Posts Tagged 'salinity'

Anthropogenic impacts on mangrove and saltmarsh communities in eastern Australia

The global phenomenon of mangrove encroachment into saltmarshes has been observed across five continents. It has been proposed that this encroachment is driven in part by rising atmospheric CO2 concentration and reduced salinity in saltmarshes resulting from rising sea levels enhancing the establishment success of mangrove seedlings. However, this is yet to be empirically tested at the community-level. In this study, we examined the effect of CO2 and salinity on seedling growth of two mangrove species, Aegiceras corniculatum and Avicennia
marina, grown individually and in a model saltmarsh community in a glasshouse experiment. We found that the shoot (210%) and root (91%) biomass of the saltmarsh species was significantly greater under elevated CO2. As a result, both mangrove species experienced a stronger competitive effect from the saltmarsh species under elevated CO2. Nevertheless, A. marina seedlings produced on average 48% more biomass under elevated CO2 when grown in competition with the saltmarsh species which they used to grow taller suggesting they were light
limited. In contrast, A. corniculatum growth did not significantly differ between CO2 treatments. However, it had on average 36% greater growth under seawater salinity compared to hypersaline conditions. Avicenna marina seedlings were not affected by salinity. From these results, we suggest that although CO2 and salinity are not universal drivers determining saltmarsh-mangrove boundaries, it is likely that rising atmospheric CO2 concentration and reduced salinity associated with sea level rise will enhance the establishment success of mangrove seedlings in saltmarshes, which may facilitate mangrove encroachment in the future.

Continue reading ‘Anthropogenic impacts on mangrove and saltmarsh communities in eastern Australia’

Hsp70 knockdown reduced the tolerance of Litopenaeus vannamei post larvae to low pH and salinity

Highlights

• Injection of the white-leg shrimp with Hsp70 dsRNA eliminated Hsp70 mRNA and protein in post-larvae but had no apparent effect on survival.

• However, the survival of post larvae lacking Hsp70, as compared to those containing the heat shock protein, was reduced more than two-fold 48 h after exposure to low salinity and pH, strongly indicating that Hsp70 is required for protection against these abiotic stressors.

• This is the first time to our knowledge that RNAi has been used to demonstrate a role for Hsp70 in protecting P. vannamei post larvae against salinity and pH stress, an effect undoubtedly due to the importance Hsp70 assumes in maintaining protein homeostasis within cells.

Abstract

To better understand stress tolerance of the White leg shrimp, Litopenaeus vannamei, RNA interference (RNAi) was used to assess the role of the molecular chaperone, Hsp70 in protecting post larvae against low pH and salinity. As revealed by SDS-polyacrylamide gel electrophoresis and immunoprobing of western blots, injection of L. vannamei post larvae with Hsp70 and Hsc70 dsRNA reduced Hsp70 but had no apparent effect on survival. However, the survival of post larvae lacking Hsp70, as compared to those containing the heat shock protein, was reduced more than two-fold 48 h after exposure to low salinity and pH, strongly indicating that Hsp70 is required for protection against these abiotic stressors. This is the first time to our knowledge that RNAi has been used to demonstrate a role for Hsp70 in protecting L. vannamei post larvae against salinity and pH stress, an effect undoubtedly due to the importance Hsp70 assumes in maintaining protein homeostasis within cells. Information generated in this work provides further understanding of Hsp70 function in the stress response of Penaeid shrimp and will assist in the development of strategies to mitigate abiotic stresses experienced by aquatic invertebrates during aquaculture.

Continue reading ‘Hsp70 knockdown reduced the tolerance of Litopenaeus vannamei post larvae to low pH and salinity’

Future CO2-induced ocean acidification enhances resilience of a green tide alga to low-salinity stress

To understand how Ulva species might respond to salinity stress during future ocean acidification we cultured a green tide alga Ulva linza at various salinities (control salinity, 30 PSU; medium salinity, 20 PSU; low salinity, 10 PSU) and CO2 concentrations (400 and 1000 ppmv) for over 30 days. The results showed that, under the low salinity conditions, the thalli could not complete its whole life cycle. The specific growth rate (SGR) of juvenile thalli decreased significantly with reduced salinity but increased with a rise in CO2. Compared to the control, medium salinity also decreased the SGR of adult thalli at low CO2 but did not affect it at high CO2. Similar patterns were also found in relative electron transport rate (rETR), non-photochemical quenching, saturating irradiance, and Chl b content. Although medium salinity reduced net photosynthetic rate and maximum rETR at each CO2 level, these negative effects were significantly alleviated at high CO2 levels. In addition, nitrate reductase activity was reduced by medium salinity but enhanced by high CO2. These findings indicate that future ocean acidification would enhance U. linza’s tolerance to low salinity stress and may thus facilitate the occurrence of green tides dominated by U. linza.

Continue reading ‘Future CO2-induced ocean acidification enhances resilience of a green tide alga to low-salinity stress’

An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors

Environmental biomarkers, also known as early warning signals, have increasingly
become a subject of interest in environmental studies. The common sea star, Archaster typicus, found in shallow sandy habitats associated with coral reefs in Singapore, was utilised to study the effects of varying treatment conditions of salinity, temperature and pH. Treatment conditions were derived from predicted future scenarios of thermal and ocean acidification conditions. Experiments were conducted to determine physiological responses of sea stars that were subjected to treatments over 24h (acute) and 120h (chronic) exposures. The biomarker responses examined included righting behaviour (time taken to right after being overturned), burrowing time and feeding responses (time
taken to close stomach/mouth plate) in experimental sea stars. To validate results of physiological biomarkers, two other biomarker responses were measured from coelomic fluid extracted from the experimental sea stars. These were the cellular lysosome integrity response (Neutral Red Retention time, NRRT) and the biochemical Ferric Reducing Antioxidant Power (FRAP) assay. In acute exposure experiments, results indicated that sea stars exhibited significant differences in physiological responses under various salinity, temperature and pH treatments. At chronic exposure regimes, lethal effects were more evident, with higher mortality rates observed in all salinity and temperature treatment regimes. Results from salinity treatments showed that physiological responses in sea stars were significantly impaired at treatments of 15‰ and 50‰ salinities. Significant results were observed in NRRT and burrowing behavioural assays in temperature treatments. Treatments with pH of 7.4 and 7.2 at the acute exposure duration resulted in a significant impairment of righting ability. The acute and chronic effects of salinity fluctuations, ocean warming and acidification on A
2 typicus were most consistently observed in the righting and burrowing behaviour assays. This indication of reduced fitness together with reduced cellular responses show a reduction in survival ability in the sea star under low salinity, high temperature and low pH conditions. Further studies could thus help us understand the effects of global warming on the physiology of organisms in various shallow water habitats.

Continue reading ‘An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors’

Sperm motility of oysters from distinct populations differs in response to ocean acidification and freshening

Species’ responses to climate change will reflect variability in the effects of physiological selection that future conditions impose. Here, we considered the effects of ocean acidification (increases in pCO2; 606, 925, 1250 µatm) and freshening (reductions in salinity; 33, 23, 13 PSU) on sperm motility in oysters (Crassostrea gigas) from two populations (one recently invaded, one established for 60+ years). Freshening reduced sperm motility in the established population, but this was offset by a positive effect of acidification. Freshening also reduced sperm motility in the recently invaded population, but acidification had no effect. Response direction, strength, and variance differed among individuals within each population. For the established population, freshening increased variance in sperm motility, and exposure to both acidification and freshening modified the performance rank of males (i.e. rank motility of sperm). In contrast, for the recently invaded population, freshening caused a smaller change in variance, and male performance rank was broadly consistent across treatments. That inter-population differences in response may be related to environmental history (recently invaded, or established), indicates this could influence scope for selection and adaptation. These results highlight the need to consider variation within and among population responses to forecast effects of multiple environmental change drivers.

Continue reading ‘Sperm motility of oysters from distinct populations differs in response to ocean acidification and freshening’

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’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book