Posts Tagged 'performance'

Coastal pH variability and the eco-physiological and behavioural response of a coastal fish species in light of future ocean acidification

Ocean acidification (OA) is a global phenomenon referring to a decrease in ocean pH and a perturbation of the seawater carbonate system due to ever-increasing atmospheric CO2 concentrations. In coastal environments, identifying the impacts of OA is complex due to the multiple contributors to pH variability by coastal processes, such as freshwater inflow, upwelling, hydrodynamic processes, and biological activity. The aim of this PhD study was to quantify the local processes occurring in a temperate coastal embayment, Algoa Bay in South Africa, that contribute to pH and carbonate chemistry variability over time (monthly and 24-hour) and space (~10 km) and examine how this variability impacts a local fish species, Diplodus capensis, also commonly known as ‘blacktail’. Algoa Bay, known for its complex oceanography, is an interesting location in which to quantify carbonate chemistry variability. To assess this variability, monitoring sites were selected to coincide with the Algoa Bay Sentinel Site long-term ecological research (LTER) and continuous monitoring (CMP) programmes. The average pH at offshore sites in the bay was 8.03 ± 0.07 and at inshore sites was 8.04 ± 0.15. High pH variability (~0.55–0.61 pH units) was recorded at both offshore (>10 m depth) and inshore sites (intertidal surf zones). Many sites in the bay, especially the atypical site at Cape Recife, exhibit higher than the average pH levels (>8.04), suggesting that pH variability may be biologically driven. This is further evidenced by high diurnal variability in pH (~0.55 pH units). Although the specific drivers of the high pH variability in Algoa Bay could not be identified, baseline carbonate chemistry conditions were identified, which is necessary information to design and interpret biological experiments. Long-term, continuous monitoring is required to improve understanding of the drivers of pH variability in understudied coastal regions, like Algoa Bay.

Continue reading ‘Coastal pH variability and the eco-physiological and behavioural response of a coastal fish species in light of future ocean acidification’

Combined effects of ocean acidification and elevated temperature on feeding, growth, and physiological processes of Antarctic krill Euphausia superba

Antarctic krill Euphausia superba is a key species in the Southern Ocean, where its habitat is projected to undergo continued warming and increases in pCO2. Experiments during 2 summer field seasons at Palmer Station, Antarctica, investigated the independent and interactive effects of elevated temperature and pCO2 (decreased pH) on feeding, growth, acid-base physiology, metabolic rate, and survival of adult Antarctic krill. Ingestion and clearance rates of chlorophyll were depressed under low pH (7.7) compared to ambient pH (8.1) after a 48 h acclimation period, but this difference disappeared after a 21 d acclimation. Growth rates were negligible and frequently negative, but were significantly more negative at high (3°C, -0.03 mm d-1) compared to ambient temperature (0°C, -0.01 mm d-1) with no effect of pH. Modest elevations in tissue total CO2 and tissue pH were apparent at low pH but were short-lived. Metabolic rate increased with temperature but was suppressed at low pH in smaller but not larger krill. Although effects of elevated temperature and/or decreased pH were mostly sublethal, mortality was higher at high temperature/low pH (58%) compared to ambient temperature/pH or ambient temperature/low pH (>90%). This study identified 3 dominant patterns: (1) shorter-term effects were primarily pH-dependent; (2) krill compensated for lower pH relatively quickly; and (3) longer-term effects on krill growth and survival were strongly driven by temperature with little to no pH effect.

Continue reading ‘Combined effects of ocean acidification and elevated temperature on feeding, growth, and physiological processes of Antarctic krill Euphausia superba’

Cross‐generational response of a tropical sea urchin to global change and a selection event in a 43‐month mesocosm study

Long‐term experimental investigations of transgenerational plasticity (TGP) and transgenerational acclimatization to global change are sparse in marine invertebrates. Here, we test the effect of ocean warming and acidification over a 25‐month period of Echinometra sp. A sea urchins whose parents were acclimatized at ambient or one of two near‐future (projected mid‐ and end‐ of the 21st century) climate scenarios for 18 months. Several parameters linked to performance exhibited strong effects of future ocean conditions at 9 months of age. The Ambient‐Ambient group (A‐A, both F0 and F1 at ambient conditions) was significantly larger (21%) and faster in righting response (31%) compared to other groups. A second set of contrasts revealed near‐future scenarios caused significant negative parental carryover effects. Respiration at 9 months was depressed by 59% when parents were from near‐future climate conditions, and righting response was slowed by 28%. At ten months, a selective pathogenic mortality event lead to significantly higher survival rates of A‐A urchins. Differences in size and respiration measured prior to the mortality were absent after the event, while a negative parental effect on righting (29% reduction) remained. The capacity to spawn at the end of the experiment was higher in individuals with ambient parents (50%) compared to other groups (21%) suggesting persistent parental effects. Obtaining different results at different points in time illustrates the importance of longer‐term and multi‐generation studies to investigate effects of climate change. Given some animals in all groups survived the pathogenic event and that effects on physiology (but not behavior) among groups were eliminated after the mortality, we suggest that similar events could constitute selective sweeps, allowing genetic adaptation. However, given the observed negative parental effects and reduced potential for population replenishment it remains to be determined if selection would be sufficiently rapid to rescue this species from climate change effects.

Continue reading ‘Cross‐generational response of a tropical sea urchin to global change and a selection event in a 43‐month mesocosm study’

Elevated pCO2 reinforces preference among intertidal algae in both a specialist and generalist herbivore


  • Elevated pCO2 influences growth and chemical composition of some intertidal algae.
  • Herbivore preference is reinforced by resilience of preferred alga to pCO2 exposure.
  • Preference is also influenced by changes in lesser-preferred algal species.
  • Specialist and generalist feeding may be indirectly affected by ocean acidification.


Ocean acidification (OA) can induce changes in marine organisms and species interactions. We examined OA effects on intertidal macroalgal growth, palatability, and consumption by a specialist crab (Pugettia producta) and a generalist snail (Tegula funebralis) herbivore. Moderate increases in pCO2 increased algal growth in most species, but effects of pCO2 on C:N and phenolic content varied by species. Elevated pCO2 had no effect on algal acceptability to herbivores, but did affect their preference ranks. Under elevated pCO2, electivity for a preferred kelp (Egregia menziesii) and preference rankings among algal species strengthened for both P. producta and T. funebralis, attributable to resilience of E. menziesii in elevated pCO2 and to changes in palatability among less-preferred species. Preferred algae may therefore grow more under moderate pCO2 increases in the future, but their appeal to herbivores may be strengthened by associated shifts in nutritional quality and defensive compounds in other species.

Continue reading ‘Elevated pCO2 reinforces preference among intertidal algae in both a specialist and generalist herbivore’

Projected near-future ocean acidification decreases mercury toxicity in marine copepods


  • Copepods were subjected to OA and Hg pollution under multigenerational exposure.
  • OA reduced Hg accumulation and its toxicity to the growth/reproduction in copepods.
  • Copepod proteome enabled its physiological resilience to decreasing pH.
  • Proteomics indicated many toxic events, ensuring Hg toxicity to the copepod’s traits.
  • Proteome compensation was accounting for the alleviative effect of OA on Hg toxicity.


Here, we examined the combinational effect of ocean acidification (OA) and mercury (Hg) in the planktonic copepod Pseudodiaptomus annandalei in cross-factored response to different pCO2 (400, 800 μatm) and Hg (control, 1.0 and 2.5 μg/L) exposures for three generations (F0-F2), followed by single-generation recovery (F3) under clean condition. Several phenotypic traits and Hg accumulation were analyzed for F0-F3. Furthermore, shotgun-based quantitative proteomics was performed for F0 and F2. Our results showed that OA insignificantly influenced the traits. During F0-F2, combined exposure reduced Hg accumulation as compared with the counterpart Hg treatment, supporting the mitigating effect of OA on Hg toxicity in copepods. Proteomics analysis indicated that the copepods probably increased energy production/storage and stress response to ensure physiological resilience against OA. However, Hg induced many toxic events (e.g., energy depletion and degenerated organomorphogenesis/embryogenesis for F0; cell cycle arrest and detrimental stress-defense for F2), which were translated to the population-level adverse outcome, i.e., compromised growth/reproduction. Particularly, compensatory proteome response was identified (e.g., increased immune defense for F0; energetic compensation and enhanced embryogenesis for F2), accounting for a negative interaction between OA and Hg. Together, this study provides the molecular mechanisms behind the effects of OA and Hg pollution in marine copepods.

Continue reading ‘Projected near-future ocean acidification decreases mercury toxicity in marine copepods’

Effects of extra feeding combined with ocean acidification and increased temperature on the carbon isotope values (δ13C) in the mussel shell


  • Ocean acidification, OA, increased metabolic carbon uptake in mussel shell calcite.
  • Additive effects of increased temperature and extra feeding on carbon uptake.
  • Mussels alter their biomineralisation pathways relating to food carbon uptake.
  • Metabolic carbon uptake is 7–11% higher in the shell aragonite compared to calcite.
  • Molluscs with different composites may alter biomineralisation under OA.


Ocean acidification (OA) and global warming present future challenges for shell producing organisms such as mussels through reduction in the carbonate available to produce shells in these and other valuable aquaculture species. Molluscs control their shell growth through biomineralisation, but the response of the mechanisms behind biomineralisation to OA conditions are relatively unknown. It is unclear how much carbon is taken into the shell from the environment compared to the uptake through the food source. Shell production is energetically costly to molluscs and metabolic processes and energetic partitioning may affect their ability to perform the underlying mechanisms of biomineralisation under OA. It is possible that additional food consumption might alleviate some impacts caused by acidification. We assessed the ability of extra feeding to alter the impacts of OA and increased temperatures on adult Mytilus edulis. Carbon isotopes (δ13C) were used to examine the change in biomineralisation pathway in mussels. OA did not alter the δ13C directly in separate analyses of the shell calcite and aragonite layers, mantle tissue and extrapallial fluid. However, ambient treatments with increased temperatures altered the mussel biomineralisation pathway in the shell calcite using CO32− instead of HCO3 as the main source of carbon. The proportion of metabolic carbon uptake into the mussel shell calcite layer increased under OA, with additive effects when exposed to increased temperatures and extra feeding. The proportion of metabolic carbon uptake is higher (7%–11%) in the shell aragonite layer compared to calcite, under ambient treatments. OA initially reduced the metabolic carbon uptake into the shell aragonite, but after a period of 4-months with extra feeding, the mussels were able to adjust their metabolic carbon uptake to a level experienced under ambient treatments. This indicates that an abundance of food resources may enable changes in mussel biomineralisation pathways to compensate for any decrease in seawater inorganic carbon associated with OA. The impact of OA on phytoplankton varies from species to species, changing the structure of the community which could provide sufficient food resources to maintain metabolic carbon uptake for mussel shell growth. This study of δ13C isotopic values has identified changes in biomineralisation pathway relating to the mussel metabolic carbon uptake from their food source, with varying results for the aragonite and calcite shell polymorphs. The implications of these findings suggest that some bivalve species with different shell composites may cope better under OA than others, demanding further study into species-specific biomineralisation pathways.

Continue reading ‘Effects of extra feeding combined with ocean acidification and increased temperature on the carbon isotope values (δ13C) in the mussel shell’

Partner preference in the intertidal: possible benefits of ocean acidification to sea anemone-algal symbiosis

Ocean acidification (OA) threatens many marine species and is projected to become more severe over the next 50 years. Areas of the Salish Sea and Puget Sound that experience seasonal upwelling of low pH water are particularly susceptible to even lower pH conditions. While ocean acidification literature often describes negative impacts to calcifying organisms, including economically important shellfish, and zooplankton, not all marine species appear to be
threatened by OA. Photosynthesizing organisms, in particular, may benefit from increased levels of CO2. The aggregating anemone (Anthopleura elegantissima), a common intertidal organism throughout the northeast Pacific, hosts two photosynthetic symbionts: Symbiodinium muscatinei (a dinoflagellate) and Elliptochloris marina (a chlorophyte). The holobiont, therefore, consists of both a cnidarian host and a photosymbiont that could be affected differently by the changing levels of environmental CO2. To determine the effects of OA on this important marine organism, A. elegantissima in each of four symbiotic conditions (hosting S. muscatinei, hosting E. marina, hosting mixed symbiont assemblages, or symbiont free) were subjected to one of three pCO2 levels (800 ppm, 1200 ppm, or 1800 ppm) of OA for 10 weeks. At regular intervals, gross photosynthesis and density of the symbionts, respiration rate of the hosts, levels of reactive oxygen species (ROS) in the host, and percent of organic carbon received by the host from the symbiont (CZAR) were measured. Over the 10-week period of the experiment, the densities of symbionts responded differently to an increase in pCO2, increasing in anemones hosting S. muscatinei but decreasing for those hosting E. marina. Similarly, anemones of mixed symbiont complement that started with approximately 50% of each symbiont type shifted toward a higher percentage of S. muscatinei with higher pCO2. Both gross photosynthesis and dark respiration were significantly affected by pCO2 and symbiont state, though we cannot say that the symbiontsv responded differently to increased OA. Symbiont state was a significant predictor for ROS concentration, with greatest levels seen in anemones hosting E. marina and for CZAR score, with greatest levels in anemones hosting S. muscatinei, our linear models did not reveal pCO2 as a significant factor in these responses. Together, these results suggest that S. muscatinei may benefit from elevated pCO2 levels and that A. elegantissima hosting that symbiont may have a competitive advantage under some future scenarios of ocean acidification.

Continue reading ‘Partner preference in the intertidal: possible benefits of ocean acidification to sea anemone-algal symbiosis’

Ideas and perspectives: when ocean acidification experiments are not the same, repeatability is not tested (update)

Can experimental studies on the behavioural impacts of ocean acidification be trusted? That question was raised in early 2020 when a high-profile paper failed to corroborate previously observed responses of coral reef fish to high CO2. New information on the methodologies used in the “replicated” studies now provides a plausible 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. As in other fields, replication studies in ocean acidification are most likely to contribute to scientific advancement when carried out in a spirit of collaboration rather than confrontation.

Continue reading ‘Ideas and perspectives: when ocean acidification experiments are not the same, repeatability is not tested (update)’

Independent effects of seawater pH and high PCO2 on olfactory sensitivity in fish: possible role of carbonic anhydrase

Ocean acidification may alter olfactory-driven behaviour in fish by direct effects on the peripheral olfactory system; olfactory sensitivity is reduced in CO2-acidified seawater. The current study tested whether this is due to elevated PCO2 or the consequent reduction in seawater pH and, if the former, investigate the possible involvement of carbonic anhydrase, the enzyme responsible for the hydration of CO2 and production of carbonic acid. Olfactory sensitivity to amino acids was assessed by extracellular multi-unit recording from the olfactory nerve of the gilthead seabream (Sparus auratus L,) in normal seawater (pH ∼8.2), and after acute exposure to acidified seawater (pH ∼7.7, but normal PCO2; ∼340 µatm) and high PCO2 seawater (∼1400 µatm) at normal pH (∼8.2). Reduced pH in the absence of elevated PCO2 caused reduction in olfactory sensitivity to L-serine, L-leucine, L-arginine and L-glutamine, but not L-glutamic acid. Increased PCO2 in the absence of changes in pH caused reduced olfactory sensitivity to L-serine, L-leucine and L-arginine, including increases in their thresholds of detection, but had no effect on sensitivity to L-glutamine and L-glutamic acid. Inclusion of 1 mM acetazolamide (a membrane-permeant inhibitor of carbonic anhydrase) in the seawater reversed the inhibition of olfactory sensitivity to L-serine caused by high PCO2. Ocean acidification may reduce olfactory sensitivity by reduction in seawater pH and intracellular pH (of olfactory receptor neurones); the former by reducing odorant-receptor affinity, and the latter by reducing the efficiency of olfactory transduction. The physiological role of carbonic anhydrase in the olfactory receptor neurones remains to be explored.

Continue reading ‘Independent effects of seawater pH and high PCO2 on olfactory sensitivity in fish: possible role of carbonic anhydrase’

Effect of ocean acidification on bacterial metabolic activity and community composition in oligotrophic oceans, inferred from short-term bioassays

Increasing anthropogenic CO2 emissions in recent decades cause ocean acidification (OA), affecting carbon cycling in oceans by regulating eco-physiological processes of plankton. Heterotrophic bacteria play an important role in carbon cycling in oceans. However, the effect of OA on bacteria in oceans, especially in oligotrophic regions, was not well understood. In our study, the response of bacterial metabolic activity and community composition to OA was assessed by determining bacterial production, respiration, and community composition at the low-pCO2 (400 ppm) and high-pCO2 (800 ppm) treatments over the short term at two oligotrophic stations in the northern South China Sea. Bacterial production decreased significantly by 17.1–37.1 % in response to OA, since bacteria with high nucleic acid content preferentially were repressed by OA, which was less abundant under high-pCO2 treatment. Correspondingly, shifts in bacterial community composition occurred in response to OA, with a high fraction of the small-sized bacteria and high bacterial species diversity in a high-pCO2 scenario at K11. Bacterial respiration responded to OA differently at both stations, most likely attributed to different physiological responses of the bacterial community to OA. OA mitigated bacterial growth efficiency, and consequently, a larger fraction of DOC entering microbial loops was transferred to CO2.

Continue reading ‘Effect of ocean acidification on bacterial metabolic activity and community composition in oligotrophic oceans, inferred from short-term bioassays’

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Ocean acidification in the IPCC AR5 WG II

OUP book