Posts Tagged 'respiration'

Bacterial community responses during a possible CO2 leaking from sub-seabed storage in marine polluted sediments

Carbon capture and storage (CCS) is a viable option to reduce high concentrations of CO2 and mitigate their negative effects. This option has associated risks such as possible CO2 leakage from the storage sites. So far, negative effects deriving from a CO2 release have been reported for benthic macrofauna in both polluted and nonpolluted sediments. However, bacterial communities has no considered. In this work, risk assessment was carried out in order to evaluate the possible effects in a contaminated area considering bacterial responses (total number of cells, respiring activity, changes in the bacterial community composition and diversity). Four microcosms were placed into an integrated CO2 injection system with a non-pressurized chamber to simulate four different pH treatments (pH control 7.8, 7, 6.5 and 6). Results showed an impact on bacterial communities because of the CO2 treatment. Changes in respiring activity, community composition groups and diversity were found. This study highlights the use of respiring bacteria activity not only as bioindicator for environmental risk assessment and monitoring purposes but also as a bioindicador during a CO2 leakage event or CO2 enrichment process among all the responses studied.

Continue reading ‘Bacterial community responses during a possible CO2 leaking from sub-seabed storage in marine polluted sediments’

The combined effects of increased temperature and ocean acidification on the early life history stages of Caribbean coral and its implication for the recovery potential of Florida reefs

The early life history stages of coral are an essential component determining the recovery potential of coral reefs through sexual reproduction and recruitment. The pelagic larval phase is inherent in all coral species regardless of differing reproductive strategies and is the only time in coral life history where large scale movement is possible allowing for the repopulation of reef areas both within and outside the natal reef habitat. In the face of climate change, the larval dispersal and recruitment phase will take place in a warmer more acidic ocean if we continue on the path of unabated fossil fuel emissions. While much research has focused on how increased temperature or ocean acidification affect coral larvae independently, our understanding of how these factors interact to shape larval response is limited, especially in regards to Caribbean coral species.

To gain a better understanding of how the early life history stages of Caribbean coral may be affected by climate change, this dissertation investigates the effects of increased temperature (2.5 °C above historical averages in the Florida Keys) and carbon dioxide levels (900-1000 parts per million CO2) on corals from the Florida Reef tract by investigating the effects on larval metabolism, survivorship, settlement, and post-settlement growth and survival. Additionally, a coupled biophysical model was developed to determine the potential changes in connectivity that may result from the biological effects of increased temperature and ocean acidification on the larval phase. The larval respiratory response of three Caribbean coral species revealed Orbicella faveolata as the most environmentally responsive with significant increases in respiration after 1 day exposure to increased temperature (68% greater than control conditions) with a counteracting effect of ocean acidification significantly decreasing respiration. The changes in metabolism over time correlated with decreased time to competency under elevated temperature in O. faveolata larvae, resulting in a greater number of settlers (76% greater than control) and a relative increase in local retention and self-recruitment rates as revealed by the biophysical model (5 and 7% greater than control respectively). However, when increased temperature occurred in combination with elevated CO2 levels, respiration was not significantly increased relative to control conditions and development of competency is minimally impacted. This resulted in a smaller increase in settlers (13% greater than control) and no significant changes in connectivity patterns. The post-settlement phase was similarly impacted with counteracting effects of increased temperature and ocean acidification on recruit growth.

Overall, this dissertation reveals the potential for adaptation to increased temperature in at least one important coral species (Orbicella faveolata) that is greatly diminished when encountered in combination with ocean acidification. These results encourage the reduction of carbon emissions to give coral species the chance to adapt to elevated temperatures through the recruitment of more resilient individuals without the additional stress of ocean acidification.

Continue reading ‘The combined effects of increased temperature and ocean acidification on the early life history stages of Caribbean coral and its implication for the recovery potential of Florida reefs’

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’

The regulation of coralline algal physiology, an in-situ study of Corallina officinalis (Corallinales, Rhodophyta)

Calcified macroalgae are critical components of marine ecosystems worldwide, but face considerable threat both from climate change (increasing water temperatures) and ocean acidification (decreasing ocean pH and carbonate saturation). It is thus fundamental to constrain the relationships between key abiotic stressors and the physiological processes that govern coralline algal growth and survival. Here we characterize the complex relationships between the abiotic environment of rock pool habitats, and the physiology of the geniculate red coralline alga, Corallina officinalis (Corallinales, Rhodophyta). Paired assessment of irradiance, water temperature and carbonate chemistry, with C. officinalis net production (NP), respiration (R) and net calcification (NG) was performed in a south-west UK field site, at multiple temporal scales (seasonal, diurnal and tidal). Strong seasonality was observed in NP and night-time R, with a Pmax of 22.35 μmol DIC gDW−1 h−1, Ek of 300 μmol photons m−2 s−1 and R of 3.29 μmol DIC gDW−1 −1 determined across the complete annual cycle. NP showed a significant exponential relationship with irradiance (R2 = 0.67), although was temperature dependent given ambient irradiance > Ek for the majority of the annual cycle. Over tidal emersion periods, dynamics in NP highlighted the ability of C. officinalis to acquire inorganic carbon despite significant fluctuations in carbonate chemistry. Across all data, NG was highly predictable (R2 = 0.80) by irradiance, water temperature and carbonate chemistry, providing a NGmax of 3.94  μmol CaCO3 gDW−1 h−1, and Ek of 113 μmol photons m−2 s−1. Light-NG showed strong seasonality and significant coupling to NP (R2 = 0.65), as opposed to rock pool water carbonate saturation. In contrast, the direction of dark-NG (dissolution vs. precipitation) was strongly related to carbonate saturation, mimicking abiotic precipitation dynamics. Data demonstrated that C. officinalis is adapted to both long-term (seasonal) and short-term (tidal) variability in environmental stressors, although the balance between metabolic processes and the external environment may be significantly impacted by future climate change.

Continue reading ‘The regulation of coralline algal physiology, an in-situ study of Corallina officinalis (Corallinales, Rhodophyta)’

Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival

Diel fluctuations in dissolved oxygen (DO) and pH create hypoxic conditions that alter the quality of shallow estuarine nursery habitats for juvenile fishes. Understanding how different species in these environments mitigate stress associated with intermittent hypoxia through compensatory behaviors, such as aquatic surface respiration (ASR), is important in determining the effect of these stressors on estuarine ecosystems. Behavioral responses of Atlantic silversides (Menidia menidia), striped killifish (Fundulus majalis), mummichog (Fundulus heteroclitus), and juvenile striped bass (Morone saxatilis) were independently observed during exposure to two levels of diel-cycling DO (3–9 mg O2 l− 1 and 1–11 mg O2 l− 1) each tested with both the corresponding pH cycle (7.2–7.8 and 6.8–8.1, respectively) and static pH (7.5) under controlled laboratory conditions. In treatments in which DO declined to ~ 3 mg O2 l− 1, none of the species examined exhibited ASR behavior either with or without the associated pH decline. However, ASR was observed during both 4-hour and extended 16-hour exposure where DO declined to ~ 1.0–1.6 mg O2 l− 1 in M. menidia and both Fundulus species. M. saxatilis did not exhibit ASR and no mortalities occurred during 4-hour low DO/pH treatments or during 16 hour exposure to 1.5 mg O2 l− 1. During extended 16-hour treatments, DO thresholds for ASR were not found to be different between F. majalis and F. heteroclitus, but both differed significantly from M. menidia. Across both 4-hour and 16-hour treatments, the onset of ASR was observed in M. menidia at or near lethal levels (1.31–1.62 mg O2 l− 1). No evidence of a pH (pCO2) effect on ASR or survival was found in any species in response to naturally co-varying DO and pH swings, despite pH as low as 6.8 and high pCO2 levels of >~12,000 μatm. These results suggest that utilization of ASR is a species-specific response influenced by the magnitude and duration of hypoxic exposure. ASR may serve as a last-ditch strategy by M. menidia to prolong survival for minutes to hours, but function as a means for F. heteroclitus to mitigate or reduce negative effects of hypoxia on a scale of days to weeks, with F. majalis exhibiting an intermediate response.

Continue reading ‘Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival’

Symbiodinium mitigate the combined effects of hypoxia and acidification on a non-calcifying cnidarian

Anthropogenic nutrient inputs enhance microbial respiration within many coastal ecosystems, driving concurrent hypoxia and acidification. During photosynthesis, Symbiodinium spp., the microalgal endosymbionts of cnidarians and other marine phyla, produce O2 and assimilate CO2, and thus potentially mitigate the exposure of the host to these stresses. However, such a role for Symbiodinium remains untested for non-calcifying cnidarians. We therefore contrasted the fitness of symbiotic and aposymbiotic polyps of a model host jellyfish (Cassiopea sp.) under reduced O2 (~2.09mgL−1) and pH (~pH 7.63) scenarios in a full factorial experiment. Host fitness was characterised as asexual reproduction and their ability to regulate internal pH and Symbiodinium performance characterised by maximum photochemical efficiency, chla content, and cell density. Acidification alone resulted in 58% more asexual reproduction of symbiotic polyps than aposymbiotic polyps (and enhanced Symbiodinium cell density) suggesting Cassiopea sp. fitness was enhanced by CO2-stimulated Symbiodinium photosynthetic activity. Indeed, greater CO2 drawdown (elevated pH) was observed within host tissues of symbiotic polyps under acidification regardless of O2 conditions. Hypoxia alone produced 22% fewer polyps than ambient conditions regardless of acidification and symbiont status, suggesting Symbiodinium photosynthetic activity did not mitigate its effects. Combined hypoxia and acidification, however, produced similar numbers of symbiotic polyps compared with aposymbiotic kept under ambient conditions, demonstrating that the presence of Symbiodinium was key for mitigating the combined effects of hypoxia and acidification on asexual reproduction. We hypothesise that this mitigation occurred because of reduced photorespiration under elevated CO2 conditions where increased net O2 production ameliorates oxygen debt. We show that Symbiodinium play an important role in facilitating enhanced fitness of Cassiopea sp. polyps, and perhaps also other non-calcifying cnidarian hosts, to the ubiquitous effects of ocean acidification. Importantly we highlight that symbiotic, non-calcifying cnidarians may be particularly advantaged in productive coastal waters that are subject to simultaneous hypoxia and acidification.

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Ocean acidification in the IPCC AR5 WG II

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