Posts Tagged 'phanerogams'



Short term CO2 enrichment increases carbon sequestration of air-exposed intertidal communities of a coastal lagoon

In situ production responses of air-exposed intertidal communities under CO2 enrichment are reported here for the first time. We assessed the short-term effects of CO2 on the light responses of the net community production (NCP) and community respiration (CR) of intertidal Z. noltei and unvegetated sediment communities of Ria Formosa lagoon, when exposed to air. NCP and CR were measured in situ in summer and winter, under present and CO2 enriched conditions using benthic chambers. Within chamber CO2 evolution measurements were carried out by a series of short-term incubations (30 min) using an infra-red gas analyser. Liner regression models fitted to the NCP-irradiance responses were used to estimate the seasonal budgets of air-exposed, intertidal production as determined by the daily and seasonal variation of incident photosynthetic active radiation. High CO2 resulted in higher CO2 sequestration by both communities in both summer and winter seasons. Lower respiration rates of both communities under high CO2 further contributed to a potential negative climate feedback, except in winter when the CR of sediment community was higher. The light compensation points (LCP) (light intensity where production equals respiration) of Z. noltei and sediment communities also decreased under CO2 enriched conditions in both seasons. The seasonal community production of Z. noltei was 115.54 ± 7.58 g C m−2 season−1 in summer and 29.45 ± 4.04 g C m−2 season−1 in winter and of unvegetated sediment was 91.28 ± 6.32 g C m−2 season−1 in summer and 25.83 ± 4.01 g C m−2 season−1 in winter under CO2 enriched conditions. Future CO2 conditions may increase air-exposed seagrass production by about 1.5-fold and unvegetated sediments by about 1.2-fold.

Continue reading ‘Short term CO2 enrichment increases carbon sequestration of air-exposed intertidal communities of a coastal lagoon’

Short-term variability of carbon chemistry in two contrasting seagrass meadows at Dongsha Island: implications for pH buffering and CO2 sequestration

The diurnal cycles of carbon chemistry parameters, i.e., dissolved inorganic carbon (DIC), total alkalinity (TA), partial pressure of CO2 (pCO2), and pH, were investigated in two hydrodynamically contrasting seagrass meadows at Dongsha Island in the northern South China Sea in August 2015. The results show that the pH and TA were higher and that the pCO2 was lower in the semi-enclosed inner lagoon (IL) than on the open north shore (NS). The analyses of carbon chemistry parameters vs. dissolved oxygen and TA vs. DIC relationships reveal that the CO2 dynamics was dominated by photosynthesis/respiration (P/R) alone on the NS but by the combined effect of P/R and sedimentary anaerobic pathways in the IL. We suggest that the observed divergent behaviors in carbon chemistry between the two sites could be attributed to differences in hydrodynamic regimes. The less energetic hydrodynamics and longer residence time in the IL would be favorable for the occurrence of sedimentary anaerobic TA generation and the subsequent TA accumulation in the overlying waters. The elevated TA may lead to a pH increase and a pCO2 decrease, thus providing a buffering effect against ocean acidification (OA) and enhancing atmospheric CO2 sequestration at local scales. The present results demonstrate that hydrodynamic regime may play an important role in regulating biogeochemical processes in seagrass meadows, and thereby modulating their capacities in OA buffering and CO2 uptaking.

Continue reading ‘Short-term variability of carbon chemistry in two contrasting seagrass meadows at Dongsha Island: implications for pH buffering and CO2 sequestration’

Losing a winner: thermal stress and local pressures outweigh the positive effects of ocean acidification for tropical seagrasses

  • Seagrasses are globally important coastal habitat‐forming species, yet it is unknown how seagrasses respond to the combined pressures of ocean acidification and warming of sea surface temperature.
  • We exposed three tropical species of seagrass (Cymodocea serrulata, Halodule uninervis, and Zostera muelleri) to increasing temperature (21, 25, 30, and 35°C) and pCO2 (401, 1014, and 1949 μatm) for 7 wk in mesocosms using a controlled factorial design. Shoot density and leaf extension rates were recorded, and plant productivity and respiration were measured at increasing light levels (photosynthesis–irradiance curves) using oxygen optodes.
  • Shoot density, growth, photosynthetic rates, and plant‐scale net productivity occurred at 25°C or 30°C under saturating light levels. High pCO2 enhanced maximum net productivity for Z. muelleri, but not in other species. Z. muelleri was the most thermally tolerant as it maintained positive net production to 35°C, yet for the other species there was a sharp decline in productivity, growth, and shoot density at 35°C, which was exacerbated by pCO2.
  • These results suggest that thermal stress will not be offset by ocean acidification during future extreme heat events and challenges the current hypothesis that tropical seagrass will be a ‘winner’ under future climate change conditions.

Continue reading ‘Losing a winner: thermal stress and local pressures outweigh the positive effects of ocean acidification for tropical seagrasses’

Primary producers may ameliorate impacts of daytime CO2 addition in a coastal marine ecosystem

Predicting the impacts of ocean acidification in coastal habitats is complicated by bio-physical feedbacks between organisms and carbonate chemistry. Daily changes in pH and other carbonate parameters in coastal ecosystems, associated with processes such as photosynthesis and respiration, often greatly exceed global mean predicted changes over the next century. We assessed the strength of these feedbacks under projected elevated CO2 levels by conducting a field experiment in 10 macrophyte-dominated tide pools on the coast of California, USA. We evaluated changes in carbonate parameters over time and found that under ambient conditions, daytime changes in pH, pCO2, net ecosystem calcification (NEC), and O2 concentrations were strongly related to rates of net community production (NCP). CO2 was added to pools during daytime low tides, which should have reduced pH and enhanced pCO2. However, photosynthesis rapidly reduced pCO2 and increased pH, so effects of CO2 addition were not apparent unless we accounted for seaweed and surfgrass abundances. In the absence of macrophytes, CO2 addition caused pH to decline by ∼0.6 units and pCO2 to increase by ∼487 µatm over 6 hr during the daytime low tide. As macrophyte abundances increased, the impacts of CO2 addition declined because more CO2 was absorbed due to photosynthesis. Effects of CO2addition were, therefore, modified by feedbacks between NCP, pH, pCO2, and NEC. Our results underscore the potential importance of coastal macrophytes in ameliorating impacts of ocean acidification.

Continue reading ‘Primary producers may ameliorate impacts of daytime CO2 addition in a coastal marine ecosystem’

The response of seagrass (Posidonia oceanica) meadow metabolism to CO2 levels and hydrodynamic exchange determined with aquatic eddy covariance

We investigated light, water velocity, and CO2 as drivers of primary production in Mediterranean seagrass (Posidonia oceanica) meadows and neighboring bare sands using the aquatic eddy covariance technique. Study locations included an open-water meadow and a nearshore meadow, the nearshore meadow being exposed to greater hydrodynamic exchange. A third meadow was located at a CO2 vent. We found that, despite the oligotrophic environment, the meadows had a remarkably high metabolic activity, up to 20 times higher than the surrounding sands. They were strongly autotrophic, with net production half of gross primary production. Thus, P. oceanica meadows are oases of productivity in an unproductive environment. Secondly, we found that turbulent oxygen fluxes above the meadow can be significantly higher in the afternoon than in the morning at the same light levels. This hysteresis can be explained by the replenishment of nighttime-depleted oxygen within the meadow during the morning. Oxygen depletion and replenishment within the meadow do not contribute to turbulent O2 flux. The hysteresis disappeared when fluxes were corrected for the O2 storage within the meadow and, consequently, accurate metabolic rate measurements require measurements of meadow oxygen content. We further argue that oxygen-depleted waters in the meadow provide a source of CO2 and inorganic nutrients for fixation, especially in the morning. Contrary to expectation, meadow metabolic activity at the CO2 vent was lower than at the other sites, with negligible net primary production.

Continue reading ‘The response of seagrass (Posidonia oceanica) meadow metabolism to CO2 levels and hydrodynamic exchange determined with aquatic eddy covariance’

Global change effects on seagrass ecosystem

Rising carbon dioxide (CO2) concentrations in the atmosphere will increase the average pCO2 level in the world oceans, which will have a knock-on effect on the marine ecosystem. Coastal seagrass communities one of the most productive marine ecosystems are predicted to benefit from the increase in CO2 levels, but long-term effects of elevated CO2 on seagrass communities are less understood. Population reconstruction techniques was used to investigate the population dynamics of Cymodocea nodosa meadows, exposed to long term elevated CO2 at volcanic seeps off Greece and Italy. Effect of elevated CO2 was noticed on the growth, morphometry, density, biomass and age structure at CO2 seeps. Above to below ground biomass ratio of C. nodosa were higher at CO2 seeps than at reference sites. The plastochrome interval were similar at all CO2 seeps. The shoot age and shoot longevity of plants were lower at seeps than reference sites. The present recruitment (sampled year) of the seagrass were higher than long-term average recruitment of the communities near the seeps. Carbon to nitrogen ratios (%DW) of C. nodosa were higher in leaves at seeps. Annual leaf production was higher near the seeps. This study suggests increased production of C. nodosa under elevated CO2 levels, but other co-factors such as nutrients, trace metal toxicity must also be taken into consideration while predicting effects of future CO2 concentrations. Volcanic CO2 seeps are now being used as natural analogues for ocean acidification studies although these areas can be affected by trace element input and may alter ecosystem responses to gradient in carbonate chemistry. Here Fe and a range of trace elements (Cd, Co, Cu, Hg, Mn, Pb, Ni and Zn) were analysed from sediments and from the roots, rhizomes and leaves of seagrass at six CO2 seeps and reference sites off Greece and Italy. There were higher metal levels in sediment and seagrasses at all CO2 seeps than reference sites. Sediment Quality Guideline Quotient, a commonly used pollution index, indicated that some of the metals (Cd, Cu, Hg, Ni) were in high enough concentrations to have adverse biological effects, such as Cu at Ischia site and Hg at Vulcano. Higher accumulation of elements from sediments in roots and leaves at CO2 seeps were found from Bio Sediment Accumulation Factor index. There were higher levels of Cu, Fe, Mn and Zn in leaves and rhizomes for P. oceanica and higher levels of Cd, Co, Cu, Fe and Zn in C. nodosa compartments at CO2 seeps. Fe and Mn were found with positive correlation within sediment-roots and sediment-rhizomes, whereas Cd, Co and Pb were found with positive correlation in compartments of C. nodosa. In P. oceanica positive correlation were only observed for Cd within sediment-roots and plant compartments. Low pH and ocean acidification increased the concentration of elements at CO2 seeps than reference sites. Thus, caution is needed, when using volcanic seep systems as analogue for the effects of rising CO2, as metals can reach levels that are toxic to seagrass, masking any potential benefits of increased levels of carbon dioxide for seagrass productivity. Net community production (NCP) and community respiration (CR) were measured under air exposed and CO2 enriched conditions for intertidal Z. noltei meadows and unvegetated sediment communities during emersion in summer and winter seasons. Community production and respiration were measured in-situ using benthic chambers. CO2 flux under air and CO2 enriched conditions were measured over a series of short term incubations (30min) using an infra-red gas analyser. Incident photosynthetic active radiation (PAR) was recorded during the incubations covering the daily and seasonal variation. Linear regression model was used to test the effects of irradiance on net community production. NCP of Z. noltei community were higher under CO2 enriched conditions than air exposed conditions in both summer and winter seasons. There was no effect of CO2 on the CR rate of Z. noltei community in summer season. NCP of sediment community were higher in summer season and winter season under CO2 enriched conditions. Sediment CR rates were higher in winter than summer season. The light compensation point of Z. noltei and sediment community were lower in both seasons under CO2 enriched conditions. Seasonal budget of community production was higher in Z. noltei than sediment communities. A clear effect of PAR was noticed on the net community production of both communities. Higher PAR intensities resulted in higher NCP under CO2 enriched conditions for both communities. CO2 enrichment will have a positive effect on the intertidal communities during emersion.

Continue reading ‘Global change effects on seagrass ecosystem’

Reproductive trade-offs in a temperate reef fish under high pCO2 levels

Highlights

•Reproductive activity in two-spotted goby is stimulated under high  pCO2  levels.
•Females under high  pCO2  levels produce more eggs.
•Larvae of parental pairs under high  pCO2  levels hatch smaller.
•Different energy allocation strategies are used by females under .
•High  pCO2  levels.

Abstract

Fishes are currently facing novel types of anthropogenic stressors that have never experienced in their evolutionary history, such as ocean acidification. Under these stressful conditions, energetically costly processes, such as reproduction, may be sacrificed for increased chances of survival. This trade-off does not only affect the organism itself but may result in reduced offspring fitness. In the present study, the effects of exposure to high  pCO2 levels were tested on the reproductive performance of a temperate species, the two-spotted goby, Gobiusculus flavescens. Breeding pairs were kept under control (∼600 μatm, pH∼ 8.05) and high  pCO2  levels (∼2300 μatm, pH∼ 7.60) conditions for a 4-month period. Additionally, oxidative stress and energy metabolism-related biomarkers were measured. Results suggest that reproductive activity is stimulated under high  pCO2  levels. Parental pairs in the simulated ocean acidification conditions exhibited increased reproductive output, with 50% more clutches and 44% more eggs per clutch than pairs under control conditions. However, there was an apparent trade-off between offspring number and size, as larvae of parental pairs under high  pCO2  levels hatched significantly smaller, suggesting differences in parental provisioning, which could be related to the fact that these females produce more eggs. Moreover, results support the hypothesis of different energy allocation strategies used by females under high  pCO2  conditions. These changes might, ultimately, affect individual fitness and population replenishment.

Continue reading ‘Reproductive trade-offs in a temperate reef fish under high pCO2 levels’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,289,919 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book