Marsh macrophyte responses to inundation anticipate impacts of sea-level rise and indicate ongoing drowning of North Carolina marshes

In situ persistence of coastal marsh habitat as sea level rises depends on whether macrophytes induce compensatory accretion of the marsh surface. Experimental planters in two North Carolina marshes served to expose two dominant macrophyte species to six different elevations spanning 0.75 m (inundation durations 0.4–99 %). Spartina alterniflora and Juncus roemerianus exhibited similar responses—with production in planters suggesting initial increases and then demonstrating subsequent steep declines with increasing inundation, conforming to a segment of the ecophysiological parabola. Projecting inundation levels experienced by macrophytes in the planters onto adjacent marsh platforms revealed that neither species occupied elevations associated with increasing production. Declining macrophyte production with rising seas reduces both bioaccumulation of roots below-ground and baffle-induced sedimentation above-ground. By occupying only descending portions of the parabola, macrophytes in central North Carolina marshes are responding to rising water levels by progressive declines in production, ultimately leading to marsh drowning.     

Temperature and salinity interactively impact early juvenile development: a bottleneck in barnacle ontogeny

When juvenile mortality or juvenile growth is impacted by temperature and salinity, these factors have a substantial effect on recruitment success and population dynamics in benthic ecosystems. Using freshly settled cyprids of Amphibalanus improvisus, we investigated the combined effects of temperature (12, 20 and 28 °C) and salinity (5, 15 and 30 psu) on early juvenile stage performance. Mortality as well as size (basal diameter, dry weight, and ash-free dry weight) was monitored for a period of 40 days. Mortality was high (42–63 %) during the first week following attachment, regardless of the temperature and salinity treatments. Subsequently, mortality and size were interactively influenced by temperature and salinity. Highest mortality and lowest size of juveniles occurred at lowest temperature (12 °C) and salinity (5 psu). Apparently, low temperature (12 °C) narrowed the barnacles’ salinity tolerance. Juvenile barnacles constructed more shell material compared to body mass at high temperature and high salinity, while a reverse situation was observed at low temperature and low salinity. Our results demonstrate that environmental changes can directly and/or indirectly alter patterns of survivorship and size. Warming and desalination as predicted for the Baltic Sea in the course of climate change may, however, act antagonistically and compensate each other’s isolated effect on barnacles.     

Stable isotopes identify an ontogenetic niche expansion in Antarctic krill (Euphausia superba) from the South Shetland Islands, Antarctica

Antarctic krill (Euphausia superba) occupy a key position in the Southern Ocean linking primary production to secondary consumers. While krill is a dominant grazer of phytoplankton, it also consumes heterotrophic prey and the relative importance of these two resources may differ with ontogeny. We used stable isotope analyses to evaluate body size-dependent trophic and habitat shifts in krill during the austral summer around the South Shetland Islands, Antarctica. We found evidence for an asymmetric, ontogenetic niche expansion with adults of both sexes having higher and more variable δ¹⁵N values but consistent δ¹³C values in comparison with juveniles. This result suggests that while phytoplankton likely remains an important life-long resource, krill in our study area expand their dietary niche to include higher trophic food sources as body size increases. The broader dietary niches observed in adults may help buffer them from recent climate-driven shifts in phytoplankton communities that negatively affect larval or juvenile krill that rely predominately on autotrophic resources.     

Positive relationships between phenol oxidase activity and extractable phenolics in estuarine soils

Decomposition of recalcitrant materials such as phenolics is known to play a pivotal role in organic matter decomposition and nutrient cycling in estuaries. The specific goals of this study were to determine temporal and spatial variations of phenol oxidase and phenolics in estuarine soils, and to elucidate controlling factors for phenol oxidase activity. To achieve these goals, phenol oxidase activity and phenolic content were measured in soils developed along the side of an estuary in the Han River, Korea. Soil samples were collected in three locations with different vegetation: mud flats, Zizania-dominated soils, and Salix-dominated soils. Monthly measurements were also made in a Zizania-dominated site over a year period. Phenol oxidase activity varied between 0.00 and 0.28 diqc min^?1 g^?1, whilst phenolic content ranged from 0.0–10.5 μg g^?1. A correlation analysis revealed that phenol oxidase activity exhibited positive correlations with phenolic content in both seasonal and spatial data. The same relationship was found when the data were analysed separately for each site. Unlike peatlands or upland forest soils where negative correlations were often found between phenol oxidase activity and phenolics, substrate induction appears to account for the positive correlation in the present study.     

Unexpected control of soil carbon turnover by soil carbon concentration

Soils are a key component of the terrestrial carbon cycle as they contain the majority of terrestrial carbon. Soil microorganisms mainly control the accumulation and loss of this carbon. However, traditional concepts of soil carbon stabilisation failed so far to account for environmental and energetic constraints of microorganisms. Here, we demonstrate for the first time that these biological limitations might have the overall control on soil carbon stability. In a long-term experiment, we incubated ¹³C-labelled compost with natural soils at various soil carbon concentrations. Unexpectedly, we found that soil carbon turnover decreased with lower carbon concentration. We developed a conceptual model that explained these observations. In this model, two types of particles were submitted to random walk movement in the soil profile: soil organic matter substrate and microbial decomposers. Soil carbon turnover depended only on the likelihood of a decomposer particle to meet a substrate particle; in consequence, carbon turnover decreased with lower carbon concentration, like observed in the experiment. This conceptual model was able to simulate realistic depth profiles of soil carbon and soil carbon age. Our results, which are simply based on the application of a two-step kinetic, unmystify the stability of soil carbon and suggest that observations like high carbon ages in subsoil, stability of carbon in fallows and priming of soil carbon might be simply explained by the probability to be decomposed.     

The role of ecological context and predation risk-stimuli in revealing the true picture about the genetic basis of boldness evolution in fish

To showcase the importance of genotype × environment interactions and the presence of predation risk in the experimental assessment of boldness in fish, we investigated boldness in terms of feeding behavior and refuge use in two genetically different populations of juvenile carp (Cyprinus carpio) in two replicated experimental conditions in ponds and laboratory tanks. The populations were expected to exhibit genetic differences in boldness due to differential evolutionary adaptation to low-predation-risk pond aquaculture conditions. Boldness was measured in variants of open-field trials with and without implementation of additional predation risk-stimuli by angling on feeding spots. Without explicit implementation of risk, genotypes adapted to low-risk environments, i.e., domesticated mirror carp behaved consistently bolder than their less domesticated scaled conspecifics in the pond environment, but not in the laboratory environment. When we implemented artificial risk-stimuli by angling on previously safe feeding spots, boldness differences among genotypes also emerged in the laboratory environment, indicating strong genotype × environment effects on boldness behavior of carp. The expected genetic basis of boldness differences among genotypes was clearly supported in the pond environment, while the laboratory study revealed these patterns only under inclusion of explicit risk-stimuli. Our study thus underscores that boldness may involve both a basal component that is expressed independently of obvious predation risk (e.g., in open fields) and a component revealed in relation to explicit predation risk, and both dimensions may respond differently in behavioral tests.     

The onset of natural convection in lakes and reservoirs due to night time cooling

A theoretical model, based on linear stability analysis, is proposed to predict the onset of natural convection in lakes and reservoirs due to night time cooling. To such purpose, the system was modelled as a initially quiescent deep Boussinesq fluid reservoir, whose upper boundary temperature changes sinusoidally. From scaling analysis, it is found that critical onset times for convection are proportional to R ^−2/7, where R is a Rayleigh number including fluid properties and forcing frequency. The proportionality constant was found, from the solution of an eigenvalue problem, as a function of the Prandtl number. The onset time for convection was easily observed from experiments and quantitatively detected as a rapid increase of the RMS of the computed velocity field obtained using PIV. In this controlled conditions, differences close to 10% between predicted and observed times for the start of the convective flow was found. It is apparent from the present set of results that predictions are reasonable.     

Trend analyses of hierarchical pin-point cover data

The use of state-space models for analyzing longitudinal hierarchical pin-point plant cover data is demonstrated. The main advantages of using a state-space model are (1) that the observed variance is separated into sampling variance and the more interesting structural variance which are needed for quantifying prediction uncertainty, (2) that missing values or an unbalanced sampling design readily may be accounted for, and (3) that the structural equation easily may be expanded and made as complex as necessary for modeling longitudinal pin-point cover data, thus allowing the incorporation of the most important ecological processes in the state-space model without technical difficulties. Typically, there is considerable spatial variation in plant abundance, and this variation is modeled using the Pólya-Eggenberger distribution (a generalization of the beta-binomial distribution). To illustrate this method, longitudinal hierarchical pin-point data of Erica tetralix in wet Danish heathlands were analyzed, including and excluding autocorrelation and an environmental covariable in the state-space model. The pin-point plant cover data showed a significant decrease in the plant cover of E. tetralix in the period from 2004 to 2009, with an annual decrease of about 10% in the logit-transformed cover. The distribution of predicted plant cover at a given site the following year was calculated, including and excluding the information of an environmental covariable.     

Bridging the gap between the field and the lab: Environmental goods, policy maker input, and consequentiality

This paper explores the criterion validity of stated preference methods through experimental referenda that capture key characteristics of a stated preference survey for a proposed environmental program. In particular, we investigate whether advisory referenda, where participant votes have either known or unknown weight in the policy decision, can elicit values comparable to that of a standard, incentive-compatible referendum. When participants regard their votes as consequential, our results suggest there is no elicitation bias with advisory referenda. For advisory referenda where participants view their votes as inconsequential, and for purely hypothetical referenda, we observe elicitation bias.