Posts Tagged 'physiology'

Dynamics of benthic metabolism, O2, and pCO2 in a temperate seagrass meadow

Seagrass meadows play an important role in “blue carbon” sequestration and storage, but their dynamic metabolism is not fully understood. In a dense Zostera marina meadow, we measured benthic O2 fluxes by aquatic eddy covariance, water column concentrations of O2, and partial pressures of CO2 (pCO2) over 21 full days during peak growing season in April and June. Seagrass metabolism, derived from the O2 flux, varied markedly between the 2 months as biomass accumulated and water temperature increased from 16°C to 28°C, triggering a twofold increase in respiration and a trophic shift of the seagrass meadow from being a carbon sink to a carbon source. Seagrass metabolism was the major driver of diurnal fluctuations in water column O2 concentration and pCO2, ranging from 173 to 377 μmol L−1 and 193 to 859 ppmv, respectively. This 4.5‐fold variation in pCO2 was observed despite buffering by the carbonate system. Hysteresis in diurnal water column pCO2 vs. O2 concentration was attributed to storage of O2 and CO2 in seagrass tissue, air–water exchange of O2 and CO2, and CO2 storage in surface sediment. There was a ~ 1:1 mol‐to‐mol stoichiometric relationship between diurnal fluctuations in concentrations of O2 and dissolved inorganic carbon. Our measurements showed no stimulation of photosynthesis at high CO2 and low O2 concentrations, even though CO2 reached levels used in IPCC ocean acidification scenarios. This field study does not support the notion that seagrass meadows may be “winners” in future oceans with elevated CO2 concentrations and more frequent temperature extremes.

Continue reading ‘Dynamics of benthic metabolism, O2, and pCO2 in a temperate seagrass meadow’

pH affects growth, physiology and agar properties of agarophyte Gracilaria changii (Rhodophyta) under low light intensity from Morib, Malaysia

• The highest and the lowest growth rates of G. changii was at pH 6.61 and pH 9.30, respectively.
• G. changii survived poorly under high pH with partial thallus degradation.
• Photosynthetic pigments and agar production were significantly affected by pH.


Changes in coastal water pH alter inorganic carbon chemistry and impose abiotic stress on photosynthetic marine organisms. The red algal cell wall contains sulfated agar which protects them against environmental stresses. In this study, we investigated the effects of three different pHs (6.61, 8.04 and 9.30) on Gracilaria changii cultured in artificial seawater for 3 and 6 days, respectively. The growth rate of G. changii was the highest and the lowest at pH 6.61 and pH 9.30, respectively. Partial thallus degradation was observed in seaweeds treated at pH 9.30. Upon a 3-day treatment, the levels of allophycocyanin, total phycobilins in G. changii cultured at pH 6.61, and all photosynthetic pigments in G. changii cultured at pH 9.30, were significantly lower than those cultured at pH 8.04. G. changii exposed to pH 9.30 for 6 days also had significantly lower levels of chlorophyll a and allophycocyanin than those treated at pH 8.04. A six-day treatment at pH 6.61 caused a decline in the content of chlorophyll a and carotenoids, but an increase in the levels of phycoerythrin, phycocyanin, and total phycobilins, compared to those treated at pH 8.04. G. changii samples treated at pH 6.61 and pH 9.30 have a higher agar content compared to those cultured at 8.04. Gel strength was significantly lower in seaweed cultured at pH 9.30, compared to those cultured at pH 8.04. Gelling temperature and 3,6-anhydrogalactose content of agar were significantly affected by different pHs, but no significant changes were found in the melting temperature, gel syneresis and sulfate content of agar upon treatments. These information enhance our knowledge on physiological response and agar production in G. changii at different pHs, and useful for optimization of seaweed cultivation system in future.

Continue reading ‘pH affects growth, physiology and agar properties of agarophyte Gracilaria changii (Rhodophyta) under low light intensity from Morib, Malaysia’

Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring

Coral calcification is expected to decline as atmospheric carbon dioxide concentration increases. We assessed the potential of Porites astreoides, Siderastrea siderea and Porites porites to survive and calcify under acidified conditions in a 2-year field transplant experiment around low pH, low aragonite saturation (Ωarag) submarine springs. Slow-growing S. siderea had the highest post-transplantation survival and showed increases in concentrations of Symbiodiniaceae, chlorophyll a and protein at the low Ωarag site. Nubbins of P. astreoides had 20% lower survival and higher chlorophyll a concentration at the low Ωarag site. Only 33% of P. porites nubbins survived at low Ωarag and their linear extension and calcification rates were reduced. The density of skeletons deposited after transplantation at the low Ωarag spring was 15–30% lower for all species. These results suggest that corals with slow calcification rates and high Symbiodiniaceae, chlorophyll a and protein concentrations may be less susceptible to ocean acidification, albeit with reduced skeletal density. We postulate that corals in the springs are responding to greater energy demands for overcoming larger differences in carbonate chemistry between the calcifying medium and the external environment. The differential mortality, growth rates and physiological changes may impact future coral species assemblages and the reef framework robustness.

Continue reading ‘Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring’

Marine mass mortality in a global change context: impacts on individuals, populations and communities

Human actions are pushing natural systems into states that have no historical precedent. In response, empirical and theoretical researchers are increasingly focused on developing ways to predict the responses of ecological systems to change. However, significant knowledge gaps remain, often leading to “ecological surprises” where observed impacts of global change do not align with existing theory or hypotheses. In this dissertation, I study the response to perturbations of a well-characterized system for ecological research, the Northeast Pacific rocky intertidal, to advance our understanding of and ability to predict the impacts of global change on individuals, populations and communities. In 2013 and 2014, sea star species along the west coast of North America were affected by an outbreak of Sea Star Wasting Syndrome (SSWS), resulting in an epidemic of mass mortality that spanned unprecedented geographic and temporal scales and resulted in the near extirpation of multiple sea star species from many locations along the coast. One of the species that was most strongly affected in the intertidal zone was Pisaster ochraceus, an iconic predatory sea star that has the ability to play a keystone role in its community through foraging on and ultimately controlling the lower boundary of mussel prey populations. The first two chapters of this dissertation take advantage of SSWS as a “natural” form of top predator removal to assess the consequences of this type of perturbation on ecosystem resilience. In Chapter 2, I tested the hypotheses that P. ochraceus loss would facilitate a population expansion of a smaller, mesopredator sea star, Leptasterias sp., and that this expansion would have negative effects on P. ochraceus population recovery. This result would follow expectations of competitive release and aligns with existing research on the competitive relationship between these species from the Northeast Pacific intertidal. I used field surveys to track Leptasterias populations just before the onset of and up to three years after SSWS. Contrary to expectation, I did not see an increase in the distribution or density of Leptasterias, and instead saw a decrease in individual size post-SSWS. Further, I found no evidence of competition between P. ochraceus recruits and Leptasterias for resources. Thus, although my hypotheses were grounded in theory and previous research, they were not supported by data. These results suggest that Leptasterias will not provide a bottleneck for P. ochraceus population recovery from SSWS, nor compensate for lowered P. ochraceus predation. The dynamics of P. ochraceus at the recruit (early benthic juvenile) life-history stage has long been considered a gap in our understanding of the species, as recruits have been historically rare in the intertidal and hard to study. Post-SSWS, however, many sites along the coast experienced unprecedented recruitment of P. ochraceus into intertidal ecosystems. In Chapter 3, I used a field experiment to test the hypothesis that this pulse of recruitment was facilitated by SSWS-related adult loss, the consequent decrease in predation by adult P. ochraceus, and increase in prey availability for recruits. Instead of finding evidence that adults dominate recruits in food competition and inhibit recruit success, I found that recruits have a negative effect on P. ochraceus adult densities. Further, treatments where recruits were excluded and only adults had access to prey communities showed the highest control of sessile invertebrate prey populations at the end of the year-long experiment. Thus, these results suggest that adult P. ochraceus will not hinder recruit recovery, but propose a mechanism whereby high recruit densities may increase vulnerability to SSWS-induced shifts in community structure. Outbreaks of mass mortality, particularly those as widespread as SSWS, are one of many ecological challenges driven by anthropogenic environmental changes such as warming and ocean acidification. However, predicting the vulnerability of species and populations to global change is an ongoing and significant challenge for researchers and managers. In Chapter 4 I assessed whether intraspecific physiological variability could help predict P. ochraceus recruit response to ocean acidification and warming. I found that individual metabolic rate interacted with ocean acidification and food availability to drive sea star growth, and that an interaction between metabolic rate and temperature also predicted sea star predation on Mytilus spp. mussels. Thus, these results have implications not only for P. ochraceus but also for its food web interactions. Incorporating these results into predictive frameworks may improve our ability to anticipate and scale up responses to global change across levels of ecological organization. In summary, my dissertation, although chock-full of surprises, presents several paths forward for improving predictive ability in the face of accelerating anthropogenic global changes. Further, we reinforce the notion that management strategies should be cautious and anticipate ecological surprises. Predicting the future is challenging even when predictions are well-informed, particularly in environmental contexts that have never been encountered before.

Continue reading ‘Marine mass mortality in a global change context: impacts on individuals, populations and communities’

Increased intestinal carbonate precipitate abundance in the sea bream (Sparus aurata L.) in response to ocean acidification

Marine fish contribute to the carbon cycle by producing mineralized intestinal precipitates generated as by-products of their osmoregulation. Here we aimed at characterizing the control of epithelial bicarbonate secretion and intestinal precipitate presence in the gilthead sea bream in response to predicted near future increases of environmental CO2. Our results demonstrate that hypercapnia (950 and 1800 μatm CO2) elicits higher intestine epithelial HCO3- secretion ex vivo and a subsequent parallel increase of intestinal precipitate presence in vivo when compared to present values (440 μatm CO2). Intestinal gene expression analysis in response to environmental hypercapnia revealed the up-regulation of transporters involved in the intestinal bicarbonate secretion cascade such as the basolateral sodium bicarbonate co-transporter slc4a4, and the apical anion transporters slc26a3 and slc26a6 of sea bream. In addition, other genes involved in intestinal ion uptake linked to water absorption such as the apical nkcc2 and aquaporin 1b expression, indicating that hypercapnia influences different levels of intestinal physiology. Taken together the current results are consistent with an intestinal physiological response leading to higher bicarbonate secretion in the intestine of the sea bream paralleled by increased luminal carbonate precipitate abundance and the main related transporters in response to ocean acidification.

Continue reading ‘Increased intestinal carbonate precipitate abundance in the sea bream (Sparus aurata L.) in response to ocean acidification’

Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish

Increased levels of dissolved carbon dioxide (CO2) drive ocean acidification and have been predicted to increase the energy use of marine fishes via physiological and behavioural mechanisms. This notion is based on a theoretical framework suggesting that detrimental effects on energy use are caused by plasma acid–base disruption in response to hypercapnic acidosis, potentially in combination with a malfunction of the gamma aminobutyric acid type A (GABAA) receptors in the brain. However, the existing empirical evidence testing these effects primarily stems from studies that exposed fish to elevated CO2 for a few days and measured a small number of traits. We investigated a range of energetic traits in juvenile spiny chromis damselfish (Acanthochromis polyacanthus) over 3 months of acclimation to projected end-of-century CO2 levels (~ 1000 µatm). Somatic growth and otolith size and shape were unaffected by the CO2 treatment across 3 months of development in comparison with control fish (~ 420 µatm). Swimming activity during behavioural assays was initially higher in the elevated CO2 group, but this effect dissipated within ~ 25 min following handling. The transient higher activity of fish under elevated CO2 was not associated with a detectable difference in the rate of oxygen uptake nor was it mediated by GABAA neurotransmitter interference because treatment with a GABAA antagonist (gabazine) did not abolish the CO2 treatment effect. These findings contrast with several short-term studies by suggesting that end-of-century levels of CO2 may have negligible direct effects on the energetics of at least some species of fish.

Continue reading ‘Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish’

Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2

• Climate Change (2300 scenario) has a significant impact on the acid-base status in H. americanus.

• Climate Change causes retention of ammonia in hemolymph.

• Under Climate Change conditions hemolymph pCO2 does NOT exceed environmental pCO2.

• Climate Change causes increase in MO2 and ammonia excretion.

• Climate Change causes decrease in citrate synthase in tail muscle.

The physiological consequences of exposing marine organisms to predicted future ocean scenarios, i.e. simultaneous increase in temperature and pCO2, have only recently begun to be investigated. Adult American lobster (Homarus americanus) were exposed to either current (16 °C, 47 Pa pCO2, pH 8.10) or predicted year 2300 (20 °C, 948 Pa pCO2, pH 7.10) ocean parameters for 14–16 days prior to assessing physiological changes in their hemolymph parameters as well as whole animal ammonia excretion and resting metabolic rate. Acclimation of lobster simultaneously to elevated pCO2 and temperature induced a prolonged respiratory acidosis that was only partially compensated for via accumulation of extracellular HCO3– and ammonia. Furthermore, acclimated animals possessed significantly higher ammonia excretion and oxygen consumption rates suggesting that future ocean scenarios may increase basal energetic demands on H. americanus. Enzyme activity related to protein metabolism (glutamine dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) in hepatopancreas and muscle tissue were unaltered in future ocean scenario exposed animals; however, muscular citrate synthase activity was reduced suggesting that, while protein catabolism may be unchanged, the net energetic output of muscle may be compromised in future scenarios. Overall, H. americanus acclimated to ocean conditions predicted for the year 2300 appear to be incapable of fully compensating against climate change-related acid-base challenges and experience an increase in metabolic waste excretion and oxygen consumption. Combining our study with past literature on H. americanus suggests that the whole lifecycle from larvae to adult stages is at risk of severe growth, survival and reproductive consequences due to climate change.

Continue reading ‘Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2’

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Ocean acidification in the IPCC AR5 WG II

OUP book