Posts Tagged 'physiology'

Limits and patterns of acid-base regulation during elevated environmental CO2 in fish


• High aquatic CO2 may pose challenges to extra- and intra-cellular pH regulation in fish

• In this review we discuss the putative limits to extracellular pH regulation in fish and how some species use a strategy referred to as ‘preferential intracellular pH regulation’ to maintain pH homeostasis during exposure to CO2 tensions beyond their capacity for extracellular pH regulation.


Aquatic CO2 tensions may exceed 30–60 Torr (ca. 30,000–79,000 μatm, respectively; hypercarbia) in some environments inducing severe acid-base challenges in fish. Typically, during exposure to hypercarbia blood pH (pHe) is initially reduced and then compensated in association with an increase in plasma HCO3– in exchange for Cl−. Typically, intracellular pH (pHi) is reduced and recovery is to some degree coupled to pHe recovery (coupled pH regulation). However, during acute hypercarbia, pHe recovery has been proposed to be limited by an “apparent upper bicarbonate threshold”, restricting complete pHe recovery to below 15 Torr PCO2. At PCO2 values beyond that which fish can compensate pHe, some fish are able to fully protect pHi despite large sustained reductions in pHe (preferential pHi regulation) and can tolerate PCO2 > 45 Torr. This review discusses pHe and pHi regulation during exposure to hypercarbia starting with modeling the capacity and theoretical limit to pHe compensation in 19 studies. Next, we discuss how fish compensate severe acute hypercarbia exposures beyond the putative limit of pHe compensation using preferential pHi regulation which has recently been observed to be common among fish subjected to severe hypercarbia. Finally, we consider the evolution of pH regulatory strategies in vertebrates, including how the presence of preferential pHi regulation in embryonic reptiles may indicate that it is an embryonic trait that is either lost or retained in adult vertebrates and may have served as an exaptation for evolutionary transitions during vertebrate evolution.

Continue reading ‘Limits and patterns of acid-base regulation during elevated environmental CO2 in fish’

Ocean acidification has little effect on the biochemical composition of the coccolithophore Emiliania huxleyi

Owing to the hierarchical organization of biology, from genomes over transcriptomes and proteomes down to metabolomes, there is continuous debate about the extent to which data and interpretations derived from one level, e.g. the transcriptome, are in agreement with other levels, e.g. the metabolome. Here, we tested the effect of ocean acidification (OA; 400 vs. 1000 μatm CO2) and its modulation by light intensity (50 vs. 300 μmol photons m-2 s-1) on the biomass composition (represented by 75 key metabolites) of diploid and haploid life-cycle stages of the coccolithophore Emiliania huxleyi (RCC1216 and RCC1217) and compared these data with interpretations from previous physiological and gene expression screenings. The metabolite patterns showed minor responses to OA in both life-cycle stages. Whereas previous gene expression analyses suggested that the observed increased biomass buildup derived from lipid and carbohydrate storage, this dataset suggests that OA slightly increases overall biomass of cells, but does not significantly alter their metabolite composition. Generally, light was shown to be a more dominant driver of metabolite composition than OA, increasing the relative abundances of amino acids, mannitol and storage lipids, and shifting pigment contents to accommodate increased irradiance levels. The diploid stage was shown to contain vastly more osmolytes and mannitol than the haploid stage, which in turn had a higher relative content of amino acids, especially aromatic ones. Besides the differences between the investigated cell types and the general effects on biomass buildup, our analyses indicate that OA imposes only negligible effects on E. huxleyi´s biomass composition.

Continue reading ‘Ocean acidification has little effect on the biochemical composition of the coccolithophore Emiliania huxleyi’

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’

Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels

Elevated pCO2 and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of harmful algal blooms (HABs). Here, we tested whether empirical data support this hypothesis using a meta‐analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO2 and warming. Most of the available data on HAB responses towards the two tested climate change variables concern dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO2. Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO2 may present an additional competitive advantage for HAB species, particularly as CO2 was not shown to enhance growth rate of other non‐HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non‐HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions.

Continue reading ‘Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels’

How calorie-rich food could help marine calcifiers in a CO2-rich future

Increasing carbon emissions not only enrich oceans with CO2 but also make them more acidic. This acidifying process has caused considerable concern because laboratory studies show that ocean acidification impairs calcification (or shell building) and survival of calcifiers by the end of this century. Whether this impairment in shell building also occurs in natural communities remains largely unexplored, but requires re-examination because of the recent counterintuitive finding that populations of calcifiers can be boosted by CO2 enrichment. Using natural CO2 vents, we found that ocean acidification resulted in the production of thicker, more crystalline and more mechanically resilient shells of a herbivorous gastropod, which was associated with the consumption of energy-enriched food (i.e. algae). This discovery suggests that boosted energy transfer may not only compensate for the energetic burden of ocean acidification but also enable calcifiers to build energetically costly shells that are robust to acidified conditions. We unlock a possible mechanism underlying the persistence of calcifiers in acidifying oceans.

Continue reading ‘How calorie-rich food could help marine calcifiers in a CO2-rich future’

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’

Continuous photoperiod of the Arctic summer stimulates the photosynthetic response of some marine macrophytes


• Long photoperiods increase the photosynthetic activity of certain subarctic macrophytes.

• Increased CO2 had no effect on tested macrophytes.

• Highest increases of photosynthetic activity of A. nodosum and Z. marina at long day lengths; smaller increase for F. vesiculosus.

• Subarctic macrophytes, expanding as sea ice retreats, will benefit from long summer days.


Subarctic macrophytes are predicted to expand in the Arctic as a result of on-going global climate change. This will expose them to 24 h of light during the Arctic summer while pCO2 levels are predicted to rise globally. Here, we tested the photosynthetic activity of two brown macroalgae (Ascophyllum nodosum, Fucus vesiculosus) and one seagrass (Zostera marina) from subarctic Greenland, measuring their relative maximum electron transport rate (rETRmax), photosynthetic efficiency (α) and saturating irradiance (Ik) after 3 days of incubation at different photoperiods (12:12 h, 15:09 h, 18:06 h, 21:03 h and 24:00 h, light:dark) with ambient values of pCO2 (200 ppm, characteristic of current subarctic surface waters) and increased pCO2 (400 and 1000 ppm). The photosynthetic parameters rETRmax and Ik increased significantly with longer photoperiods and increased, however insignificantly, with increased pCO2. Responses differed between species. A. nodosum and Z. marina showed the highest increase of rETRmax and Ik from 12 h to 24 h while the increase of F. vesiculosus was smaller. Our results suggest that as subarctic macrophytes expand in the Arctic in response to retracting sea ice, the long summer days will stimulate the productivity of the species tested here, while the effect of high-CO2 environment needs further research.

Continue reading ‘Continuous photoperiod of the Arctic summer stimulates the photosynthetic response of some marine macrophytes’

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Ocean acidification in the IPCC AR5 WG II

OUP book