Posts Tagged 'salinity'

Physiological trade-offs, acid-base balance and ion-osmoregulatory plasticity in European sea bass (Dicentrarchus labrax) juveniles under complex scenarios of salinity variation, ocean acidification and high ammonia challenge

Highlights

• Ocean acidification (OA) is becoming a serious threat to the marine ecosystem.

• OA can co-occur with other perturbations including salinity reduction and high ammonia.

• Interactive effects of these three stressers were evaluated on performance of European sea bass.

• Physiological, ion-osmoregulatory and gene-expression responses were modulated differentially under experimental conditions.

• Fish became more vulnerable to OA and ammonia toxicity at low salinities.

Abstract

In this era of global climate change, ocean acidification is becoming a serious threat to the marine ecosystem. Despite this, it remains almost unknown how fish will respond to the co-occurrence of ocean acidification with other conventional environmental perturbations typically salinity fluctuation and high ammonia threat. Therefore, the present work evaluated the interactive effects of elevated pCO2, salinity reduction and high environmental ammonia (HEA) on the ecophysiological performance of European sea bass (Dicentrarchus labrax). Fish were progressively acclimated to seawater (32 ppt), to brackish water (10 ppt) and to hyposaline water (2.5 ppt). Following acclimation to different salinities for at least two weeks, fish were exposed to CO2-induced water acidification representing present-day (control pCO2, 400 μatm, LoCO2) and future (high pCO2, 1000 μatm, HiCO2) sea-surface CO2 level for 3, 7 and 21 days. At the end of each exposure period, fish were challenged with HEA for 6 h (1.18 mM representing 50% of 96 h LC50). Results show that, in response to the individual HiCO2 exposure, fish within each salinity compensated for blood acidosis. Fish subjected to HiCO2 were able to maintain ammonia excretion rate (Jamm) within control levels, suggesting that HiCO2 exposure alone had no impact on Jamm at any of the salinities. For 32 and 10 ppt fish, up-regulated expression of Na+/K+-ATPase was evident in all exposure groups (HEA, HiCO2 and HEA/HiCO2 co-exposed), whereas Na+/K+/2Cl− co-transporter was up-regulated mainly in HiCO2 group. Plasma glucose and lactate content were augmented in all exposure conditions for all salinity regimes. During HEA and HEA/HiCO2, Jamm was inhibited at different time points for all salinities, which resulted in a significant build-up of ammonia in plasma and muscle. Branchial expressions of Rhesus glycoproteins (Rhcg isoforms and Rhbg) were upregulated in response to HiCO2 as well as HEA at 10 ppt, with a more moderate response in 32 ppt groups. Overall, our findings denote that the adverse effect of single exposures of ocean acidification or HEA is exacerbated when present together, and suggests that fish are more vulnerable to these environmental threats at low salinities.

Continue reading ‘Physiological trade-offs, acid-base balance and ion-osmoregulatory plasticity in European sea bass (Dicentrarchus labrax) juveniles under complex scenarios of salinity variation, ocean acidification and high ammonia challenge’

Toxic algae silence physiological responses to multiple climate drivers in a tropical marine food chain

Research on the effects of climate change in the marine environment continues to accelerate, yet we know little about the effects of multiple climate drivers in more complex, ecologically relevant settings – especially in sub-tropical and tropical systems. In marine ecosystems, climate change (warming and freshening from land run-off) will increase water column stratification which is favorable for toxin producing dinoflagellates. This can increase the prevalence of toxic microalgal species, leading to bioaccumulation of toxins by filter feeders, such as bivalves, with resultant negative impacts on physiological performance. In this study we manipulated multiple climate drivers (warming, freshening, and acidification), and the availability of toxic microalgae, to determine their impact on the physiological health, and toxin load of the tropical filter-feeding clam, Meretrix meretrix. Using a structural equation modeling (SEM) approach, we found that exposure to projected marine climates resulted in direct negative effects on metabolic and immunological function and, that these effects were often more pronounced in clams exposed to multiple, rather than single climate drivers. Furthermore, our study showed that these physiological responses were modified by indirect effects mediated through the food chain. Specifically, we found that when bivalves were fed with a toxin-producing dinoflagellate (Alexandrium minutum) the physiological responses, and toxin load changed differently and in a non-predictable way compared to clams exposed to projected marine climates only. Specifically, oxygen consumption data revealed that these clams did not respond physiologically to climate warming or the combined effects of warming, freshening and acidification. Our results highlight the importance of quantifying both direct and, indirect food chain effects of climate drivers on a key tropical food species, and have important implications for shellfish production and food safety in tropical regions.

Continue reading ‘Toxic algae silence physiological responses to multiple climate drivers in a tropical marine food chain’

Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues

Florida Bay is home to a network of shallow mud-banks which act as barriers to circulation creating small basins that are often subject to extremes in temperature and salinity. Florida bay is also important juvenile habitat for the Caribbean spiny lobster Panulirus argus. While our understanding of the effect of environmental changes on the survival, growth, and movement of spiny lobsters is growing, the effect on their chemosensory abilities has not yet been investigated. Lobsters rely heavily on chemical cues for many biological and ecological activities, and here we report on the effect of extreme environmental events in temperature (32 °C), salinity (45ppt), and pH (7.65 pH) on social behavior and sheltering preference in P. argus. Under normal conditions, chemical cues from conspecifics are used by spiny lobsters to identify suitable shelter and cues from stone crabs and diseased individuals are used to determine shelters to be avoided. In all altered conditions, lobsters lost the ability to aggregate with conspecifics and avoid stone crabs and diseased conspecifics. Thus, seasonal extreme events, and potentially future climate change conditions, alter the chemosensory-driven behavior of P. argus and may result in decreased survivorship due to impaired shelter selection or other behaviors.

Continue reading ‘Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues’

Hyposalinity tolerance inthecoccolithophorid Emiliania huxleyi under the influence of ocean acidification involves enhanced photosynthetic performance

While seawater acidification induced by elevated CO2 is known to impact coccolithophores, the effects in combination with decreased salinity caused by sea ice melting and/or hydrological events have not been documented. Here we show the combined effects of seawater acidification and reduced salinity on growth, photosynthesis and calcification of Emiliania huxleyi grown at 2 CO2 concentrations (low CO2 LC: 400 μatm; high CO2 HC: 1000 μatm) and 3 levels of salinity (25, 30 and 35 ‰). A decrease of salinity from 35 to 25‰ increased growth rate, cell size and effective photochemical efficiency under both LC or HC. Calcification rates were relatively insensitive to combined effects of salinity and OA treatment but were highest under 3 5‰ and HC conditions, with higher ratios of calcification to photosynthesis (C : P) in the cells grown under 35 ‰ compared with those grown at 25 ‰. In addition, elevated dissolved inorganic carbon (DIC) concentration at the salinity of 35 ‰ stimulated its calcification. In contrast, photosynthetic carbon fixation increased almost linearly with decreasing salinity, regardless of the pCO2 treatments. When subjected to short-term exposure to high light, the low-salinity-grown cells showed the highest photochemical effective quantum yield with the highest repair rate, though HC treatment enhanced PSII damage rate. Our results suggest Emiliania huxleyi can tolerate low salinity plus acidification conditions by up-regulating its photosynthetic performance together with a relatively insensitive calcification response, which may help it better adapt to future ocean global environmental changes, especially in the coastal areas of high latitudes.

Continue reading ‘Hyposalinity tolerance inthecoccolithophorid Emiliania huxleyi under the influence of ocean acidification involves enhanced photosynthetic performance’

Feeding plasticity more than metabolic rate drives the productivity of economically important filter feeders in response to elevated CO2 and reduced salinity

Climate change driven alterations in salinity and carbonate chemistry are predicted to have significant implications particularly for northern costal organisms, including the economically important filter feeders Mytilus edulis and Ciona intestinalis. However, despite a growing number of studies investigating the biological effects of multiple environmental stressors, the combined effects of elevated pCO2 and reduced salinity remain comparatively understudied. Changes in metabolic costs associated with homeostasis and feeding/digestion in response to environmental stressors may reallocate energy from growth and reproduction, affecting performance. Although these energetic trade-offs in response to changes in routine metabolic rates have been well demonstrated fewer studies have investigated how these are affected by changes in feeding plasticity. Consequently, the present study investigated the combined effects of 26 days’ exposure to elevated pCO2 (500 µatm and 1000 µatm) and reduced salinity (30, 23, and 16) on the energy available for growth and performance (Scope for Growth) in M. edulis and C. intestinalis, and the role of metabolic rate (oxygen uptake) and feeding plasticity [clearance rate (CR) and absorption efficiency] in this process. In M. edulis exposure to elevated pCO2 resulted in a 50% reduction in Scope for Growth. However, elevated pCO2 had a much greater effect on C. intestinalis, with more than a 70% reduction in Scope for Growth. In M. edulis negative responses to elevated pCO2 are also unlikely be further affected by changes in salinity between 16 and 30. Whereas, under future predicted levels of pCO2C. intestinalis showed 100% mortality at a salinity of 16, and a >90% decrease in Scope for Growth with reduced biomass at a salinity of 23. Importantly, this work demonstrates energy available for production is more dependent on feeding plasticity, i.e. the ability to regulate CR and absorption efficiency, in response to multiple stressors than on more commonly studied changes in metabolic rates.

Continue reading ‘Feeding plasticity more than metabolic rate drives the productivity of economically important filter feeders in response to elevated CO2 and reduced salinity’

Sensitivity to near-future CO2 conditions in marine crabs depends on their compensatory capacities for salinity change

Marine crabs inhabit shallow coastal/estuarine habitats particularly sensitive to climate change, and yet we know very little about the diversity of their responses to environmental change. We report the effects of a rarely studied, but increasingly prevalent, combination of environmental factors, that of near-future pCO2 (~1000 µatm) and a physiologically relevant 20% reduction in salinity. We focused on two crab species with differing abilities to cope with natural salinity change, and revealed via physiological and molecular studies that salinity had an overriding effect on ion exchange in the osmoregulating shore crab, Carcinus maenas. This species was unaffected by elevated CO2, and was able to hyper-osmoregulate and maintain haemolymph pH homeostasis for at least one year. By contrast, the commercially important edible crab, Cancer pagurus, an osmoconformer, had limited ion-transporting capacities, which were unresponsive to dilute seawater. Elevated CO2 disrupted haemolymph pH homeostasis, but there was some respite in dilute seawater due to a salinity-induced metabolic alkalosis (increase in HCO3− at constant pCO2). Ultimately, Cancer pagurus was poorly equipped to compensate for change, and exposures were limited to 9 months. Failure to understand the full spectrum of species-related vulnerabilities could lead to erroneous predictions of the impacts of a changing marine climate.

Continue reading ‘Sensitivity to near-future CO2 conditions in marine crabs depends on their compensatory capacities for salinity change’

Effects of ocean acidification on salinity tolerance and seawater growth of Atlantic salmon Salmo salar smolts

Human activity has resulted in increasing atmospheric carbon dioxide (CO2), which will result in reduced pH and higher levels of CO2 in the ocean, a process known as ocean acidification. Understanding the effects of ocean acidification (OA) on fishes will be important to predicting and mitigating its consequences. Anadromous species such as salmonids may be especially at risk because of their rapid movements between fresh water and seawater, which could minimize their ability to acclimate. In the present study, we examine the effect of future OA on the salinity tolerance and early seawater growth of Atlantic salmon Salmo salar smolts. Exposure to 610 and 1010 μatm CO2 did not alter salinity tolerance but did result in slightly lower plasma chloride levels in smolts exposed to seawater compared with controls (390 μatm). Gill Na+–K+‐ATPase activity, plasma cortisol, glucose and haematocrit after seawater exposure were not altered by elevated CO2. Growth rate in the first 2 weeks of seawater exposure was greater at 1010 μatm CO2 than under control conditions. This study of the effects of OA on S. salar during the transition from fresh water to seawater indicates that elevated CO2 is not likely to affect osmoregulation negatively and may improve early growth in seawater.

Continue reading ‘Effects of ocean acidification on salinity tolerance and seawater growth of Atlantic salmon Salmo salar smolts’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,242,876 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book