Posts Tagged 'biological response'

Recoverable impacts of ocean acidification on the tubeworm, Hydroides elegans: implication for biofouling in future coastal oceans

Ocean uptake of anthropogenic CO2 causes ocean acidification (OA), which not only decreases the calcification rate, but also impairs the formation of calcareous shells or tubes in marine invertebrates such as the dominant biofouling tubeworm species, Hydroides elegans. This study examined the ability of tubeworms to resume normal tube calcification when returned to ambient pH 8.1 from a projected near-future OA level of pH 7.8. Tubeworms produced structurally impaired and mechanically weaker calcareous tubes at pH 7.8 compared to at pH 8.1, but were able to recover when the pH was restored to ambient levels. This suggests that tubeworms can physiologically recover from the impacts of OA on tube calcification, composition, density, hardness and stiffness when returned to optimal conditions. These results help understanding of the progression of biofouling communities dominated by tubeworms in future oceans with low pH induced by OA.

Continue reading ‘Recoverable impacts of ocean acidification on the tubeworm, Hydroides elegans: implication for biofouling in future coastal oceans’

CO2 and acid-base sensing

Carbon dioxide (CO2) and its hydration products hydrogen (H+), bicarbonate and carbonate ions collectively contribute to the acid-base status of aqueous solutions, and have major effects on the physiology of organisms. Correspondingly, organisms have developed the ability to sense specific acid-base disturbances that routinely arise from metabolic and environmental sources, and to coordinate a variety of homeostatic responses. A common requirement for all homeostatic mechanisms is the ability to sense specific acid-base disturbances and to coordinate appropriate responses. This chapter synthetizes our knowledge concerning the sensory pathways that allow fish to sense acid-base disturbances of both metabolic and environmental origin and the ensuing downstream physiological responses that promote homeostasis in different organs. We focus largely on the peripheral, and to a lesser extent, the central sites of CO2/H+ detection, emphasizing the cellular sites and molecular mechanisms of acid-base sensing.

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Effects of high CO2 on oxygen consumption rates, aerobic scope and swimming performance

An increased energetic cost of acid-base regulation in a high-CO2 environment has been predicted to affect key metabolic traits and performance in fish. This chapter examines the experimental evidence for the effect of elevated CO2 and low pH on minimum (resting) oxygen consumption rate (ṀO2min), critical oxygen level (O2crit), maximum oxygen consumption rate (ṀO2max), aerobic scope (AS; here defined as the absolute aerobic scope, i.e., the difference between ṀO2max and ṀO2min), and critical swimming speed (Ucrit), and discusses potential drivers of variability in the responses. Extreme increases in CO2 or pH tends to reduce ṀO2min, ṀO2max and Ucrit. The increases in CO2 expected from global climate change are minor from a physiological viewpoint, and many studies find no effect, while others find an increase in ṀO2min, and ṀO2max and AS can be unchanged or change in either direction. Routine oxygen consumption rate (ṀO2rout; the average oxygen consumption rate) is either unaffected or decreases, possibly influenced by changes in spontaneous activity, although changes in ṀO2min may drive the response as well. Because it is difficult to tease apart the causes of a change in ṀO2rout, unless activity and ṀO2min are both measured, ṀO2rout is not an appropriate measure for determining if there are added energetic costs of exposure to elevated CO2. There is a stronger relationship between ṀO2max and AS, than between AS and ṀO2min, and it cannot be assumed that AS will decrease if ṀO2min increases. The ecological implications of these variable and complex effects on traits related to aerobic metabolic rates are challenging to interpret. Since AS is unchanged in many cases, additional performance measures (e.g., behavior, growth, reproduction, survival) may be important, through non-oxygen limited mechanisms, when assessing the sensitivity of a given species to climate change relevant increases in CO2.

Continue reading ‘Effects of high CO2 on oxygen consumption rates, aerobic scope and swimming performance’

Acid-base physiology and CO2 homeostasis: regulation and compensation in response to elevated environmental CO2

Acid-base balance is one of the most tightly regulated physiological processes. Accumulation of metabolic CO2 produced at the tissues causes extra- or intracellular acidosis that can disrupt cellular processes. Consequently, fish have a well-developed system for CO2 transport and excretion; however, the system varies significantly among fish groups, which we review in this chapter. Elevated environmental CO2 that occurs naturally or due to anthropogenic factors (e.g., climate change and in aquaculture), in both freshwater and seawater, induces a rapid acid-base disturbance in fish. The resulting acidosis is compensated by a net elevation in plasma in exchange for [Cl−], primarily through processes at the gills, but also the kidney. The rate and completeness of acid-base compensation during CO2 exposure is affected by water ion composition, and at high CO2 levels, there appears to be an upper limit to the increase in plasma . Fish that naturally live in such high CO2 environments appear to have an exceptional capacity for intracellular pH regulation. While it has long been thought that fish would not be affected by climate change relevant CO2 levels, negative physiological effects are seen. The effect of fluctuating CO2 levels in both marine and freshwater environments may be especially problematic, and an area where more research is required.

Continue reading ‘Acid-base physiology and CO2 homeostasis: regulation and compensation in response to elevated environmental CO2’

The physiology of behavioral impacts of high CO2

Recent experimental studies show that relatively small increases in environmental CO2 can fundamentally alter the behavior of marine and freshwater fishes by altering and/or impairing the function of neurotransmitter receptors. Most evidence to date suggests that the underlying mechanism of these behavioral disruptions is linked to alterations of ion gradients across the GABAA receptor, responsible for inhibitory input in neural circuits throughout the nervous system. This chapter will describe the mechanism(s) through which acid-base compensation during exposure to high CO2 has downstream neurophysiological effects in fish, including new molecular evidence for a self-amplifying cycle in GABAergic neurotransmission during high CO2 exposure.

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Late Quaternary coccolith weight variations in the northern South China Sea and their environmental controls

Highlights

• High-resolution records of coccolith weights in the South China Sea.

• Different coccolithophore species show different variations in calcification.

•Coccolithophore calcification in nature is supposed to be affected by multiple factors.

Abstract

Coccolithophores are one of the most abundant and widespread groups of calcifying plankton and have attracted extensive study in terms of their likely response to ocean acidification. Conflicting results concerning coccolithophore calcification have been reported from both experimental and field studies. Due to their minute size, it is difficult to estimate the amount of calcite in coccoliths. Here we apply the SYRACO system to analyzing the weights and lengths of coccoliths produced by the dominant coccolithophore family Noëlaerhabdaceae. We obtain high-resolution coccolith weight and length records of GEO (Gephyrocapsa oceanica) and SPC (Emiliania huxleyi and small Gephyrocapsa spp.) groups from sediment core MD05-2904 in the northern South China Sea (SCS) over the past 200 kyr. A calcification index (CI) based on the coccolith weight and length is applied to evaluate the changes in coccolithophore calcification. The two groups of coccolith weights / CIs show different patterns on long term variations and during the last two terminations. We compare the coccolith weight and CI records with the environmental variables and carbonate chemistry parameters calculated in the same core. Our data reveals that sea surface temperature and insolation have weak correlations to coccolith weight and CI on long-term variations. The SPC weight / CI are correlated with the seawater pH and pCO2 variations while the GEO weight/ CI are more related to the nutrient variations. This imply a more significant role of ocean carbonate chemistry in the calcification of less calcified coccolithophores and nutrient concentration in the heavier calcifying coccolighophores.

Continue reading ‘Late Quaternary coccolith weight variations in the northern South China Sea and their environmental controls’

Elevated pCO2 does not impair performance in autotomised individuals of the intertidal predatory starfish Asterias rubens (Linnaeus, 1758)

Highlights

• Ocean acidification research requires further understanding on the interactions with other stressors.

• We examined the combined effects of pCO2 and arm autotomisation on Asterias rubens.

• Neither stressor affected mortality, growth, arm regeneration, righting time or arm calcium content.

• Lipid content in the pyloric caeca increased in response to elevated pCO2.

• A. rubens appears unaffected by short-term exposure to pCO2 levels predicted for 2100.

Abstract

The impacts of ocean acidification remain less well-studied in starfish compared to other echinoderm groups. This study examined the combined effects of elevated pCO2 and arm regeneration on the performance of the intertidal predatory starfish Asterias rubens, as both are predicted to come at a cost to the individual. A two-way factorial experiment (~400 μatm vs ~1000 μatm; autotomised vs non-automised individuals) was used to examine growth rates, lipid content (pyloric caeca and gonads), and calcium content (body wall) in both intact and regenerating arms, as well as subsequent effects on rate of arm regeneration, righting time (behaviour) and mortality over 120 days. Autotomised individuals tended to show lower (not significant), survival and growth. Elevated pCO2 had no effect on mortality, body growth, arm regeneration, righting time or arm calcium content. Lipid content was higher in the pyloric caeca, but not in the gonads, in response to elevated pCO2 irrespective of autotomisation. The results of the study suggest that adult A. rubens remain unaffected by increased pCO2 and/or arm autotomy for 120 days, although longer term experiments are necessary as the results indicated that survival, growth and calcification may be impaired with longer-term exposure to elevated pCO2.

Continue reading ‘Elevated pCO2 does not impair performance in autotomised individuals of the intertidal predatory starfish Asterias rubens (Linnaeus, 1758)’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book