Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ...ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 'ambient' and 7.65 a worst case 'ocean acidification' scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO3) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification.
Under globally accelerating rates of ecosystem degradation, maintaining ecosystem function is a priority to avoid loss of valuable ecosystem services. Two factors are important: changes to the ...disturbance regime (stresses imposed) and resilience of biodiversity and ecosystem functions (the ecosystem’s capacity to respond to change). Various attributes at different scales of ecological organisation confer resilience (from individual species to communities at landscape scales), but it is critical to understand how these attributes interact to inform how ecosystem function changes with disturbances that vary in intensity, spatial extent, and frequency. Individual species attributes influence their resistance, while attributes at the landscape-scale influence recovery of communities and function. Understanding resilience to disturbances requires defining the characteristics of a resilient community at multiple scales.
With globally accelerating extinction rates, ecologists and society are focussed on protecting ecosystem function.Resilience of ecosystem function occurs at multiple scales of ecological organisation: individual, population, and community.Attributes at the individual species scale increase resistance, while attributes at the landscape scale (population and community) influence recovery.We explore how different combinations of scale-dependent resilience attributes are linked to resilience as disturbance regimes vary in their intensity, spatial extent, and frequency.Considering multiple scales of resilience attributes allows exploration of how, when, and why different aspects of biodiversity enable the persistence of function under future scenarios of multiple, cumulative, and intensified disturbance regimes.
Coastal ecosystems that are characterized by kelp forests encounter daily pH fluctuations, driven by photosynthesis and respiration, which are larger than pH changes owing to ocean acidification (OA) ...projected for surface ocean waters by 2100. We investigated whether mimicry of biologically mediated diurnal shifts in pH—based for the first time on pH time-series measurements within a kelp forest—would offset or amplify the negative effects of OA on calcifiers. In a 40-day laboratory experiment, the calcifying coralline macroalga, Arthrocardia corymbosa, was exposed to two mean pH treatments (8.05 or 7.65). For each mean, two experimental pH manipulations were applied. In one treatment, pH was held constant. In the second treatment, pH was manipulated around the mean (as a step-function), 0.4 pH units higher during daylight and 0.4 units lower during darkness to approximate diurnal fluctuations in a kelp forest. In all cases, growth rates were lower at a reduced mean pH, and fluctuations in pH acted additively to further reduce growth. Photosynthesis, recruitment and elemental composition did not change with pH, but δ13C increased at lower mean pH. Including environmental heterogeneity in experimental design will assist with a more accurate assessment of the responses of calcifiers to OA.
The suspension feeding bivalve Austrovenus stutchburyi is a key species on intertidal sandflats in New Zealand, affecting the appearance and functioning of these systems, but is susceptible to ...several environmental stressors including sedimentation. Previous studies into the effect of this species on ecosystem function have been restricted in space and time, limiting our ability to infer the effect of habitat change on functioning. We examined the effect of Austrovenus on benthic primary production and nutrient dynamics at two sites, one sandy, the other composed of muddy-sand to determine whether sedimentary environment alters this key species' role. At each site we established large (16 m(2)) plots of two types, Austrovenus addition and removal. In winter and summer we deployed light and dark benthic chambers to quantify oxygen and nutrient fluxes and measured sediment denitrification enzyme activity to assess denitrification potential. Rates of gross primary production (GPP) and ammonium uptake were significantly increased when Austrovenus was added, relative to removed, at the sandy site (GPP, 1.5 times greater in winter and summer; ammonium uptake, 8 times greater in summer; 3-factor analysis of variance (ANOVA), p<0.05). Denitrification potential was also elevated in Austrovenus addition plots at the sandy site in summer (by 1.6 times, p<0.1). In contrast, there was no effect of Austrovenus treatment on any of these variables at the muddy-sand site, and overall rates tended to be lower at the muddy-sand site, relative to the sandy site (e.g. GPP was 2.1 to 3.4 times lower in winter and summer, respectively, p<0.001). Our results suggest that the positive effects of Austrovenus on system productivity and denitrification potential is limited at a muddy-sand site compared to a sandy site, and reveal the importance of considering sedimentary environment when examining the effect of key species on ecosystem function.
Coastal ecosystems are important because of the vital ecosystem functions and services they provide, but many are threatened by eutrophication and hypoxia. This results in loss of biodiversity and ...subsequent changes in ecosystem functioning. Consequently, the need for empirical field studies regarding biodiversity-ecosystem functioning in coastal areas has been emphasized. The present field study quantified the links between benthic macrofaunal communities (abundance, biomass, and species richness), sediment oxygen consumption, and solute fluxes (NO₃⁻ + NO₂⁻, NH₄⁺, PO₄³⁻, SiO₄, Fe, Mn) along a 7.5-km natural gradient of seasonal hypoxia in the coastal northern Baltic Sea. Sampling was done in late August 2010 in the middle archipelago zone of the Hanko peninsula, Finland. As predicted, the macrofaunal communities were decimated with increasing hypoxia, and the nutrient transformation processes were changed at the sediment-water interface, with notably higher effluxes of phosphate and ammonium from the sediment. Solute fluxes varied even during normoxia, which implies a high context-dependency, and could be explained by even small variations in environmental variables such as organic matter and C/N ratios. Importantly, the low diversity benthic macrofaunal communities, which were dominated by Macoma balthica and the invasive Marenzelleria spp., had a large influence on the solute fluxes, especially under normoxia, but also under hypoxia.
We use concomitant radon (222Rn, a natural groundwater tracer) and nutrient time series observations upstream and downstream of two New Zealand estuarine intertidal flats to assess porewater exchange ...rates and/or submarine groundwater discharge (SGD) and their influence on surface water nutrient dynamics. A detailed radon mass balance model and an uncertainty analysis revealed porewater exchange rates of 27±7 and 14±6cmd−1 (or cm3cm−2d−1) in Waikareao and Te Puna, respectively. The upscaled porewater exchange rates were slightly higher than the creek input upstream of both intertidal flats. A water and salt balance compared to the radon balance indicated that about 16% (Waikareao) and 49% (Te Puna) of the total volume of porewater exchange consisted of fresh SGD and the remaining was related to seawater recirculation in intertidal sediments. Porewater exchange in Waikareao released about 1.9- and 1.6-fold more total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) than creek inputs at the upstream end of the intertidal flat even though observations followed a 140mm rain event. Dissolved organic nitrogen (DON) accounted for about 25% of TDN in shallow porewater. Nitrate dominated the nitrogen pool in Waikareao and ammonium was the main form of nitrogen in Te Puna porewaters. These dominant porewater N species were reflected in the surface waters that showed a relative enrichment of nitrate in Waikareao and ammonium in Te Puna as upstream waters travel to the downstream station and collect seeping porewater along the way. We suggest that porewater exchange may act as a buffered nutrient source to the estuary, continually releasing nutrients to surface waters and potentially sustaining primary production when other nutrient inputs cease. This study illustrates that combining bottom up (i.e., porewater exchange flux estimates) and top down (i.e., nutrient response and transformations in the water column) evidence may provide deeper insight when assessing the contribution of porewater to nutrient dynamics in estuaries.
•We use two concomitant time series stations to resolve a radon mass balance.•Propagated uncertainties were 26–43% of the estimated porewater exchange rate.•Porewater-derived nitrogen inputs were usually greater than upstream river inputs.•Porewater exchange changed nutrient speciation as estuarine waters collected seeping porewater.
A key challenge in environmental management is determining how to manage multiple ecosystem services (ES) simultaneously, to ensure efficient and sustainable use of the environment and its resources. ...In marine environments, the spatial assessment of ES is lagging as a result of data-scarcity and modelling complexity. Applying mechanistic models to link ecological processes with ecosystem functions and services to assess areas of high ES potential can bridge this gap and accommodate assessments of functional differences between service providers. Here, we applied an ecosystem principles approach to assess ES potential for food provision, water quality regulation, nitrogen removal, and sediment stabilisation, provided by two estuarine bivalves (Austrovenus stutchburyi and Paphies australis) that differ in habitat association (broad and narrow distributions), to gain insight into the utility of these models for local-scale management. Maps of individual ES displayed differing patterns related to habitat associations of the species providing them, with variation in the quantities of services being delivered and locations of importance. Areas of importance for the provision of multiple services (number of services provided and their combined intensity per species) were assessed using hotspot analyses, which suggested that areas of high shellfish density at the harbour entrances were important for ES multifunctionality. A targeted management approach that includes environmental context, rather than a focus solely on the protection of high-density shellfish areas, is required to sustain the provision of individual ES.
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•Ecosystem services (ES) can be predicted from underlying ecological principles•Principles were formulated to link shellfish-mediated processes to human benefits•Spatial patterns of single and combined ES were compared for two shellfish species•Variation in ES provision were driven by species' habitat associations and density•ES models can inform environmental management, scenario testing, and restoration
Metabolic processes have the potential to modulate the effects of ocean acidification (OA) in nearshore macroalgal beds. We investigated whether natural mixed assemblages of the articulate coralline ...macroalga Arthrocardia corymbosa and understory crustose coralline algae (CCA) altered pH and O₂ concentrations within and immediately above their canopies. In a unidirectional flume, we tested the effect of water velocity (0–0.1 m s−1), bulk seawater pH (ambient pH 8.05, and pH 7.65), and irradiance (photosynthetically saturating light and darkness) on pH and O₂ concentration gradients, and the derived concentration boundary layer (CBL) thickness. At bulk seawater pH 7.65 and slow velocities (0 and 0.015 m s−1), pH at the CCA surface increased to 7.90–8.00 in the light. Although these manipulations were short term, this indicates a potential daytime buffering capacity that could alleviate the effects of OA. Photosynthetic activity also increased O₂ concentrations at the surface of the CCA. However, this moderating capacity was flow dependent; the CBL thickness decreased from an average of 26.8 mm from the CCA surface at 0.015 m s−1 to 4.1 mm at 0.04 m s−1. The reverse trends occurred in the dark, with respiration causing pH and O₂ concentrations to decrease at the CCA surface. At all flow velocities the CBL thicknesses (up to 68 mm) were much greater than those previously published, indicating that the presence of canopies can alter the CBL substantially. In situ, the height of macroalgal canopies can be an order of magnitude larger than those used here, indicating that the degree of buffering to OA will be context dependent.
To quantify the effects of a future climate on three morphologically different lakes that varied in trophic status from oligo-mesotrophic to highly eutrophic, we applied the one-dimensional lake ...ecosystem model DYRESM-CAEDYM to oligo-mesotrophic Lake Okareka, eutrophic Lake Rotoehu, both in the temperate Bay of Plenty region, and highly eutrophic Lake Ellesmere, in the temperate Canterbury region, New Zealand. All three models were calibrated for a three-year period and validated for a separate two-year period. The model simulations generally showed good agreement with observed data for water column temperature, dissolved oxygen (DO), total phosphorus (TP), total nitrogen (TN) and chlorophyll a (Chl a) concentrations. To represent a possible future climate at the end of this century, mean annual changes in air temperature by 2100, derived from the IPCC A2 scenario downscaled for these lake regions, were added to the daily baseline temperatures for years 2002–2007. Lake model simulations using this future climate scenario indicate differential increases in eutrophication in all three lakes, especially during summer months. The predicted effects on annual mean surface water concentrations of TP, TN and Chl a will be equivalent to the effects of increasing external TN and TP loading by 25–50%. Simulations for the polymictic, eutrophic Lake Rotoehu further indicate that cyanophytes will be more abundant in the future climate, increasing by >15% in their contribution to annual mean Chl a. Therefore, future climate effects should be taken into account in the long-term planning and implementation of lake management as strategies may need to be refined and adapted to preserve or improve the present-day lake water quality.
The quantification of ecosystem services (ES) remains challenging and can result in biases towards data-rich ES in management. For infaunal bivalves, little quantitative in situ data are available on ...the ES they provide, and differences between functionally similar species in different habitats are rarely considered. Here, we aimed to measure and compare the ecosystem functions (primary production, nutrient processing, water clearance rates) underpinning water quality regulation in an estuarine intertidal and subtidal bivalve habitat (dominated by Austrovenus stutchburyi and Paphies australis respectively). In situ benthic chambers were used to measure sediment-water column solute fluxes (NH
4
+
, N
2
, O
2
) and clearance rates which were scaled up (accounting for habitat differences; e.g. inundation period) to daily estimates of ES potential. Higher hourly microphytobenthic productivity, nitrogen recycling and water filtration were observed for the intertidal bivalve habitat. These differences were attributed to environmental differences rather than differences in bivalve biomass. However, scaling these rates to daily ES estimates showed that inundation period will restrict water quality regulating services in the intertidal. Measuring multiple ecosystem functions in situ provides an important step forward in ES quantification and accounts for ecological complexity, feedbacks and highlights habitat-specific differences in how functionally similar species contribute to ES.
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