to W alone (~ 25 °C) indicating a narrowing of the thermal niche due to an imbalance between oxygen demand and supply.

Continue reading ‘Single and combined effects of the “deadly trio” hypoxia, hypercapnia and warming on the cellular metabolism of the great scallop Pecten maximus’


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