Posts Tagged 'biological response'



Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)

Acidification, deoxygenation, and warming are escalating changes in coastal waters throughout the world ocean, with potentially severe consequences for marine life and ocean-based economies. To examine the influence of these oceanographic changes on a key biological process, we measured the effects of current and expected future conditions in the California Current Large Marine Ecosystem on the fertilization success of the red abalone (Haliotis rufescens). Laboratory experiments were used to assess abalone fertilization success during simultaneous exposure to various levels of seawater pH (gradient from 7.95 to 7.2), dissolved oxygen (DO) ($60 and 180 mm. kg SW) and temperature (9, 13, and 18 C). Fertilization success declined continuously with decreasing pH but dropped precipitously below a threshold near pH 7.55 in cool (9 C—upwelling) to average (13 C) seawater temperatures. Variation in DO had a negligible effect on fertilization. In contrast, warmer waters (18 C) often associated with El Nino Southern Oscillation conditions in central California acted antagonistically with decreasing pH, largely reducing the strong negative influence below the pH threshold. Experimental approaches that examine the interactive effects of multiple environmental drivers and also strive to characterize the functional response of organisms along gradients in environmental change are becoming increasingly important in advancing our understanding of the real-world consequences of changing ocean conditions.

Continue reading ‘Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)’

Physiological and biochemical analyses shed light on the response of Sargassum vulgare to ocean acidification at different time scales

Studies regarding macroalgal responses to ocean acidification (OA) are mostly limited to short-term experiments in controlled conditions, which hamper the possibility to scale up the observations to long-term effects in the natural environment. To gain a broader perspective, we utilized volcanic CO2 vents as a “natural laboratory” to study OA effects on Sargassum vulgare at different time scales. We measured photosynthetic rates, oxidative stress levels, antioxidant contents, antioxidant enzyme activities, and activities of oxidative metabolic enzymes in S. vulgare growing at a natural acidified site (pH 6.7) compared to samples from a site with current pH (pH 8.2), used as a control one. These variables were also tested in plants transplanted from the control to the acidified site and vice-versa. After short-term exposure, photosynthetic rates and energy metabolism were increased in S. vulgare together with oxidative damage. However, in natural populations under long-term conditions photosynthetic rates were similar, the activity of oxidative metabolic enzymes was maintained, and no sign of oxidative damages was observed. The differences in the response of the macroalga indicate that the natural population at the acidified site is adapted to live at the lowered pH. The results suggest that this macroalga can adopt biochemical and physiological strategies to grow in future acidified oceans.

Continue reading ‘Physiological and biochemical analyses shed light on the response of Sargassum vulgare to ocean acidification at different time scales’

Effects of ocean acidification on the physiological performance and carbon production of the Antarctic sea ice diatom Nitzschia sp. ICE-H

Ocean acidification (OA) resulting from increasing atmospheric CO2 strongly influences marine ecosystems, particularly in the polar ocean due to greater CO2 solubility. Here, we grew the Antarctic sea ice diatom Nitzschia sp. ICE-H in a semicontinuous culture under low (~ 400 ppm) and high (1000 ppm) CO2 levels. Elevated CO2 resulted in a stimulated physiological response including increased growth rates, chlorophyll a contents, and nitrogen and phosphorus uptake rates. Furthermore, high CO2 enhanced cellular particulate organic carbon production rates, indicating a greater shift from inorganic to organic carbon. However, the cultures grown in high CO2 conditions exhibited a decrease in both extracellular and intracellular carbonic anhydrase activity, suggesting that the carbon concentrating mechanisms of Nitzschia sp. ICE-H may be suppressed by elevated CO2. Our results revealed that OA would be beneficial to the survival of this sea ice diatom strain, with broad implications for global carbon cycles in the future ocean.

Continue reading ‘Effects of ocean acidification on the physiological performance and carbon production of the Antarctic sea ice diatom Nitzschia sp. ICE-H’

Elevated CO2 and associated seawater chemistry do not benefit a model diatom grown with increased availability of light

Elevated CO2 is leading to a decrease in pH in marine environments (ocean acidification [OA]), altering marine carbonate chemistry. OA can influence the metabolism of many marine organisms; however, no consensus has been reached on its effects on algal photosynthetic carbon fixation and primary production. Here, we found that when the diatom Phaeodactylum tricornutum was grown under different pCO2 levels, it showed different responses to elevated pCO2 levels under growth-limiting (20 µmol photons m-2 s-1, LL) compared with growth-saturating (200 µmol photons m-2 s-1, HL) light levels. With pCO2 increased up to 950 µatm, growth rates and primary productivity increased, but in the HL cells, these parameters decreased significantly at higher concentrations up to 5000 µatm, while no difference in growth was observed with pCO2 for the LL cells. Elevated CO2 concentrations reduced the size of the intracellular dissolved inorganic carbon (DIC) pool by 81% and 60% under the LL and HL levels, respectively, with the corresponding photosynthetic affinity for DIC decreasing by 48% and 55%. Little photoinhibition was observed across all treatments. These results suggest that the decreased growth rates under higher CO2 levels in the HL cells were most likely due to acid stress. Low energy demand of growth and energy saving from the down-regulation of the CO2 concentrating mechanisms (CCM) minimized the effects of acid stress on the growth of the LL cells. These findings imply that OA treatment, except for down-regulating CCM, caused stress on the diatom, reflected in diminished C assimilation and growth rates.

Continue reading ‘Elevated CO2 and associated seawater chemistry do not benefit a model diatom grown with increased availability of light’

Climate change and tropical sponges: The effect of elevated pCO₂ and temperature on the sponge holobiont

As atmospheric CO₂ concentrations rise, associated ocean warming (OW) and ocean acidification (OA) are predicted to cause declines in reef-building corals globally, shifting reefs from coral-dominated systems to those dominated by less sensitive species. Sponges are important structural and functional components of coral reef ecosystems, but despite increasing field-based evidence that sponges may be ‘winners’ in response to environmental degradation, our understanding of how they respond to the combined effects of OW and OA is limited. This PhD thesis explores the response of four abundant Great Barrier Reef species – the phototrophic Carteriospongia foliascens and Cymbastela coralliophila and the heterotrophic Stylissa flabelliformis and Rhopaloeides odorabile to OW and OA levels predicted for 2100, under two CO₂ Representative Concentration Pathways (RCPs). The overall aim of this research is to bridge gaps in our understanding of how these important coral reef organisms will respond to projected climate change, to begin to explore whether a sponge dominated state is a possible future trajectory for coral reefs.

To determine the tolerance of adult sponges to climate change, these four species were exposed to OW and OA in the Australian Institute of Marine Science’s (AIMS) National Sea Simulator (SeaSim) in a 3-month experimental study. The first data chapter explores the physiological responses of these sponges to OW and OA to gain a broad understanding of sponge holobiont survival and functioning under these conditions. In this chapter I also address the hypothesis that phototrophic and heterotrophic sponges will exhibit differential responses to climate change. In the second and third data chapters I explore the cellular lipid and fatty acid composition of sponges, and how these biochemical constituents vary with OW and OA. Lipids and fatty acids are not only vital energy stores, they form the major components of cell membranes, and the structure and composition of these biochemical constituents ultimately determines the integrity and physiological competency of a cell. Therefore through these analyses I aimed to determine how OW and OA affects the metabolic balance of sponges, and to understand mechanisms underpinning observed systemic sponge responses. Finally, to provide greater insight into the population level impacts of climate change on tropical sponges, in the last data chapter I explore the response of the phototrophic species Carteriospongia foliascens to OW/OA throughout its developmental stages.

I found that while sponges can generally tolerate climate change scenarios predicted under the RCP6.0 conditions for 2100 (30ºC/ pH 7.8), environmental projections for the end of this century under the RCP8.5 (31.5ºC/ pH 7.6) will have significant implications for their survival. Temperature effects were much stronger than OA effects for all species; however, phototrophic and heterotrophic species responded differently to OA. Elevated pCO₂ exacerbated temperature stress in heterotrophic sponges but somewhat ameliorated thermal stress in phototrophic species. Furthermore, sponges with siliceous spiculated skeletons resisted the RCP 8.5 conditions for longer than the aspiculate species. Biochemical analysis revealed that spiculated species also have greater cell membrane support features, which is likely to contribute to the observed stress tolerance. I also found that the additional energy available to phototrophic sponges under OA conditions may be used for investment into cell membrane support, providing protection against thermal stress. Finally, larval survival and settlement success of C. foliascens was unaffected by OW and OA treatments, and juvenile sponges exhibited greater tolerance than their adult counterparts, again with evidence that OA reduces OW stress for some of these life stages.

Based on the species studied here, this thesis confirms that sponges are better able to deal with OW and OA levels predicted for 2100 under RCP6.0, compared to many corals for which survival in a high CO₂ world requires OW to remain below 1.5°C. This suggests sponges may be future ‘winners’ on coral reefs under global climate change. However, if CO₂ atm concentrations reach levels predicted under RCP8.5, the prognosis for sponge survival by the end of this century changes as inter-species sponge tolerances to OW and OA differ. Under this projection it is likely we will also start to see a shift in sponge populations to those dominated by phototrophic sponges with siliceous spiculated skeletons. Overall, this thesis gives a holistic view of OW and OA impacts on tropical sponges and provides the basis from which to explore the potential for a sponge-coral regime shift in a high CO₂ world.

Continue reading ‘Climate change and tropical sponges: The effect of elevated pCO₂ and temperature on the sponge holobiont’

Ocean acidification in the Baltic Sea : implications for the bivalve Macoma balthica

The Baltic Sea is one of the most human-impacted sea areas in the world and its ecosystems are exposed to a variety of stressors of anthropogenic origin. Large changes in the environmental conditions, species and communities of the Baltic Sea are predicted to occur due to global climate change, but the extent and magnitude of the future changes are challenging to estimate due to the multiple stressors simultaneously impacting the system. As an additional threat, future ocean acidification will play a role in modifying the environmental conditions, and these CO2-induced changes are predicted to be fast in the Baltic Sea. This is especially of concern for the species-poor, but functionally essential benthic communities where key species such as bivalve Macoma balthica live at the limits of their tolerance range, and are already regularly disturbed by environmental stressors such as hypoxia. Currently, only very limited knowledge about the effects of future ocean acidification exists for this species.

The overall aim of my thesis was to develop an understanding of the effects of CO2 increase on the vulnerability of Baltic Sea key species, and how this is related to other effects of climate change, e.g. an increase in bottom-water hypoxia. Specifically, I investigated how different life stages of the infaunal bivalve M. balthica could be affected by future ocean acidification. Survival, growth, behaviour and physiological responses were assessed in a combination of laboratory and mesocosm experiments by exposing different life stages of M. balthica to different pH levels over different time periods depending on the life stage in question. While some life stage-based differences in vulnerability and survival were found, the results indicate that reduced pH has a negative effect on all life stages. In larval M. balthica, even a slight pH decrease was found to cause significant negative changes during that delicate life stage, both by slowing growth and by decreasing survival. Other observed impacts included delayed settling of the post-larvae and increasing energetic demand of adult bivalves.

The results suggest consistent negative effects at all life stages with potential major implications for the resilience of M. Balthica populations, which are currently under threat from a range of anthropogenic stressors such as increasing hypoxia. The kind of experimental studies conducted in this thesis are useful for pinpointing mechanisms, but they are always simplifications of reality, however, and are usually conducted over time scales that are short in relation to the time scales over which ocean acidification is affecting populations, communities and ecosystems. To fully understand and to be able to estimate how the complex ecosystems are about to change in the future, incorporating more of the biotic interactions, impacting stressors and relevant environmental conditions are needed for increasing the level of realism in the experiments.

Continue reading ‘Ocean acidification in the Baltic Sea : implications for the bivalve Macoma balthica’

Deepwater carbonate ion concentrations in the western tropical Pacific since 250 ka: Evidence for oceanic carbon storage and global climate influence

We present new “size-normalized weight” (SNW)-Δ[CO32−] core-top calibrations for three planktonic foraminiferal species and assess their reliability as a paleo-alkalinity proxy. SNWs of Globigerina sacculifer and Neogloboquadrina dutertrei can be used to reconstruct past deep Pacific [CO32−], whereas SNWs of Pulleniatina obliquiloculata are controlled by additional environmental factors. Based on this methodological advance, we reconstruct SNW-based deepwater [CO32−] for core WP7 from the western tropical Pacific since 250 ka. Secular variation in the SNW proxy documents little change in deep Pacific [CO32−] between the Last Glacial Maximum and the Holocene. Further back in time, deepwater [CO32−] shows long-term increases from marine isotope stage (MIS) 5e to MIS 3 and from early MIS 7 to late MIS 6, consistent with the “coral reef hypothesis” that the deep Pacific Ocean carbonate system responded to declining shelf carbonate production during these two intervals. During deglaciations, we have evidence of [CO32−] peaks coincident with Terminations 2 and 3, which suggests that a breakdown of oceanic vertical stratification drove a net transfer of CO2 from the ocean to the atmosphere, causing spikes in carbonate preservation (i.e., the “deglacial ventilation hypothesis”). During MIS 4, a transient decline in SNW-based [CO32−], along with other reported [CO32−] and/or dissolution records, implies that increased deep-ocean carbon storage resulted in a global carbonate dissolution event. These findings provide new insights into the role of the deep Pacific in the global carbon cycle during the late Quaternary.

Continue reading ‘Deepwater carbonate ion concentrations in the western tropical Pacific since 250 ka: Evidence for oceanic carbon storage and global climate influence’


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Ocean acidification in the IPCC AR5 WG II

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