Posts Tagged 'field'

Biomonitoring acidification using marine gastropods

Highlights

• Data loggers offer limited coverage of acidification in marine ecosystems.

• Intertidal water pH was reflected in organismal attributes of gastropods.

• Shell surface erosion presents a clear estimate of corrosive water exposure.

• Gastropod biomonitoring can identify coastal areas of more or lesser acidification.

Abstract

Ocean acidification is mainly being monitored using data loggers which currently offer limited coverage of marine ecosystems. Here, we trial the use of gastropod shells to monitor acidification on rocky shores. Animals living in areas with highly variable pH (8.6–5.9) were compared with those from sites with more stable pH (8.6–7.9). Differences in site pH were reflected in size, shape and erosion patterns in Nerita chamaeleon and Planaxis sulcatus. Shells from acidified sites were shorter, more globular and more eroded, with both of these species proving to be good biomonitors. After an assessment of baseline weathering, shell erosion can be used to indicate the level of exposure of organisms to corrosive water, providing a tool for biomonitoring acidification in heterogeneous intertidal systems. A shell erosion ranking system was found to clearly discriminate between acidified and reference sites. Being spatially-extensive, this approach can identify coastal areas of greater or lesser acidification. Cost-effective and simple shell erosion ranking is amenable to citizen science projects and could serve as an early-warning-signal for natural or anthropogenic acidification of coastal waters.

Continue reading ‘Biomonitoring acidification using marine gastropods’

Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species

Predictions of the effects of global change on ecological communities are largely based on single habitats. Yet in nature, habitats are interconnected through the exchange of energy and organisms, and the responses of local communities may not extend to emerging community networks (i.e. metacommunities). Using large mesocosms and meiofauna communities as a model system, we investigated the interactive effects of ocean warming and acidification on the structure of marine metacommunities from three shallow‐water habitats: sandy soft‐bottoms, marine vegetation and rocky reef substrates. Primary producers and detritus – key food sources for meiofauna – increased in biomass under the combined effect of temperature and acidification. The enhanced bottom‐up forcing boosted nematode densities but impoverished the functional and trophic diversity of nematode metacommunities. The combined climate stressors further homogenized meiofauna communities across habitats. Under present‐day conditions metacommunities were structured by habitat type, but under future conditions they showed an unstructured random pattern with fast‐growing generalist species dominating the communities of all habitats. Homogenization was likely driven by local species extinctions, reducing interspecific competition that otherwise could have prevented single species from dominating multiple niches. Our findings reveal that climate change may simplify metacommunity structure and prompt biodiversity loss, which may affect the biological organization and resilience of marine communities.

Continue reading ‘Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species’

A future 1.2 °C increase in ocean temperature alters the quality of mangrove habitats for marine plants and animals

Highlights
• Mangrove habitats are more resilient to climate change than other habitats.

• Climate change might have positive effects on mangrove-root species communities.

• Using mesocosms we show that an increase of 1.2 °C leads to community homogenisation.

• Warming also led to diversity loss and flattening of mangrove root epibiont communities.

• Juvenile fish altered their use of mangrove habitats under warming and acidification.

Abstract
Global climate stressors, like ocean warming and acidification, contribute to the erosion of structural complexity in marine foundation habitats by promoting the growth of low-relief turf, increasing grazing pressure on structurally complex marine vegetation, and by directly affecting the growth and survival of foundation species. Because mangrove roots are woody and their epibionts are used to ever-changing conditions in highly variable environments, mangrove habitats may be more resilient to global change stressors than other marine foundation species. Using a large-scale mesocosm experiment, we examined how ocean warming and acidification, under a reduced carbon emission scenario, affect the composition and structural complexity of mangrove epibiont communities and the use of mangrove habitat by juvenile fishes. We demonstrate that even a modest increase in seawater temperature of 1.2 °C leads to the homogenisation and flattening of mangrove root epibiont communities. Warming led to a 24% increase in the overall cover of algal epibionts on roots but the diversity of the epibiont species decreased by 33%. Epibiont structural complexity decreased owing to the shorter stature of weedy algal turfs which prospered under elevated temperature. Juvenile fishes showed alterations in mangrove habitat use with ocean warming and acidification, but these were independent of changes to the root epibiont community. We reveal that the quality of apparently resilient mangrove habitats and their perceived value as habitat for associated fauna are still vulnerable under a globally reduced carbon emission scenario.

Continue reading ‘A future 1.2 °C increase in ocean temperature alters the quality of mangrove habitats for marine plants and animals’

How calorie-rich food could help marine calcifiers in a CO2-rich future

Increasing carbon emissions not only enrich oceans with CO2 but also make them more acidic. This acidifying process has caused considerable concern because laboratory studies show that ocean acidification impairs calcification (or shell building) and survival of calcifiers by the end of this century. Whether this impairment in shell building also occurs in natural communities remains largely unexplored, but requires re-examination because of the recent counterintuitive finding that populations of calcifiers can be boosted by CO2 enrichment. Using natural CO2 vents, we found that ocean acidification resulted in the production of thicker, more crystalline and more mechanically resilient shells of a herbivorous gastropod, which was associated with the consumption of energy-enriched food (i.e. algae). This discovery suggests that boosted energy transfer may not only compensate for the energetic burden of ocean acidification but also enable calcifiers to build energetically costly shells that are robust to acidified conditions. We unlock a possible mechanism underlying the persistence of calcifiers in acidifying oceans.

Continue reading ‘How calorie-rich food could help marine calcifiers in a CO2-rich future’

Sensitivity of planktic foraminiferal test bulk density to ocean acidification

The anthropogenic CO2 accumulating in the ocean is lowering seawater carbonate ion concentration and may reduce calcification rates of marine calcareous organisms. Several proxies based on test weights of planktic foraminifera have been used to evaluate the impact of ocean acidification on these organisms. Unfortunately, because of the absence of a method to evaluate the bulk density of a test, the impact of seawater carbonate chemistry on test calcification is still not fully understood. In this study, we measured bulk densities of living Globigerina bulloides (planktic foraminifera) tests with an X-ray micro-computed tomography (XMCT) scanner and compared them with ambient seawater characteristics. Results demonstrated that test bulk densities were controlled by ambient seawater carbonate ion concentrations and that changes of test bulk densities were accompanied by changes in micron to submicron scale porosity of internal ultrastructure. These results suggest that alteration of the bulk density of foraminiferal tests due to acidification of ambient seawater can be directly observed by XMCT scanning. A useful metric of calcification intensity would therefore be physical measurements of test densities with XMCT.

Continue reading ‘Sensitivity of planktic foraminiferal test bulk density to ocean acidification’

Calcite dissolution rates in seawater: lab vs. in-situ measurements and inhibition by organic matter

Highlights

• Calcite dissolution in lab and in-situ exhibits the same dissolution mechanisms.

• In-situ dissolution rates are likely inhibited by dissolved organic carbon.

• Orthophosphate has no effect on seawater calcite dissolution rates from pH 5.5 to 7.5.

• Previous in-situ dissolution rates fall between bounds established by our measurements.

• Rate measurements suggest need to reevaluate marine carbonate system equilibria.

Abstract

Ocean acidification from fossil fuel burning is lowering the mean global ocean saturation state (Ω = ), thus increasing the thermodynamic driving force for calcium carbonate minerals to dissolve. This dissolution process will eventually neutralize the input of anthropogenic CO2, but the relationship between Ω and calcite dissolution rates in seawater is still debated. Recent advances have also revealed that spectrophotometric measurements of seawater pHs, and therefore in-situ Ωs, are systematically lower than pHs/Ωs calculated from measurements of alkalinity (Alk) and total dissolved inorganic carbon (DIC). The calcite saturation horizon, defined as the depth in the water column where Ω = 1, therefore shifts by ~5–10% depending on the parameters used to calculate Ω. The “true” saturation horizon remains unknown. To resolve these issues, we developed a new in-situ reactor and measured dissolution rates of 13C-labeled inorganic calcite at four stations across a transect of the North Pacific Ocean. In-situ saturation was calculated using both Alk-DIC (Ω(Alk, DIC)) and Alk-pH (Ω(Alk, pH)) pairs. We compare in-situ dissolution rates with rates measured in filtered, poisoned, UV-treated seawater at 5 and 21 °C under laboratory conditions. We observe in-situ dissolution above Ω(Alk, DIC) = 1, but not above Ω(Alk, pH) = 1. We emphasize that marine carbonate system equilibria should be reevaluated and that care should be taken when using proxies calibrated to historical Ω(Alk, DIC). Our results further demonstrate that calcite dissolution rates are slower in-situ than in the lab by a factor of ~4, but that they each possess similar reaction orders (n) when fit to the empirical Rate = k(1-Ω)n equation. The reaction orders are n < 1 for 0.8 < Ω < 1 and n = 4.7 for 0 < Ω < 0.8, with the kink in rates at Ωcrit = 0.8 being consistent with a mechanistic transition from step edge retreat to homogenous etch pit formation. We reconcile the offset between lab and in-situ rates by dissolving calcite in the presence of elevated orthophosphate (20 μm) and dissolved organic carbon (DOC) concentrations, where DOC is in the form of oxalic acid (20 μm), gallic acid (20 μm), and d-glucose (100 μm). We find that soluble reactive phosphate has no effect on calcite dissolution rates from pH 5.5–7.5, but the addition of DOC in the form of d-glucose and oxalic acid slows laboratory dissolution rates to match in-situ observations, potentially by inhibiting the retreat rate of steps on the calcite surface. Our lab and in-situ rate data form an envelope around previous in-situ dissolution measurements and may be considered outer bounds for dissolution rates in low/high DOC waters. The lower bound (high DOC) is most realistic for particles formed in, and sinking out of, surface waters, and is described by R(mol cm-2 s-1) = 10–14.3±0.2(1-Ω)0.11±0.1 for 0.8 < Ω < 1, and R(mol cm-2 s-1) = 10–10.8±0.4(1-Ω)4.7±0.7 for 0 < Ω < 0.8. These rate equations are derived from in-situ measurements and may be readily implemented into marine geochemical models to describe water column calcite dissolution.

Continue reading ‘Calcite dissolution rates in seawater: lab vs. in-situ measurements and inhibition by organic matter’

Dynamics of benthic metabolism, O2, and pCO2 in a temperate seagrass meadow

Seagrass meadows play an important role in “blue carbon” sequestration and storage, but their dynamic metabolism is not fully understood. In a dense Zostera marina meadow, we measured benthic O2 fluxes by aquatic eddy covariance, water column concentrations of O2, and partial pressures of CO2 (pCO2) over 21 full days during peak growing season in April and June. Seagrass metabolism, derived from the O2 flux, varied markedly between the 2 months as biomass accumulated and water temperature increased from 16°C to 28°C, triggering a twofold increase in respiration and a trophic shift of the seagrass meadow from being a carbon sink to a carbon source. Seagrass metabolism was the major driver of diurnal fluctuations in water column O2 concentration and pCO2, ranging from 173 to 377 μmol L−1 and 193 to 859 ppmv, respectively. This 4.5‐fold variation in pCO2 was observed despite buffering by the carbonate system. Hysteresis in diurnal water column pCO2 vs. O2 concentration was attributed to storage of O2 and CO2 in seagrass tissue, air–water exchange of O2 and CO2, and CO2 storage in surface sediment. There was a ~ 1:1 mol‐to‐mol stoichiometric relationship between diurnal fluctuations in concentrations of O2 and dissolved inorganic carbon. Our measurements showed no stimulation of photosynthesis at high CO2 and low O2 concentrations, even though CO2 reached levels used in IPCC ocean acidification scenarios. This field study does not support the notion that seagrass meadows may be “winners” in future oceans with elevated CO2 concentrations and more frequent temperature extremes.

Continue reading ‘Dynamics of benthic metabolism, O2, and pCO2 in a temperate seagrass meadow’


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Ocean acidification in the IPCC AR5 WG II

OUP book