Posts Tagged 'biological response'

Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions

Rising atmospheric CO2 is acidifying the world’s oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ 3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 °C under night and daylight (200 µmol photons m−2 s−1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 ± 0.7 at ΩArag ~ 2 and 5.6 ± 0.4 mmol CaCO3 m−2 day−1 at ΩArag ~ 3–3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2 ≥ 920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification.

Continue reading ‘Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions’

Antarctic marine biodiversity: adaptations, environments and responses to change

Animals living in the Southern Ocean have evolved in a singular environment. It shares many of its attributes with the high Arctic, namely low, stable temperatures, the pervading effect of ice in its many forms and extreme seasonality of light and phytobiont productivity. Antarctica is, however, the most isolated continent on Earth and is the only one that lacks a continental shelf connection with another continent. This isolation, along with the many millions of years that these conditions have existed, has produced a fauna that is both diverse, with around 17,000 marine invertebrate species living there, and has the highest proportions of endemic species of any continent. The reasons for this are discussed. The isolation, history and unusual environmental conditions have resulted in the fauna producing a range and scale of adaptations to low temperature and seasonality that are unique. The best known such adaptations include channichthyid icefish that lack haemoglobin and transport oxygen around their bodies only in solution, or the absence, in some species, of what was only 20 years ago termed the universal heat shock response. Other adaptations include large size in some groups, a tendency to produce larger eggs than species at lower latitudes and very long gametogenic cycles, with egg development (vitellogenesis) taking 18–24 months in some species. The rates at which some cellular and physiological processes are conducted appear adapted to, or at least partially compensated for, low temperature such as microtubule assembly in cells, whereas other processes such as locomotion and metabolic rate are not compensated, and whole-animal growth, embryonic development, and limb regeneration in echinoderms proceed at rates even slower than would be predicted by the normal rules governing the effect of temperature on biological processes. This review describes the current state of knowledge on the biodiversity of the Southern Ocean fauna and on the majority of known ecophysiological adaptations of coldblooded marine species to Antarctic conditions. It further evaluates the impacts these adaptations have on capacities to resist, or respond to change in the environment, where resistance to raised temperatures seems poor, whereas exposure to acidified conditions to end-century levels has comparatively little impact

Continue reading ‘Antarctic marine biodiversity: adaptations, environments and responses to change’

Fish brain development in a changing ocean

Unravelling how marine species invest in brain tissues (or brain regions) matching the fitness-relevant cognitive demands dictated by a changing environment is a priority in climate change-related (ocean warming and acidification) research. Within this context, this dissertation aimed to assess the combined effects of ocean warming (Δ 4 °C) and acidification (Δ 700 μatm pCO2 and Δ 0.4 pH) in the brain development (brain/body mass ratio and brain macro-region growth) of several juvenile fish species from different climate regions. Namely: three species adapted to a more stable (tropical) environment (clown anemonefish Amphiprion ocellaris, orchid dottyback Pseudochromis fridmani and neon goby Elacatinus oceanops), and other three adapted to a less stable (more seasonal; temperate) environment (seabream Diplodus sargus, flatfish Solea senegalensis and meagre Argyrosomus regius). The results show that the temperate species used in this study are only affected by ocean acidification in both total brain and specific brain regions, while the used tropical species are affected by ocean acidification, ocean warming and also by the interaction of ocean warming and ocean acidification. In fact, both total brain and every brain-region except for Telencephalon are affected by future conditions of ocean warming and ocean acidification differently according to each species. The lack of responses to ocean warming by the temperate species is here attributed to the widespread latitudinal distribution of those species, and thus the adaptation to a wider temperature range than tropical species. Curiously, all the significant interactions between the two studied stressors are antagonistic interactions with a cross-tolerance mechanism, meaning that under those interactions, the brain weight is closer to control levels than under each of the stressors separately. Possible behavioural and ecological implications of those results are also discussed. Despite the distinct dichotomic pattern between temperate and tropical habitats, the results among fish species and specific brain macro-regions do not exhibit a subjacent pattern. These different results highlight the idea of species-specific phenotypic responses to these climate change-related stressors.

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A potential role for epigenetic processes in the acclimation response to elevated pCO2 in the model diatom Phaeodactylum tricornutum

Understanding of the molecular responses underpinning diatom responses to ocean acidification is fundamental for predicting how important primary producers will be shaped by the continuous rise in atmospheric CO2. In this study, we have analyzed global transcriptomic changes of the model diatom Phaeodactylum tricornutum following growth for 15 generations in elevated pCO2 by strand-specific RNA sequencing (ssRNA-seq). Our results indicate that no significant effects of elevated pCO2 and associated carbonate chemistry changes on the physiological performance of the cells were observed after 15 generations whereas the expression of genes encoding histones and other genes involved in chromatin structure were significantly down-regulated, while the expression of transposable elements (TEs) and genes encoding histone acetylation enzymes were significantly up-regulated. Furthermore, we identified a series of long non-protein coding RNAs (lncRNAs) specifically responsive to elevated pCO2, suggesting putative regulatory roles for these largely uncharacterized genome components. Taken together, our integrative analyses reveal that epigenetic elements such as TEs, histone modifications and lncRNAs may have important roles in the acclimation of diatoms to elevated pCO2 over short time scales and thus may influence longer term adaptive processes in response to progressive ocean acidification.

Continue reading ‘A potential role for epigenetic processes in the acclimation response to elevated pCO2 in the model diatom Phaeodactylum tricornutum’

Boron isotope systematics of cultured brachiopods: response to acidification, vital effects and implications for palaeo-pH reconstruction

CO2-induced ocean acidification and associated decrease of seawater carbonate saturation state contributed to multiple environmental crises in Earth’s history, and currently poses a major threat for marine calcifying organisms. Owing to their high abundance and good preservation in the Phanerozoic geological record, brachiopods present an advantageous taxon of marine calcifiers for palaeo-proxy applications as well as studies on biological mechanism to cope with environmental change. To investigate the geochemical and physiological responses of brachiopods to prolonged low-pH conditions we cultured Magellania venosa, Terebratella dorsata and Pajaudina atlantica under controlled experimental settings over a period of more than two years. Our experiments demonstrate that brachiopods form their calcite shells under strong biological control, which enables them to survive and grow under low-pH conditions and even in seawater strongly undersaturated with respect to calcite (pH = 7.35, Ωcal = 0.6). Using boron isotope (δ11B) systematics including MC-ICP-MS as well as SIMS analyses, validated against in vivo microelectrode measurements, we show that this resilience is achieved by strict regulation of the calcifying fluid pH between the epithelial mantle and the shell. We provide a culture-based δ11B−pH calibration, which as a result of the internal pH regulatory mechanisms deviates from the inorganic borate ion to pH relationship, but confirms a clear yet subtle pH dependency for brachiopods. At a micro-scale level, the incorporation of 11B appears to be principally driven by a physiological gradient across the shell, where the δ11B values of the innermost calcite record the internal calcifying fluid pH while the composition of the outermost layers is also influenced by seawater pH. These findings are of consequence to studies on biomineralisation processes, physiological adaptations as well as past climate reconstructions.

Continue reading ‘Boron isotope systematics of cultured brachiopods: response to acidification, vital effects and implications for palaeo-pH reconstruction’

Diurnally fluctuating pCO2 modifies the physiological responses of coral recruits under ocean acidification

Diurnal pCO2 fluctuations have the potential to modulate the biological impact of ocean acidification (OA) on reef calcifiers, yet little is known about the physiological and biochemical responses of scleractinian corals to fluctuating carbonate chemistry under OA. Here, we exposed newly settled Pocillopora damicornis for 7 days to ambient pCO2, steady and elevated pCO2 (stable OA) and diurnally fluctuating pCO2 under future OA scenario (fluctuating OA). We measured the photo-physiology, growth (lateral growth, budding and calcification), oxidative stress and activities of carbonic anhydrase (CA), Ca-ATPase and Mg-ATPase. Results showed that while OA enhanced the photochemical performance of in hospite symbionts, it also increased catalase activity and lipid peroxidation. Furthermore, both OA treatments altered the activities of host and symbiont CA, suggesting functional changes in the uptake of dissolved inorganic carbon (DIC) for photosynthesis and calcification. Most importantly, only the fluctuating OA treatment resulted in a slight drop in calcification with concurrent up-regulation of Ca-ATPase and Mg-ATPase, implying increased energy expenditure on calcification. Consequently, asexual budding rates decreased by 50% under fluctuating OA. These results suggest that diel pCO2 oscillations could modify the physiological responses and potentially alter the energy budget of coral recruits under future OA, and that fluctuating OA is more energetically expensive for the maintenance of coral recruits than stable OA.

Continue reading ‘Diurnally fluctuating pCO2 modifies the physiological responses of coral recruits under ocean acidification’

Boron isotope composition of the cold-water coral Lophelia pertusa along the Norwegian margin: zooming into a potential pH-proxy by combining bulk and high-resolution approaches

High-latitude cold-water coral reefs are particularly vulnerable to climate change due to enhanced CO2 uptake in these regions. To evaluate their physiological functioning and potential application as pH archives, we retrieved both recent and fossil samples of Lophelia pertusa along the Norwegian margin from Oslofjord (59°N), over to Trondheimsfjord, Sula and Lopphavet (70.6°N). Boron isotope analyses (δ11B) were undertaken using solution-based and laser ablation multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS; LA-ICP-MS), and secondary ion mass spectrometry (SIMS). Epi-fluorescence microscopy was employed to provide a rapid pre-screening routine for structure-specific subsampling in the coral skeleton. This integrated approach enabled us to assess heterogeneities within single specimens, as well as to investigate the role of local environmental influences including recent and past variations. All three mass spectrometry methods show substantial differences in the δ11B of the theca wall (TW) and the centres of calcification (COC’s). Micro-bulk subsamples milled from the theca wall of modern specimens originating from different habitats but with comparable seawater pH (8–8.16) gave consistent δ11B values averaging 26.7 (±0.2‰, 2σ, n = 4), while COC subsamples systematically deviated towards lower B/Ca (by ~40%) and depleted δ11B values (minimum 22.7 ± 0.3‰, 2σ), implying a difference of at least 4‰ between TW and COC. SIMS and LA-ICP-MS measurements identified much larger internal heterogeneities with maximum variation of ~10‰ between the distinct skeletal structures; minimal SIMS δ11B values of ~17.3 ± 1.2‰ (2σ) were associated with the pure COC material. Our findings may be interpreted in terms of the occurrence of two main, but likely different, biomineralisation mechanisms in L. pertusa, with the COC’s generally exhibiting minimal pH up-regulation, potentially supporting the use of bicarbonate in the early stages of biomineralisation. Furthermore, we highlight the potential utility of L. pertusa for palaeo-proxy studies if targeting the compositionally homogenous TW zones devoid of COC admixtures, which appear to provide highly reproducible measurements.

Continue reading ‘Boron isotope composition of the cold-water coral Lophelia pertusa along the Norwegian margin: zooming into a potential pH-proxy by combining bulk and high-resolution approaches’


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Ocean acidification in the IPCC AR5 WG II

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