Posts Tagged 'performance'

The power struggle: assessing interacting global change stressors via experimental studies on sharks

Ocean warming and acidification act concurrently on marine ectotherms with the potential for detrimental, synergistic effects; yet, effects of these stressors remain understudied in large predatory fishes, including sharks. We tested for behavioural and physiological responses of blacktip reef shark (Carcharhinus melanopterus) neonates to climate change relevant changes in temperature (28 and 31 °C) and carbon dioxide partial pressures (pCO2; 650 and 1050 µatm) using a fully factorial design. Behavioural assays (lateralisation, activity level) were conducted upon 7–13 days of acclimation, and physiological assays (hypoxia tolerance, oxygen uptake rates, acid–base and haematological status) were conducted upon 14–17 days of acclimation. Haematocrit was higher in sharks acclimated to 31 °C than to 28 °C. Significant treatment effects were also detected for blood lactate and minimum oxygen uptake rate; although, these observations were not supported by adequate statistical power. Inter-individual variability was considerable for all measured traits, except for haematocrit. Moving forward, studies on similarly ‘hard-to-study’ species may account for large inter-individual variability by increasing replication, testing larger, yet ecologically relevant, differences in temperature and pCO2, and reducing measurement error. Robust experimental studies on elasmobranchs are critical to meaningfully assess the threat of global change stressors in these data-deficient species.

Continue reading ‘The power struggle: assessing interacting global change stressors via experimental studies on sharks’

DNA methylation changes in response to ocean acidification at the time of larval metamorphosis in the edible oyster, Crassostrea hongkongensis

Highlights

  • Low pH stress resulted in hyper- and hypo-methylated genes in the pediveliger larvae of the Hong Kong oyster
  • Differentially methylated loci were concentrated in the exon region within the gene bodies
  • High capability of oyster larvae to acclimate and adapt to low pH condition within single generation despite poor habitat selection for attachment
  • Differential methylation is associated to higher metamorphosis success rate and poor larval substratum selection under low pH stress.

Abstract

Unprecedented rate of increased CO2 level in the ocean and the subsequent changes in carbonate system including decreased pH, known as ocean acidification (OA), is predicted to disrupt not only the calcification process but also several other physiological and developmental processes in a variety of marine organisms, including edible oysters. Nonetheless, not all species are vulnerable to those OA threats, e.g. some species may be able to cope with OA stress using environmentally induced modifications on gene and protein expressions. For example, external environmental stressors including OA can influence the addition and removal of methyl groups through epigenetic modification (e.g. DNA methylation) process to turn gene expression “on or off” as part of a rapid adaptive mechanism to cope with OA. In this study, we tested the above hypothesis through testing the effect of OA, using decreased pH 7.4 as proxy, on DNA methylation pattern of an endemic and a commercially important estuary oyster species, Crassostrea hongkongensis at the time of larval habitat selection and metamorphosis. Larval growth rate did not differ between control pH 8.1 and treatment pH 7.4. The metamorphosis rate of the pediveliger larvae was higher at pH 7.4 than those in control pH 8.1, however over one-third of the larvae raised at pH 7.4 failed to attach on optimal substrate as defined by biofilm presence. During larval development, a total of 130 genes were differentially methylated across the two treatments. The differential methylation in the larval genes may have partially accounted for the higher metamorphosis success rate under decreased pH 7.4 but with poor substratum selection ability. Differentially methylated loci were concentrated in the exon regions and appear to be associated with cytoskeletal and signal transduction, oxidative stress, metabolic processes, and larval metamorphosis, which implies the high potential of C. hongkongensis larvae to acclimate and adapt through non-genetic ways to OA threats within a single generation.

Continue reading ‘DNA methylation changes in response to ocean acidification at the time of larval metamorphosis in the edible oyster, Crassostrea hongkongensis’

The combined effects of ocean acidification and warming on a habitat-forming shell-crushing predatory crab

Highlights

  • We measured and compared traits at the cellular and organismal levels
  • Ocean warming and acidification affected crabs’ traits
  • Ocean warming increased the HSP70 levels
  • Crabs’ pinching strength was reduced by ocean acidification
  • Crabs’ self-righting speed was reduced by ocean warming and acidification

Abstract

In mid rocky intertidal habitats the mussel Perumytilus purpurarus monopolizes the substratum to the detriment of many other species. However, the consumption of mussels by the shell-crushing crab Acanthocyclus hassleri creates within the mussel beds space and habitat for several other species. This crab uses its disproportionately large claw to crush its shelled prey and plays an important role in maintaining species biodiversity. This study evaluated the consequences of projected near-future ocean acidification (OA) and warming (OW) on traits of A. hassleri linked with their predatory performance. Individual A. hassleri were maintained for 10-16 weeks under contrasting pCO2 (~500 and 1400 μatm) and temperature (~15 and 20 °C) levels. We compared traits at the organismal (oxygen consumption rate, survival, calcification rate, feeding rates, crusher claw pinching strength, self-righting speed, sarcomere length of the crusher claw muscles) and cellular (nutritional status ATP provisioning capacity through citrate synthase activity, expression of HSP70) level. Survival, calcification rate and sarcomere length were not affected by OA and OW. However, OW increased significantly feeding and oxygen consumption. Pinching strength was reduced by OA; meanwhile self-righting was increased by OA and OW. At 20 °C, carbohydrate content was reduced significantly by OA. Regardless of temperature, a significant reduction in energy reserves in terms of protein content by OA was found. The ATP provisioning capacity was significantly affected by the interaction between temperature and pCO2 and was highest at 15 °C and present day pCO2 levels. The HSP70 levels of crabs exposed to OW were higher than in the control crabs. We conclude that OA and OW might affect the amount and size of prey consumed by this crab. Therefore, by reducing the crab feeding performance these stressors might pose limits on their role in generating microhabitat for other rocky intertidal species inhabiting within mussel beds.

Continue reading ‘The combined effects of ocean acidification and warming on a habitat-forming shell-crushing predatory crab’

Coral-macroalgal competition under ocean warming and acidification

Highlights

  • Study investigates a common coral-macroalgal interaction under a low end emission scenario.
  • Light calcification is negatively influenced by an interaction of macroalgal contact and scenario.
  • Protein content, zooxanthellae density and Chlorophyll a were enhanced under scenario conditions.
  • Negative impacts of macroalgae on corals were observed, but not enhanced by scenario conditions.
  • More research on the impacts of climate change on the dynamics of coral-algal interactions is needed.

Abstract

Competition between corals and macroalgae is frequently observed on reefs with the outcome of these interactions affecting the relative abundance of reef organisms and therefore reef health. Anthropogenic activities have resulted in increased atmospheric CO2 levels and a subsequent rise in ocean temperatures. In addition to increasing water temperature, elevated CO2 levels are leading to a decrease in oceanic pH (ocean acidification). These two changes have the potential to alter ecological processes within the oceans, including the outcome of competitive coral-macroalgal interactions. In our study, we explored the combined effect of temperature increase and ocean acidification on the competition between the coral Porites lobata and on the Great Barrier Reef abundant macroalga Chlorodesmis fastigiata. A temperature increase of +1 °C above present temperatures and CO2 increase of +85 ppm were used to simulate a low end emission scenario for the mid- to late 21st century, according to the Representative Concentration Pathway 2.6 (RCP2.6). Our results revealed that the net photosynthesis of P. lobata decreased when it was in contact with C. fastigiata under ambient conditions, and that dark respiration increased under RCP2.6 conditions. The Photosynthesis to Respiration (P:R) ratios of corals as they interacted with macroalgal competitors were not significantly different between scenarios. Dark calcification rates of corals under RCP2.6 conditions, however, were negative and significantly decreased compared to ambient conditions. Light calcification rates were negatively affected by the interaction of macroalgal contact in the RCP2.6 scenario, compared to algal mimics and to coral under ambient conditions. Chlorophyll a, and protein content increased in the RCP2.6 scenario, but were not influenced by contact with the macroalga. We conclude that the coral host was negatively affected by RCP2.6 conditions, whereas the productivity of its symbionts (zooxanthellae) was enhanced. While a negative effect of the macroalga (C. fastigiata) on the coral (P. lobata) was observed for the P:R ratio under control conditions, it was not enhanced under RCP2.6 conditions.

Continue reading ‘Coral-macroalgal competition under ocean warming and acidification’

Ideas and perspectives: when ocean acidification experiments are not the same, reproducibility is not tested

Can experimental studies on the impacts of ocean acidification be trusted? That question was raised in early 2020 when a high-profile paper failed to corroborate previously-observed impacts of high CO2 on the behavior of coral reef fish. New information on the methodologies used in the replicated studies now provides the explanation: the experimental conditions were substantially different. High sensitivity to test conditions is characteristic of ocean acidification research; such response variability shows that effects are complex, interacting with many other factors. Open-minded assessment of all research results, both negative and positive, remains the best way to develop process-based understanding of those responses. Whilst replication studies can provide valuable insights and challenges, they can unfortunately also be counter-productive to scientific advancement if carried out in a spirit of confrontation rather than collaboration.

Continue reading ‘Ideas and perspectives: when ocean acidification experiments are not the same, reproducibility is not tested’

Current and future trophic interactions in tropical shallow-reef lagoon habitats

Calcium carbonate (CaCO3) sediments are the dominant form of CaCO3 on coral reefs accumulating in lagoon and inter-reefal areas. Owing to their mineralogy and a range of physical parameters, tropical CaCO3 sediments are predicted to be more sensitive to dissolution driven by ocean acidification than the skeleton of living reef organisms. How this scales up to impact infaunal organisms, which are an important food source for higher trophic levels, and thereby ecosystem functioning, is not well explored. We combined seasonal field surveys in a shallow-reef lagoon ecosystem on the Great Barrier Reef, Australia, with stable isotope analyses and a tank-based experiment to examine the potential top-down influence of the deposit-feeding sea cucumber, Stichopus herrmanni, on this infaunal community under current and future ocean pH. Densities of surface-sediment meiofauna were lowest in winter and spring, with harpacticoid copepods (38%) and nematodes (27%) the dominant taxa. Stable isotope analyses showed that S. herrmanni had a top-down influence on meiofauna and microphytes with a distinct δ13C and δ15N trophic position that was homogenous across seasons and locations. Tanks that mimicked sandy shallow-reef lagoon habitats were used to examine the effects of ocean acidification (elevated pCO2) on this trophic interaction. We used outdoor control (sediment only) and experimental (sediment plus S. herrmanni) tanks maintained at present-day and near-future pCO2 (+ 570 µatm) for 24 days, which fluctuated with the diel pCO2 cycle. In sediment-only tanks, copepods were > twofold more abundant at elevated pCO2, with no negative effects documented for any meiofauna group. When included in the community, top-down control by S. herrmanni counteracted the positive effects of low pH on meiofaunal abundance. We highlight a novel perspective in coral reef trophodynamics between surface-sediment meiofauna and deposit-feeding sea cucumbers, and posit that community shifts may occur in shallow-reef lagoon habitats in a future ocean with implications for the functioning of coral reefs from the bottom up.

Continue reading ‘Current and future trophic interactions in tropical shallow-reef lagoon habitats’

Ocean freshening and acidification differentially influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica

Highlights

  • Glacial retreat induced by global warming can decrease salinity and pH of the Antarctic ocean.
  • The Antarctic amphipod Gondogeneia antarctica was exposed to low salinity (27 psu) and low pH (7.6) conditions.
  • Low salinity increased cannibalism and induced adjusted swimming.
  • Low pH increased mortality, impaired food detection and reduced daytime shelter use.
  • Ocean freshening and acidification act as independent stressors influencing behavior and physiology of Antarctic amphipods.

Abstract

The Western Antarctic Peninsula (WAP) has experienced rapid atmospheric and ocean warming over the past few decades and many marine-terminating glaciers have considerably retreated. Glacial retreat is accompanied by fresh meltwater intrusion, which may result in the freshening and acidification of coastal waters. Marian Cove (MC), on King George Island in the WAP, undergoes one of the highest rates of glacial retreat. Intertidal and shallow subtidal waters are likely more susceptible to these processes, and sensitive biological responses are expected from the organisms inhabiting this area. The gammarid amphipod Gondogeneia antarctica is one of the most abundant species in the shallow, nearshore Antarctic waters, and it occupies an essential ecological niche in the coastal marine WAP ecosystem. In this study, we tested the sensitivity of G. antarctica to lowered salinity and pH by meltwater intrusion following glacial retreat. We exposed G. antarctica to four different treatments combining two salinities (34 and 27 psu) and pH (8.0 and 7.6) levels for 26 days. Mortality, excluding cannibalized individuals, increased under low pH but decreased under low salinity conditions. Meanwhile, low salinity increased cannibalism, whereas low pH reduced food detection. Shelter use during the daytime decreased under each low salinity and pH condition, indicating that the two stressors act as disruptors of amphipod behavior. Under low salinity conditions, swimming increased during the daytime but decreased at night. Although interactions between low salinity and low pH were not observed during the experiment, the results suggest that each stressor, likely induced by glacial melting, causes altered behaviors in amphipods. These environmental factors may threaten population persistence in Marian Cove and possibly other similar glacial embayments.

Continue reading ‘Ocean freshening and acidification differentially influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica’

Effects of low pH and low salinity induced by meltwater inflow on the behavior and physical condition of the Antarctic limpet, Nacella concinna

Seawater acidification and freshening in the intertidal zone of Marian Cove, Antarctica, which occurs by the freshwater inflow from snow fields and glaciers, could affect the physiology and behavior of intertidal marine organisms. In this study, we exposed Antarctic limpets, Nacella concinna, to two different pH (8.00 and 7.55) and salinity (34.0 and 27.0 psu) levels and measured their righting ability after being flipped over, mortality, condition factor, and shell dissolution. During the 35-day exposure, there was no significant difference in behavior and mortality between different treatments. However, the condition factor was negatively affected by low salinity. Both low pH and low salinity negatively influenced shell formation by decreasing the aragonite saturation state (Ωarg) and enhancing shell dissolution. Our results suggest that, though limpets can tolerate short-term low pH and salinity conditions, intrusions of meltwater accompanied by the glacial retreat may act as a serious threat to the population of N. concinna.

Continue reading ‘Effects of low pH and low salinity induced by meltwater inflow on the behavior and physical condition of the Antarctic limpet, Nacella concinna’

Ocean acidification disrupts the orientation of postlarval Caribbean spiny lobsters

Anthropogenic inputs into coastal ecosystems are causing more frequent environmental fluctuations and reducing seawater pH. One such ecosystem is Florida Bay, an important nursery for the Caribbean spiny lobster, Panulirus argus. Although adult crustaceans are often resilient to reduced seawater pH, earlier ontogenetic stages can be physiologically limited in their tolerance to ocean acidification on shorter time scales. We used a Y-maze chamber to test whether reduced-pH seawater altered the orientation of spiny lobster pueruli toward chemical cues produced by Laurencia spp. macroalgae, a known settlement cue for the species. We tested the hypothesis that pueruli conditioned in reduced-pH seawater would be less responsive to Laurencia spp. chemical cues than pueruli in ambient-pH seawater by comparing the proportion of individuals that moved to the cue side of the chamber with the proportion that moved to the side with no cue. We also recorded the amount of time (sec) before a response was observed. Pueruli conditioned in reduced-pH seawater were less responsive and failed to select the Laurencia cue. Our results suggest that episodic acidification of coastal waters might limit the ability of pueruli to locate settlement habitats, increasing postsettlement mortality.

Continue reading ‘Ocean acidification disrupts the orientation of postlarval Caribbean spiny lobsters’

Reply to: Methods matter in repeating ocean acidification studies

Replying to P. L. Munday et al. Nature https://doi.org/10.1038/s41586-020-2803-x (2020)

Pioneering papers by Munday and colleagues1,2 have reported profound effects of end-of-century ocean acidification—simulated by experimentally elevated CO2 levels in seawater—on the behaviour of coral reef fishes, such as extreme attraction of prey species to the chemical cues of their predators. Later studies by the same group reported that a range of other behaviours of coral reef fishes, including swimming activity, behavioural lateralization, homing and different predator avoidance behaviours, were also impaired by ocean acidification3 and that predator-escape behaviours in a coral reef mollusc were also impaired through the same physiological mechanism reported for fishes (that is, through effects on ‘GABAA-like receptors’), which led to the idea that “elevated-CO2 could cause behavioural impairment in a broad suite of marine animals”4. In 2014, we initiated experiments to further explore the physiological mechanism(s) that impaired coral reef fish behaviour in elevated levels of CO2; however, we immediately ran into a problem: despite several attempts, and many improvements to the standard methodology used in this field, we were unable to observe an effect of ocean acidification on fish behaviour. Our initial goal changed from what was meant to be a series of original experiments into a three-year effort to transparently examine behavioural effects of ocean acidification in coral reef fishes5; the findings of our study are the basis for the accompanying Comment by Munday et al.6.

Continue reading ‘Reply to: Methods matter in repeating ocean acidification studies’


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