Posts Tagged 'Arctic'

Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species

Mitochondrial respiration is a multi-step pathway that involves matrix and membrane-associated enzymes and plays a key role in acclimation to variable environmental conditions, but until now it has not been clear which of these steps would be most important in acclimation to changing temperatures and CO2 levels. Considering scenarios of ocean warming and acidification we assessed the role and limitation to phenotypic plasticity in the hearts of two Gadoid species adapted to different thermal ranges: the polar cod (Boreogadus saida), an Arctic stenotherm, and the Northeast Arctic population of Atlantic cod (NEAC, Gadus morhua), a cold eurytherm. We analysed the capacity of single enzymes involved in mitochondrial respiration [citrate synthase (CS), succinate dehydrogenase (SDH), cytochrome c oxidase (CCO)], the capacity of the electron transport system and the lipid class composition of the cellular membranes. Juveniles of the two species were held for four months at four temperatures (0, 3, 6, 8 °C for polar cod and 3, 8, 12, 16 °C for NEAC), at both ambient and elevated PCO2 (400 µatm and 1170 µatm, respectively). Polar cod showed no changes in mitochondrial enzyme capacities and in the relative lipid class composition in response to altered temperature or elevated PCO2. The lack of cardiac cellular plasticity together with evidence at the whole-animal level coming from other studies is indicative of little or no ability to overcome stenothermy, in particular during acclimation to 8 °C. In contrast, eurythermal NEAC exhibited modifications of membrane composition towards a more rigid structure and altered enzyme capacities to preserve functionality at higher temperatures. Furthermore, in NEAC, the capacities of SDH, CCO and CS were increased by high levels of CO2 if combined with high temperatures (12 and 16 °C), suggesting the compensation of an inhibitory effect. These results indicate that the cold eurythermal species (NEAC) is able to alter its mitochondrial function to a far greater extent than the Arctic stenotherm (polar cod), indicating greater resilience to variable environmental conditions. This difference in plasticity may underpin differences in the resilience to climate change and affect future species distributions and, eventually, survival.

Continue reading ‘Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species’

Energy budget, growth and exercise as proxies for performance capacity and fitness in Arctic fishes

The boreal Atlantic cod (Gadus morhua) is entering the Arctic in response to rising water temperatures, likely increasing predation pressure on the endemic key species Polar cod (Boreogadus saida). In this thesis, I investigated the whole-animal performance of both fish species after long-term acclimation to future ocean acidification and warming conditions in order to estimate their future competitive strength. More precisely, I focused on aerobic performance such as baseline and maximum metabolism, as well as energetic investment into growth and swimming as indicators for fitness capacity under future ocean conditions. While G. morhua was thriving under conditions projected for the year 2100, the competitive strength of B. saida likely decreases. F.i., the growth performance of B. saida decreased at temperatures above 6 degree Celsius and the swimming performance was impaired under elevated PCO2 levels, potentially resulting in a higher vulnerability to predation and reduced foraging success.

Continue reading ‘Energy budget, growth and exercise as proxies for performance capacity and fitness in Arctic fishes’

In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat

Coral reef resilience depends on the balance between carbonate precipitation, leading to reef growth, and carbonate degradation, for example, through bioerosion. Changes in environmental conditions are likely to affect the two processes differently, thereby shifting the balance between reef growth and degradation. In cold-water corals estimates of accretion-erosion processes in their natural habitat are scarce and solely live coral growth rates were studied with regard to future environmental changes in the laboratory so far, limiting our ability to assess the potential of cold-water coral reef ecosystems to cope with environmental changes. In the present study, growth rates of the two predominant colour morphotypes of live Lophelia pertusa as well as bioerosion rates of dead coral framework were assessed in different environmental settings in Norwegian cold-water coral reefs in a 1-year in situ experiment. Net growth (in weight gain and linear extension) of live L. pertusa was in the lower range of previous estimates and did not significantly differ between inshore (fjord) and offshore (open shelf) habitats. However, slightly higher net growth rates were obtained inshore. Bioerosion rates were significantly higher on-reef in the fjord compared to off-reef deployments in- and offshore. Besides, on-reef coral fragments yielded a broader range of individual growth and bioerosion rates, indicating higher turnover in live reef structures than off-reef with regard to accretion-bioerosion processes. Moreover, if the higher variation in growth rates represents a greater variance in (genetic) adaptations to natural environmental variability in the fjord, inshore reefs could possibly benefit under future ocean change compared to offshore reefs. Although not significantly different due to high variances between replicates, growth rates of orange branches were consistently higher at all sites, while mortality was statistically significantly lower, potentially indicating higher stress-resistance than the less pigmented white phenotype. Comparing the here measured rates of net accretion of live corals (regardless of colour morphotype) with net erosion of dead coral framework gives a first estimate of the dimensions of both processes in natural cold-water coral habitats, indicating that calcium carbonate loss through bioerosion amounts to one fifth to one sixth of the production rates by coral calcification (disregarding accretion processes of other organisms and proportion of live and dead coral framework in a reef). With regard to likely accelerating bioerosion and diminishing growth rates of corals under ocean acidification, the balance of reef accretion and degradation may be shifted towards higher biogenic dissolution in the future.

Continue reading ‘In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat’

The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes

This study aims to perform the results of the investigation of the Kara Sea carbonate system changes and the factors that determine it. The important feature of the Kara Sea water structure is strong stratification caused mainly by the Ob’ and Yenisey rivers discharge which is estimated as 81% of the total continental runoff to the sea. Occurring climate changes, as an increase in the total volume of the Arctic Ocean water (due to melting of glaciers, sea ice decline and river runoff increase), air temperature and CO2 concentration growth should affect greatly the Kara Sea carbonate system. However, riverine water influence seems to be the main driver of future acidification of the Kara Sea water due to permafrost thawing as it stores a great amount of buried carbon. An increase of carbon (mainly inorganic) flow to the sea will lead to carbonate equilibrium shift, oxidation of organic matter and release of CO2 that ultimately leads to a decrease in pH and therefore acidification. The area of the riverine plume depends on the amount of freshwater flowing into the sea and the conditions of the wind forcing. According to the data from Shirshov Institute cruises within the plume area aragonite saturation is below 1 that shows its state as acidified. Prevalence of pCO2 values in the freshened surface layer over the atmospheric shows that atmospheric carbon dioxide, apparently, cannot serve as the main driver for the acidification of the surface waters of the Kara Sea. At the shallow shelf to the north of the Ob’ Inlet mouth we observe acidification of the whole water column from surface to the bottom layer due to elevated riverine discharge and increase of flowing terrestrial carbon.

Continue reading ‘The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes’

Net community production and carbon exchange from winter to summer in the Atlantic Water inflow to the Arctic Ocean

The eastern Fram Strait and area north of Svalbard, are influenced by the inflow of warm Atlantic water, which is high in nutrients and CO2, influencing the carbon flux into the Arctic Ocean. However, these estimates are mainly based on summer data and there is still doubt on the size of the net ocean Arctic CO2 sink. We use data on carbonate chemistry and nutrients from three cruises in 2014 in the CarbonBridge project (January, May, and August) and one in Fram Strait (August). We describe the seasonal variability and the major drivers explaining the inorganic carbon change (CDIC) in the upper 50 m, such as photosynthesis (CBIO), and air-sea CO2 exchange (CEXCH). Remotely sensed data describes the evolution of the bloom and net community production. The focus area encompasses the meltwater-influenced domain (MWD) along the ice edge, the Atlantic water inflow (AWD), and the West Spitsbergen shelf (SD). The CBIO total was 2.2 mol C m–2 in the MWD derived from the nitrate consumption between January and May. Between January and August, the CBIO was 3.0 mol C m–2 in the AWD, thus CBIO between May and August was 0.8 mol C m–2. The ocean in our study area mainly acted as a CO2 sink throughout the period. The mean CO2 sink varied between 0.1 and 2.1 mol C m–2 in the AWD in August. By the end of August, the AWD acted as a CO2 source of 0.7 mol C m–2, attributed to vertical mixing of CO2-rich waters and contribution from respiratory CO2 as net community production declined. The oceanic CO2 uptake (CEXCH) from the atmosphere had an impact on CDIC between 5 and 36%, which is of similar magnitude as the impact of the calcium carbonate (CaCO3, CCALC) dissolution of 6–18%. CCALC was attributed to be caused by a combination of the sea-ice ikaite dissolution and dissolution of advected CaCO3 shells from the south. Indications of denitrification were observed, associated with sea-ice meltwater and bottom shelf processes. CBIO played a major role (48–89%) for the impact on CDIC.

Continue reading ‘Net community production and carbon exchange from winter to summer in the Atlantic Water inflow to the Arctic Ocean’

Arctic sensitivity? Suitable habitat for benthic taxa is surprisingly robust to climate change

Arctic marine ecosystems are often assumed to be highly vulnerable to ongoing climate change, and are expected to undergo significant shifts in structure and function. Community shifts in benthic fauna are likely to result from changes in key physico-chemical drivers, such as ocean warming, but there is little ecological data on most Arctic species to support any specific predictions as to how vulnerable they are, or how future communities may be structured. We used a species distribution modeling approach (MaxEnt) to project changes over the 21st century in suitable habitat area for different species of benthic fauna by combining presence observations from the OBIS database with environmental data from a coupled climate-ocean model (SINMOD). Projected mean % habitat losses over taxonomic groups were small (0–11%), and no significant differences were found between Arctic, boreal, or Arcto-boreal groups, or between calcifying and non-calcifying groups. However, suitable habitat areas for 14 of 78 taxa were projected a change by over 20%, and several of these taxa are characteristic and/or habitat-forming fauna on some Arctic shelves, suggesting a potential for significant ecosystem impacts. These results highlight the weakness of general statements regarding vulnerability of taxa on biogeographic or presumed physiological grounds, and suggest that more basic biological data on Arctic taxa are needed for improved projections of ecosystem responses to climate change.

Continue reading ‘Arctic sensitivity? Suitable habitat for benthic taxa is surprisingly robust to climate change’

The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light

Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 μatm) and future (1000 μatm) pCO2 levels under a constant as well as dynamic light, simulating natural light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimise its photophysiology for effective light usage during both low and high light periods. This effective photoacclimation, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla was able maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, physiologically plastic M. pusilla may exhibit a robust positive response to future Arctic Ocean conditions.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light’


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Ocean acidification in the IPCC AR5 WG II

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