Posts Tagged 'temperature'



The effects of ocean acidification, warming and enhanced nutrients on a Wadden Sea community – examined with mesocosm experiments

Ocean acidification and global warming are known as two of the most crucial factors impacting marine ecosystems worldwide. While most investigations tested short-term impacts of single environmental drivers (e.g. temperature, salintiy) on single species, studies on the combined effect of multiple drivers on a multi-species assemblage in different seasons, which is much more realistic and relevant, are still scarce. Therefore, an experimental mesocosm facility was built to gain information on community changes under the impacts from multiple drivers. In three consecutive experiments, in spring, summer and autumn 2014, compartments of an intertidal macroalgae-mussel community from the Wadden Sea were incubated for 8 to 11 weeks within a large-scale mesocosm facility (Sylt Benthic Mesocosm). In the experiments four different treatments were applied: Ambient, nutrient enrichment (N; doubled natural summer nutrient concentration), warming in combination with acidification (OAW; ambient + 5°C and 1000ppm), and a combination of all three drivers (OAW+N). To find seasonal effects, we compared the responses of (OAW) to that of the ambient treatment in spring, summer and autumn. Carbon flows within the food web of the enclosed species assemblage were analysed by a holistic, static modelling approach (Ecological Network Analysis, ENA). The combined effects of ocean warming and acidification decreased the biomass of the main grazers and the macrophyte Fucus vesiculosus, while epiphytes massively increased due to an altered top-down control during summer. This creates a bottle neck within the energy flow between the first two trophic levels and let less energy pass to higher trophic levels. Enriched nutrients alone did not affect the system substantially, but especially grazers seem to benefit from enriched nutrient concentrations. The effects of climate change on the investigated Wadden Sea community strongly depends on the investigated season. In spring and autumn, OAW affected less or even promoted the system by increased energy flows between the trophic levels. In summer the opposite was found, with decreased energy flow, hampered top-down control and a reduced trophic efficiency, that could propagate through the whole food web and alter the structure and functioning of the investigated community. The Analysis ENA showed a lower relative ascendancy and the trend to an increasing flow diversity, as the result of a high number of multiple pathways between the system components. Theoretically, the resilience of the system shows a tendency to increase and the capability of withstanding external disturbances under OAW as compared to an unstressed system.

Continue reading ‘The effects of ocean acidification, warming and enhanced nutrients on a Wadden Sea community – examined with mesocosm experiments’

Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean

The Arctic Ocean has been experiencing rapid warming, which accelerates sea ice melt. Further, the increasing area and duration of sea ice-free conditions enhance ocean uptake of CO2. We conducted two shipboard experiments in September 2015 and 2016 to examine the effects of temperature, CO2, and salinity on phytoplankton dynamics to better understand the impacts of rapid environmental changes on the Arctic ecosystem. Two temperature conditions (control: <3 and 5°C above the control), two CO2 levels (control: ∼300 and 300/450 μatm above the control; i.e., 600/750 μatm), and two salinity conditions (control: 29 in 2015 and 27 in 2016, and 1.4 below the control) conditions were fully factorially manipulated in eight treatments. Higher temperatures enhanced almost all phytoplankton traits in both experiments in terms of chl-a, accessory pigments and diatom biomass. The diatom diversity index decreased due to the replacement of chain-forming Thalassiosira spp. by solitary Cylindrotheca closterium or Pseudo-nitzschia spp. under higher temperature and lower salinity in combination. Higher CO2 levels significantly increased the growth of small-sized phytoplankton (<10 μm) in both years. Decreased salinity had marginal effects but significantly increased the growth of small-sized phytoplankton under higher CO2 levels in terms of chl-a in 2015. Our results suggest that the smaller phytoplankton tend to dominate in the shelf edge region of the Chukchi Sea in the western Arctic Ocean under multiple environmental perturbations.

Continue reading ‘Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean’

Linking energy budget to physiological adaptation: how a calcifying gastropod adjusts or succumbs to ocean acidification and warming

Highlights

• Energetics and shell properties of gastropods were measured under future climate.

• Ocean warming increased the feeding rate and hence energy budget of gastropods.

• The boosted energy budget was linked to increased shell growth and shell strength.

• Ocean acidification caused these positive effects of warming to become negative.

• Energy budget determined the adjustability of shell building process in calcifiers.

Abstract

Accelerating CO2 emissions have driven physico-chemical changes in the world’s oceans, such as ocean acidification and warming. How marine organisms adjust or succumb to such environmental changes may be determined by their ability to balance energy intake against expenditure (i.e. energy budget) as energy supports physiological functions, including those with adaptive value. Here, we examined whether energy budget is a driver of physiological adaptability of marine calcifiers to the near-future ocean acidification and warming; i.e. how physiological energetics (respiration rate, feeding rate, energy assimilation and energy budget) relates to adjustments in shell growth and shell properties of a calcifying gastropod (Austrocochlea concamerata). We found that ocean warming boosted the energy budget of gastropods due to increased feeding rate, resulting in faster shell growth and greater shell strength (i.e. more mechanically resilient). When combined with ocean acidification, however, the gastropods had a substantial decrease in energy budget due to reduced feeding rate and energy assimilation, leading to the reduction in shell growth and shell strength. By linking energy budget to the adjustability of shell building, we revealed that energy availability is critical to determine the physiological adaptability of marine calcifiers to the changing oceanic climate.

Continue reading ‘Linking energy budget to physiological adaptation: how a calcifying gastropod adjusts or succumbs to ocean acidification and warming’

Transcriptomic response to decreased pH in adult, larval and juvenile red king crab, Paralithodes camtschaticus, and interactive effects of pH and temperature on juveniles

Ocean warming and acidification are expected to influence the biology of the ecologically and economically important red king crab, Paralithodes camtschaticus. We investigated transcriptome responses of adult, larval and juvenile red king crab to assess sensitivity to reduced pH and elevated temperature. In adults, gill tissue (but not heart or cuticle) responded to reduced pH by differentially regulating many genes involved in metabolic, membrane and cuticular processes, but not ionic or acid/base regulation. In larval crabs, we found little evidence for a strong transcriptomic response to pH, but did observe large differences in the transcriptomes of newly hatched and one-week old larvae. In juvenile crabs, we found that there was a strong transcriptomic response to temperature across all pH conditions, but that only extreme low pH caused transcriptomic shifts. Most of the genes in juveniles that were differentially expressed were for cuticular and calcification processes. While inferences regarding the specific biological responses associated with changes in gene expression are likely to change as resources for red king crab genomics enabled studies continue to improve (i.e. better assemblies and annotation), our inferences about general sensitivities to temperature and pH across the life stages of red king crab are robust and unlikely to shift. Overall, our data suggest that red king crab are more sensitive to warming than acidification, and that responses to acidification at the transcriptomic level occur at different levels of pH across life stages, with juveniles being less pH sensitive than adults.

Continue reading ‘Transcriptomic response to decreased pH in adult, larval and juvenile red king crab, Paralithodes camtschaticus, and interactive effects of pH and temperature on juveniles’

Response of coralline algae Porolithon onkodes to elevated seawater temperature and reduced pH

Coralline algae (CA), a type of primary calcifying producer presented in coastal ecosystems, are considered one of the highly sensitive organisms to marine environmental change. However, experimental studies on coralline algae responses to elevated seawater temperature and reduced pH have documented either contradictory or opposite results. In this study, we analysed the growth and physiological responses of coralline algae Porolithon onkodes to the elevated temperature (30.8°C) and reduced pH (7.8). The aim of this analysis was to observe the direct and combined effects, while elucidating the growth and photosynthesis in this response. It was demonstrated that the algae thallus growth rate and photosynthesis under elevated temperature were depressed by 21.5% and 14.9% respectively. High pCO2 enhanced the growth and photosynthesis of the thallus at ambient temperature, while they were deceased when both temperature and pCO2 were elevated. CA is among the most sensitive organisms to ocean acidification (OA) because of their precipitate high Mg-calcite. We hypothesize that coralline algae could increase their calcification rate in order to counteract the effects of moderate acidification, but offset by the effect of elevated temperature. Accordingly, our results also support the conclusion that global warming (GW) is a stronger threat to algal performance than OA. Our findings are also proposed that coralline algae may be more
resilient under OA than GW.

Continue reading ‘Response of coralline algae Porolithon onkodes to elevated seawater temperature and reduced pH’

Paradise lost: end‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

Despite recent efforts to curtail greenhouse gas emissions, current global emission trajectories are still following the business‐as‐usual RCP8.5 emission pathway. The resulting ocean warming and acidification have transformative impacts on coral reef ecosystems, detrimentally affecting coral physiology and health, and these impacts are predicted to worsen in the near future. In this study, we kept fragments of the symbiotic corals Acropora intermedia (thermally sensitive) and Porites lobata (thermally tolerant) for 7 weeks under an orthogonal design of predicted end‐of‐century RCP8.5 conditions for temperature and pCO2 (3.5 °C and 570 ppm above present‐day respectively) to unravel how temperature and acidification, individually or interactively, influence metabolic and physiological performance. Our results pinpoint thermal stress as the dominant driver of deteriorating health in both species because of its propensity to destabilize coral‐dinoflagellate symbiosis (bleaching). Acidification had no influence on metabolism but had a significant negative effect on skeleton growth, particularly when photosynthesis was absent such as in bleached corals or under dark conditions. Total loss of photosynthesis after bleaching caused an exhaustion of protein and lipid stores and collapse of calcification that ultimately led to A. intermedia mortality. Despite complete loss of symbionts from its tissue, P. lobata maintained small amounts of photosynthesis and experienced a weaker decline in lipid and protein reserves that presumably contributed to higher survival of this species. Our results indicate that ocean warming and acidification under business‐as‐usual CO2 emission scenarios will likely extirpate thermally‐sensitive coral species before the end of the century, while slowing the recovery of more thermally‐tolerant species from increasingly severe mass coral bleaching and mortality. This could ultimately lead to the gradual disappearance of tropical coral reefs globally, and a shift on surviving reefs to only the most resilient coral species.

Continue reading ‘Paradise lost: end‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals’

Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification

Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remain poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioural plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam’s feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most probably due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioural changes of key species.

Continue reading ‘Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,325,348 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book