Posts Tagged 'abundance'

Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages

Increasing atmospheric carbon dioxide and its dissolution in seawater have reduced ocean pH and carbonate ion concentrations, with potential implications on calcifying organisms. To assess the response of large Caribbean benthic foraminifera to low carbonate saturation conditions, we analyzed benthic foraminifers’ abundance and relative distribution in surface sediments in proximity to low-carbonate-saturation submarine springs and at adjacent control sites. Our results show that the total abundance of large benthic foraminifera was significantly lower at the low-pH submarine springs than at control sites, although responses were species specific. The relative abundance of high-magnesium, porcelaneous foraminifera was higher than that of hyaline foraminifera at the low-pH springs due to the abundant Archaias angulatus, a chlorophyte-bearing foraminifer, which secretes a large and robust test that is more resilient to dissolution at low-calcite saturation. The different assemblages found at the submarine springs indicate that calcareous symbiont-barren foraminifera are more sensitive to the effects of ocean acidification than agglutinated and symbiont-bearing foraminifera, suggesting that future ocean acidification will likely impact natural benthic foraminifera populations.

Continue reading ‘Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages’

Condition of pteropod shells near a volcanic CO2 vent region

Highlights

 • in situ shell dissolution and change in shell biomass were the predominant features observed in the live pteropods collected within and nearby CO2 vent regions.

• Low pteropod biomass shells (collected nearby the CO2 vents) were more fragile and therefore more prone to fracture than the more robust, high biomass shells (collected in the control stations).

• In the Gulf of Naples, intermittent shifts away from optimum Ωar values can significantly affect pteropod calcification despite waters remaining oversaturated.

Abstract

Natural gradients of pH in the ocean are useful analogues for studying the projected impacts of Ocean Acidification (OA) on marine ecosystems. Here we document the in situ impact of submarine CO2 volcanic emissions (CO2 vents) on live shelled-pteropods (planktonic gastropods) species Creseis conica in the Gulf of Naples (Tyrrhenian Sea, Mediterranean). Since the currents inside the Gulf will likely drive those pelagic calcifying organisms into and out of the CO2 vent zones, we assume that pteropods will be occasionally exposed to the vents during their life cycle. Shell degradation and biomass were investigated in the stations located within and nearby the CO2 vent emission in relation to the variability of sea water carbonate chemistry. A relative decrease in shell biomass (22%), increase in incidence of shell fractures (38%) and extent of dissolution were observed in Creseis conica collected in the Gulf of Naples compared to those from the Northern Tyrrhenian Sea (control stations). These results suggest that discontinuous but recurrent exposure to highly variable carbonate chemistry could consistently affect the characteristic of the pteropod shells.

Continue reading ‘Condition of pteropod shells near a volcanic CO2 vent region’

Effect of elevated pCO2 on trace gas production during an ocean acidification mesocosm experiment (update)

A mesocosm experiment was conducted in Wuyuan Bay (Xiamen), China, to investigate the effects of elevated pCO2 on the phytoplankton species Phaeodactylum tricornutum (P. tricornutum), Thalassiosira weissflogii (T. weissflogii) and Emiliania huxleyi (E. huxleyi) and their production ability of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), as well as four halocarbon compounds, bromodichloromethane (CHBrCl2), methyl bromide (CH3Br), dibromomethane (CH2Br2) and iodomethane (CH3I). Over a period of 5 weeks, P. tricornuntum outcompeted T. weissflogii and E. huxleyi, comprising more than 99% of the final biomass. During the logarithmic growth phase (phase I), mean DMS concentration in high pCO2 mesocosms (1000µatm) was 28% lower than that in low pCO2 mesocosms (400µatm). Elevated pCO2 led to a delay in DMSP-consuming bacteria concentrations attached to T. weissflogii and P. tricornutum and finally resulted in the delay of DMS concentration in the high pCO2 treatment. Unlike DMS, the elevated pCO2 did not affect DMSP production ability of T. weissflogii or P. tricornuntum throughout the 5-week culture. A positive relationship was detected between CH3I and T. weissflogii and P. tricornuntum during the experiment, and there was a 40% reduction in mean CH3I concentration in the high pCO2 mesocosms. CHBrCl2, CH3Br, and CH2Br2 concentrations did not increase with elevated chlorophyll a (Chl a) concentrations compared with DMS(P) and CH3I, and there were no major peaks both in the high pCO2 or low pCO2 mesocosms. In addition, no effect of elevated pCO2 was identified for any of the three bromocarbons.

Continue reading ‘Effect of elevated pCO2 on trace gas production during an ocean acidification mesocosm experiment (update)’

CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium

We established the relationship between gross photosynthetic O2 evolution and light-dependent O2 consumption in Trichodesmium erythraeum IMS101 acclimated to three targeted pCO2 concentrations (180 µmol mol-1 = low-CO2, 380 µmol mol-1 = mid-CO2 and 720 µmol mol-1 = high-CO2). We found that biomass (carbon) specific, light-saturated maximum net O2 evolution rates (PnC,max) and acclimated growth rates increased from low- to mid-CO2, but did not differ significantly between mid- and high-CO2. Dark respiration rates were five-times higher than required to maintain cellular metabolism, suggesting that respiration provides a substantial proportion of the ATP and reductant for N2 fixation. Oxygen uptake increased linearly with gross O2 evolution across light intensities ranging from darkness to 1100 µmol photons m-2 s-1. The slope of this relationship decreased with increasing CO2, which we attribute to the increased energetic cost of operating the carbon concentrating mechanism (CCM) at lower CO2 concentrations. Our results indicate that net photosynthesis and growth of T. erythraeum IMS101 would have been severely CO2 limited at the last glacial maximum, but that the direct effect of future increases of CO2 may only cause marginal increases in growth.

Continue reading ‘CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium’

Elevated CO2 has little influence on the bacterial communities associated with the pH-tolerant coral, massive Porites spp.

Ocean acidification (OA) as a result of increased anthropogenic CO2 input into the atmosphere carries consequences for all ocean life. Low pH can cause a shift in coral-associated microbial communities of pCO2-sensitive corals, however, it remains unknown whether the microbial community is also influenced in corals known to be more tolerant to high pCO2/low pH. This study profiles the bacterial communities associated with the tissues of the pCO2-tolerant coral, massive Porites spp., from two natural CO2 seep sites in Papua New Guinea. Amplicon sequencing of the hypervariable V3-V4 regions of the 16S rRNA gene revealed that microbial communities remained stable across CO2 seep sites (pH = 7.44–7.85) and adjacent control sites (ambient pH = 8.0–8.1). Microbial communities were more significantly influenced by reef location than pH, with the relative abundance of dominant microbial taxa differing between reefs. These results directly contrast with previous findings that increased CO2 has a strong effect on structuring microbial communities. The stable structure of microbial communities associated with the tissues of massive Porites spp. under high pCO2/low pH conditions confirms a high degree of tolerance by the whole Porites holobiont to OA, and suggest that pH tolerant corals such as Porites may dominate reef assemblages in an increasingly acidic ocean.

Continue reading ‘Elevated CO2 has little influence on the bacterial communities associated with the pH-tolerant coral, massive Porites spp.’

Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment

The structural framework provided by corals is crucial for reef ecosystem function and services, but high seawater temperatures can be detrimental to the calcification capacity of reef-building organisms. The Red Sea is very warm, but total alkalinity (TA) is naturally high and beneficial for reef accretion. To date, we know little about how such detrimental and beneficial abiotic factors affect each other and the balance between calcification and erosion on Red Sea coral reefs, i.e., overall reef growth, in this unique ocean basin. To provide estimates of present-day reef growth dynamics in the central Red Sea, we measured two metrics of reef growth, i.e., in situ net-accretion/-erosion rates (Gnet) determined by deployment of limestone blocks and ecosystem-scale carbonate budgets (Gbudget), along a cross-shelf gradient (25km, encompassing nearshore, midshore, and offshore reefs). Along this gradient, we assessed multiple abiotic (i.e., temperature, salinity, diurnal pH fluctuation, inorganic nutrients, and TA) and biotic (i.e., calcifier and epilithic bioeroder communities) variables. Both reef growth metrics revealed similar patterns from nearshore to offshore: net-erosive, neutral, and net-accretion states. The average cross-shelf Gbudget was 0.66kg CaCO3m−2yr−1, with the highest budget of 2.44kg CaCO3m−2yr−1 measured in the offshore reef. These data are comparable to the contemporary Gbudgets from the western Atlantic and Indian oceans, but lie well below optimal reef production (5–10kg CaCO3m−2yr−1) and below maxima recently recorded in remote high coral cover reef sites. However, the erosive forces observed in the Red Sea nearshore reef contributed less than observed elsewhere. A higher TA accompanied reef growth across the shelf gradient, whereas stronger diurnal pH fluctuations were associated with negative carbonate budgets. Noteworthy for this oligotrophic region was the positive effect of phosphate, which is a central micronutrient for reef building corals. While parrotfish contributed substantially to bioerosion, our dataset also highlights coralline algae as important local reef builders. Altogether, our study establishes a baseline for reef growth in the central Red Sea that should be useful in assessing trajectories of reef growth capacity under current and future ocean scenarios.

Continue reading ‘Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment’

Differential physiological responses of the coastal cyanobacterium Synechococcus sp. PCC7002 to elevated pCO2 at lag, exponential, and stationary growth phases

We studied the effects of expected end-of-the-century pCO2 (1000 ppm) on the photosynthetic performance of a coastal marine cyanobacterium Synechococcus sp. PCC7002 during the lag, exponential, and stationary growth phases. Elevated pCO2 significantly stimulated growth, and enhanced the maximum cell density during the stationary phase. Under ambient pCO2 conditions, the lag phase lasted for 6 days, while elevated pCO2 shortened the lag phase to two days and extended the exponential phase by four days. The elevated pCO2 increased photosynthesis levels during the lag and exponential phases, but reduced them during the stationary phase. Moreover, the elevated pCO2 reduced the saturated growth light (Ik) and increased the light utilization efficiency (α) during the exponential and stationary phases, and elevated the phycobilisome:chlorophyll a (Chl a) ratio. Furthermore, the elevated pCO2 reduced the particulate organic carbon (POC):Chl a and particulate organic nitrogen (PON):Chl a ratios during the lag and stationary phases, but enhanced them during the exponential phase. Overall, Synechococcus showed differential physiological responses to elevated pCO2 during different growth phases, thus providing insight into previous studies that focused on only the exponential phase, which may have biased the results relative to the effects of elevated pCO2 in ecology or aquaculture.

Continue reading ‘Differential physiological responses of the coastal cyanobacterium Synechococcus sp. PCC7002 to elevated pCO2 at lag, exponential, and stationary growth phases’


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Ocean acidification in the IPCC AR5 WG II

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