Posts Tagged 'physiology'



Environmental controls on pteropod ecology and physiology along the Western Antarctic Peninsula

Pteropods (pelagic snails) are ubiquitous zooplankton in the Southern Ocean and abundant along the Western Antarctic Peninsula (WAP), one of the most rapidly warming regions on the planet. They are important prey for higher trophic levels, grazers of phytoplankton, and contribute to particulate organic and inorganic carbon export. Pteropods are heralded as bioindicators of ecosystem health due to the vulnerability of their aragonitic shells under ocean acidification conditions, which could greatly affect their abundances in the future. Despite their importance within Antarctic food webs, few studies have analyzed the effects of climate change on pteropod physiology and biogeography in the Southern Ocean. I utilized zooplankton net tows and sediment trap samples collected as part of the Palmer Antarctica Long Term Ecological Research (PAL LTER) program to determine long-term changes in pteropod biogeography and phenology (life history). I also conducted shipboard experiments on PAL LTER research cruises to analyze the effects of shifting temperature and food conditions on pteropod metabolism. Lastly, to examine WAP pteropod feeding ecology, I utilized high-throughput sequencing techniques and analyzed pteropod gut contents at an unprecedented taxonomic resolution. Pteropod populations along the WAP from 1993-2017 either remained stable (shelled pteropods) or increased (non-shelled pteropods) and were most strongly controlled by La Niña conditions the year prior, which led to warmer, ice-free waters. There was a weak relationship between pteropod abundance and carbonate chemistry, and no detectable long-term trend in carbonate chemistry parameters (i.e., aragonite saturation), thus ocean acidification is not presently a factor influencing WAP pteropod abundance. More open-water areas the year prior also increased growth rates of the shelled pteropod, Limacina helicina antarctica, and caused earlier time of appearance in the PAL LTER sediment trap. There was considerable interannual variability in the time of appearance of a new pteropod cohort, which ranged from year day 22 to 255, but no long-term, directional change in time of appearance or growth rate. The effects of warming seawater temperatures and shifting food availability on L. h. antarctica metabolism revealed that highest respiration and usually highest excretion rates occurred under higher temperatures, but the effect of food concentration was more limited. The proportion of dissolved organic matter to total organic and inorganic dissolved constituents was high and the metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which can directly affect phytoplankton growth and bacterial production in the WAP. Analysis of L. h. antarctica gut contents revealed its microbiome for the first time with Mollicutes bacteria the most abundant prokaryote. Pteropods were mainly herbivorous in summer, consuming predominantly diatoms but also supplementing their diet with microzooplankton such as ciliates. My dissertation shows that pteropods along the WAP are sensitive to changes in the environment from daily to interannual time scales. These insights into the metabolic and ecologic responses of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.

Continue reading ‘Environmental controls on pteropod ecology and physiology along the Western Antarctic Peninsula’

Physiological responses of Skeletonema costatum to the interactions of seawater acidification and combination of photoperiod and temperature

Ocean acidification (OA), which is a major environmental change caused by increasing atmospheric CO2, has considerable influences on marine phytoplankton. But few studies have investigated interactions of OA and seasonal changes in temperature and photoperiod on marine diatoms. In the present study, a marine diatom Skeletonema costatum was cultured under two different CO2 levels (LC, 400 μatm; HC, 1000 μatm) and three different combinations of temperature and photoperiod length (8:16 L:D with 5 ℃, 12:12 L:D with 15 ℃, 16:8 L:D with 25 ℃), simulating different seasons in typical temperate oceans, to investigate the combined effects of these factors. The results showed that specific growth rate of S. costatum increased with increasing temperature and daylength. However, OA showed contrasting effects on growth and photosynthesis under different combinations of temperature and daylength: while positive effects of OA were observed under spring and autumn conditions, it significantly decreased growth (11 %) and photosynthesis (21 %) in winter. In addition, low temperature and short daylength decreased the proteins of PSII (D1, CP47 and RubcL) at ambient pCO2 level, while OA alleviated the negative effect. These data indicated that future ocean acidification may show differential effects on diatoms in different cluster of other factors.

Continue reading ‘Physiological responses of Skeletonema costatum to the interactions of seawater acidification and combination of photoperiod and temperature’

Understanding the metabolic capacity of Antarctic fishes to acclimate to future ocean conditions

Antarctic fishes have evolved under stable, extreme cold temperatures for millions of years. Adapted to thrive in the cold environment, their specialized phenotypes will likely render them particularly susceptible to future ocean warming and acidification as a result of climate change. Moving from a period of stability to one of environmental change, species persistence will depend on maintaining energetic equilibrium, or sustaining the increased energy demand without compromising important biological functions such as growth and reproduction. Metabolic capacity to acclimate, marked by a return to metabolic equilibrium through physiological compensation of resting metabolic rate (RMR), will likely determine which species will be better poised to cope with shifts in environmental conditions. Focusing on the suborder Notothenioidei, a dominant group of Antarctic fishes, and in particular 4 well-studied species, Trematomus bernacchii, Pagothenia borchgrevinki, Notothenia rossii and N. coriiceps, we discuss metabolic acclimation potential to warming and CO2-acidification using an integrative and comparative framework. There are species-specific differences in the physiological compensation of RMR during warming and the duration of acclimation time required to achieve compensation; for some species RMR fully recovered within 3.5 weeks of exposure, such as P. borchgrevinki, while for other species, such as N. coriiceps, RMR remained significantly elevated past 9 weeks of exposure. In all instances, added exposure to increased PCO2, further compromised the ability of species to return RMR to pre-exposure levels. The period of metabolic imbalance, marked by elevated RMR, was underlined by energetic disturbance and elevated energetic costs, which shifted energy away from fitness-related functions, such as growth. In T. bernacchii and N. coriiceps, long duration of elevated RMR impacted condition factor and/or growth rate. Low growth rate can affect development and ultimately the timing of reproduction, severely compromising the species’ survival potential and the biodiversity of the notothenioid lineage. Therefore, the ability to achieve full compensation of RMR, and in a short-time frame, in order to avoid long term consequences of metabolic imbalance, will likely be an important determinant in a species’ capacity to persist in a changing environment. Much work is still required to develop our understanding of the bioenergetics of Antarctic fishes in the face of environmental change, and a targeted approach of nesting a mechanistic focus in an ecological and comparative framework will better aid our predictions on the effect of global climate change on species persistence in the polar regions.

Continue reading ‘Understanding the metabolic capacity of Antarctic fishes to acclimate to future ocean conditions’

Inorganic carbon uptake strategies in coralline algae: plasticity across evolutionary lineages under ocean acidification and warming

Highlights

• Ambient diffusive CO2 use of reef-building crustose coralline algae ranges from 35 to 65%.

• Algae largely maintain or increase bicarbonate use under ocean acidification and warming.

• Maintained or increased bicarbonate use is associated with sustained metabolic performance.

• Lineage predicts inorganic carbon uptake strategy.

• Proposed initial framework for inorganic carbon uptake strategies in crustose coralline algae.

Abstract

Dissolved inorganic carbon (DIC) assimilation is essential to the reef-building capacity of crustose coralline algae (CCA). Little is known, however, about the DIC uptake strategies and their potential plasticity under ongoing ocean acidification (OA) and warming. The persistence of CCA lineages throughout historical oscillations of pCO2 and temperature suggests that evolutionary history may play a role in selecting for adaptive traits. We evaluated the effects of pCO2 and temperature on the plasticity of DIC uptake strategies and associated energetic consequences in reef-building CCA from different evolutionary lineages. We simulated past, present, moderate (IPCC RCP 6.0) and high pCO2 (RCP 8.5) and present and high (RCP 8.5) temperature conditions and quantified stable carbon isotope fractionation (13ε), organic carbon content, growth and photochemical efficiency. All investigated CCA species possess CO2-concentrating mechanisms (CCMs) and assimilate CO2 via diffusion to varying degrees. Under OA and warming, CCA either increased or maintained CCM capacity, which was associated with overall neutral effects on metabolic performance. More basal taxa, Sporolithales and Hapalidiales, had greater capacity for diffusive CO2 use than Corallinales. We suggest that CCMs are an adaptation that supports a robust carbon physiology and are likely responsible for the endurance of CCA in historically changing oceans.

Continue reading ‘Inorganic carbon uptake strategies in coralline algae: plasticity across evolutionary lineages under ocean acidification and warming’

Physiological and molecular responses to ocean acidification among strains of a model diatom

Differential responses of diatoms, an important group of marine primary producers to ocean acidification, have been well documented. However, studies so far are based on limited representative strains from key species. Investigation of strain level responses will help us better understand the contrasting discrepancy in diatom responses to ocean acidification. Here, we selected four strains of the model diatom Phaeodactylum tricornutum isolated from different regions of the global ocean, representing all genotypes based on internal transcribed spacer 2 sequences, and investigated strain‐specific responses to ocean acidification. In response to ocean acidification, changes in carbon metabolism varied among strains, although no significant effects of ocean acidification on growth rates or pigments were observed in any strains. The expression of genes encoding plasma membrane bicarbonate transporters was downregulated in strain Pt4, reflecting a potential decrease in active urn:x-wiley:00243590:media:lno11565:lno11565-math-0001 uptake, which was not observed in the other strains. Reduction of CO2 concentrating mechanism efficiency was also indicated by the regulated expression of genes encoding carbonic anhydrases that catalyze the interconversion of urn:x wiley:00243590:media:lno11565:lno11565-math-0002 and CO2 in the pyrenoids and pyrenoid‐penetrating thylakoid, which exhibited different patterns among the strains. Under ocean acidification conditions, C4‐like metabolism appeared to redistribute carbon flux to gluconeogenesis in strain Pt1, and lipid synthesis in strains Pt8 and Pt11, rather than participating in net photosynthetic carbon fixation. These variations were incompletely correlated with phylogenetic relationship in different strains, implying that the habitat‐adapted imprints of the different strains could also be responsible for their differential responses to ocean acidification.

Continue reading ‘Physiological and molecular responses to ocean acidification among strains of a model diatom’

Inorganic carbon utilization of tropical calcifying macroalgae and the impacts of intensive mariculture-derived coastal acidification on the physiological performance of the rhodolith Sporolithon sp.

Highlights

• Intensive mariculture activities contribute to coastal acidification.

• Inorganic carbon use of calcifying macroalgae is diverse and species-specific.

• Long term exposure to extreme low-pH lowers growth and calcification of Sporolithon sp.

Abstract

Fish farming in coastal areas has become an important source of food to support the world’s increasing population. However, intensive and unregulated mariculture activities have contributed to changing seawater carbonate chemistry through the production of high levels of respiratory CO2. This additional CO2, i.e. in addition to atmospheric inputs, intensifies the effects of global ocean acidification resulting in localized extreme low pH levels. Marine calcifying macroalgae are susceptible to such changes due to their CaCO3 skeleton. Their physiological response to CO2-driven acidification is dependent on their carbon physiology. In this study, we used the pH drift experiment to determine the capability of 9 calcifying macroalgae to use one or more inorganic carbon (Ci) species. From the 9 species, we selected the rhodolith Sporolithon sp. as a model organism to investigate the long-term effects of extreme low pH on the physiology and biochemistry of calcifying macroalgae. Samples were incubated under two pH treatments (pH 7.9 = ambient and pH 7.5 = extreme acidification) in a temperature-controlled (26 ± 0.02 °C) room provided with saturating light intensity (98.3 ± 2.50 μmol photons m-2 s-1). After the experimental treatment period (40 d), growth rate, calcification rate, nutrient uptake rate, organic content, skeletal CO3-2, pigments, and tissue C, N and P of Sporolithon samples were compared. The pH drift experiment revealed species-specific Ci use mechanisms, even between congenerics, among tropical calcifying macroalgae. Furthermore, long-term extreme low pH significantly reduced the growth rate, calcification rate and skeletal CO3-2 content by 79%, 66% and 18%, respectively. On the other hand, nutrient uptake rates, organic matter, pigments and tissue C, N and P were not affected by the low pH treatments. Our results suggest that the rhodolith Sporolithon sp. is susceptible to the negative effects of extreme low pH resulting from intensive mariculture-driven coastal acidification.

Continue reading ‘Inorganic carbon utilization of tropical calcifying macroalgae and the impacts of intensive mariculture-derived coastal acidification on the physiological performance of the rhodolith Sporolithon sp.’

Ocean acidification impacts on biomass and fatty acid composition of a post-bloom marine plankton community

A mesocosm approach was used to investigate the effects of ocean acidification (OA) on a natural plankton community in coastal waters off Norway by manipulating CO2 partial pressure ( pCO2). Eight enclosures were deployed in the Raunefjord near Bergen. Treatment levels were ambient (~320 µatm) and elevated pCO2 (~2000 µatm), each in 4 replicate enclosures. The experiment lasted for 53 d in May-June 2015. To assess impacts of OA on the plankton community, phytoplankton and protozooplankton biomass and total seston fatty acid content were analyzed. In both treatments, the plankton community was dominated by the dinoflagellate Ceratium longipes. In the elevated pCO2 treatment, however, biomass of this species as well as that of other dinoflagellates was strongly negatively affected. At the end of the experiment, total dinoflagellate biomass was 4-fold higher in the control group than under elevated pCO2 conditions. In a size comparison of C. longipes, cell size in the high pCO2 treatment was significantly larger. The ratio of polyunsaturated fatty acids to saturated fatty acids of seston decreased at high pCO2. In particular, the concentration of docosahexaenoic acid (C 22:6n3c), essential for development and reproduction of metazoans, was less than half at high pCO2 compared to ambient pCO2. Thus, elevated pCO2 led to a deterioration in the quality and quantity of food in a natural plankton community, with potential consequences for the transfer of matter and energy to higher trophic levels.

Continue reading ‘Ocean acidification impacts on biomass and fatty acid composition of a post-bloom marine plankton community’

Intestinal response to ocean acidification in the European sea bass (Dicentrarchus labrax)

Highlights

• High CO2 reduced specific growth rate in sea bass juveniles.

• High CO2 increased intestinal bicarbonate secretion in the anterior and mid intestine.

• High CO2 increased intestinal carbonate precipitates 4.4-fold.

• High CO2 increased intestinal expression for atp6v1b (V-ATPase β subunit), slc4a4, slc26a3, and slc26a6.

Abstract

The intestine of marine fishes contributes to the ocean carbon cycle producing carbonate aggregates as part of the osmoregulatory process. Therefore, this study aimed to evaluate physiological adjustments of European sea bass (Dicentrarchus labrax) intestine to a higher pCO2 environment likely in the near future (~1700 μatm). At the whole-body level, hypercapnia for 5 weeks resulted in fish having a significantly diminished specific growth rate, condition factor and hepatosomatic index. An increase in plasma osmolality and HCO3− concentration was detected, paralleled by decreased metabolites concentrations. In the intestine, high seawater pCO2 was without effect on ouabain-sensitive ATPase activities, while Bafilomycin A1-sensitive ATPase activity significantly decreased in the anterior intestine. Anterior and mid intestine were mounted in Ussing chambers in order to measure bioelectrical parameters and bicarbonate secretion by pH-Stat ex-vivo. Hypercapnia induced a 2.3 and 2.8-fold increase in bicarbonate secretion rates in the anterior and mid intestine, respectively. In the intestinal fluid, HCO3− concentration increased 2.2-fold, and carbonate precipitates showed a 4.4-fold increase in response to hypercapnia, paralleled by a >3-fold increase of drinking and a >2-fold increase of intestinal volume at any given time. At the molecular level, hypercapnia elicited higher intestinal mRNA expression levels for atp6v1b (V-ATPase B subunit), slc4a4, slc26a3, and slc26a6, both in the anterior and mid intestine. As a whole, our results show that the intestine of sea bass responds to high seawater pCO2, a response that comes at a cost at the whole-body level with an impact in the fish specific growth rate, condition factor, and hepatosomatic index.

Continue reading ‘Intestinal response to ocean acidification in the European sea bass (Dicentrarchus labrax)’

Interactive effects of increased temperature, elevated pCO2 and different nitrogen sources on the coccolithophore Gephyrocapsaoceanica

As a widespread phytoplankton species, the coccolithophore Gephyrocapsaoceanica has a significant impact on the global biogeochemical cycle through calcium carbonate precipitation and photosynthesis. As global change continues, marine phytoplankton will experience alterations in multiple parameters, including temperature, pH, CO2, and nitrogen sources, and the interactive effects of these variables should be examined to understand how marine organisms will respond to global change. Here, we show that the specific growth rate of G. oceanica is reduced by elevated CO2 (1000 μatm) in -grown cells, while it is increased by high CO2 in -grown ones. This difference was related to intracellular metabolic regulation, with decreased cellular particulate organic carbon and particulate organic nitrogen (PON) content in the and high CO2 condition compared to the low CO2 condition. In contrast, no significant difference was found between the high and low CO2 levels in cultures (p > 0.05). The temperature increase from 20°C to 25°C increased the PON production rate, and the enhancement was more prominent in cultures. Enhanced or inhibited particulate inorganic carbon production rate in cells supplied with relative to was observed, depending on the temperature and CO2 condition. These results suggest that a greater disruption of the organic carbon pump can be expected in response to the combined effects of increased / ratio, temperature, and CO2 level in the oceans of the future. Additional experiments conducted under nutrient limitation conditions are needed before we can extrapolate our findings to the global oceans.

Continue reading ‘Interactive effects of increased temperature, elevated pCO2 and different nitrogen sources on the coccolithophore Gephyrocapsaoceanica’

Growth, biochemical, antioxidants, metabolic enzymes and hemocytes population of the shrimp Litopenaeus vannamei exposed to acidified seawater

Highlights

• CO2 driven ocean acidification (CDOA) might inhibit the growth of L. vannamei.

• CDOA will inhibit the biochemical, chitin and minerals in L. vannamei.

• CDOA will produce oxidative and metabolic stress in L. vannamei.

• CDOA can reduce the hemocytes level in L. vannamei.

Abstract

Acidification in the marine environment has become a global issue that creates serious threats to marine organisms. In the present study, we evaluated the effect of CO2 driven acidification on the shrimp Litopenaeus vannamei post-larvae (PL). L. vannamei PL were exposed to six different CO2 driven acidified seawater, such as pH 8.20 (control), pH 7.8 (IPCC-predicted ocean pH by 2100), 7.6, 7.4, 7.2 and 7.0 with corresponding pCO2 level of 380.66, 557.53, 878.55, 1355.48, 2129.46, and 3312.12 μatm for seven weeks. At the end of the acidification experiment, results revealed that survival, growth, feed index, biochemical constitutes, chitin, minerals (Na, K, and Ca), and hemocyte populations of shrimps were found to be significantly decreased in CO2 driven acidified seawater which indicates the negative impacts of acidified seawater on these parameters in L. vannamei. Further, the level of antioxidants, lipid peroxidation, and metabolic enzymes were significantly higher in the muscle of shrimps exposed to acidified seawater suggests that the L. vannamei under oxidative stress and metabolic stress. Among these various acidified seawater experiment, pH 7.6 to 7.0 produced a significantly adverse effect on shrimps. Hence, the present study concluded that the elevated level of seawater acidification can produce harmful effects on L. vannamei PL which leads to potential threats to shrimp species in the marine environment.

Continue reading ‘Growth, biochemical, antioxidants, metabolic enzymes and hemocytes population of the shrimp Litopenaeus vannamei exposed to acidified seawater’


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