Search

The immune precipitates of high-density lipoprotein of duck serum with rabbit antisera are active on an esterase substrate, while the high-density lipoprotein itself is not active. The immune precipitates formed by high-density lipoprotein with isolated immunoglobulins, either in agar gel or in liquid medium, were also shown to be inactive, Such inactive immune precipitates can become active through interaction with a component of rabbit serum. Investigations on the conditions of the reaction and first observations concerning the nature of the activating component are reported. [ABSTRACT FROM AUTHOR]

Solute exchange between the sediment and the water column strongly influences water quality in aquatic ecosystems. Among the techniques available for in situ observation, only aquatic eddy covariance (AEC) can resolve the hourly dynamics of benthic fluxes, but only for few substances like oxygen. In micrometeorology, relaxed eddy accumulation (REA), a technique based on high‐frequency sampling conditioned by current direction, overcomes this limitation. We developed a portable prototype instrumentation platform to transfer REA to the sediment‐water interface of shallow aquatic ecosystems. In order to evaluate the sampling system, we configured the prototype for measuring oxygen fluxes and comparing them to simultaneous AEC measurements. In a river and two artificial lakes, at depths 1–3 m and 0.2 m above the sediment, we measured 15 oxygen flux pairs in fully developed turbulence during 8–15 min periods, ranging from −150 to 50 mmol m−2 day−1. The good agreement between REA and AEC fluxes (R2 = 0.94) shows the reliability of the conditional sampling system. REA represents a promising technique for exploring the sediment contribution to biogeochemical cycles in aquatic ecosystems. Plain Language Summary: Microbial activity at the bottom boundary of aquatic ecosystems, such as lakes, rivers and coastal areas, influences their water quality. Microorganisms decompose organic matter and release nutrients and greenhouse gases to the overlying open water. In shallow aquatic ecosystems, the release from the sediment surface can vary rapidly, especially with currents, but so far, no technique succeeds in monitoring dynamic fluxes at hourly timescales for a broad range of substances. In micrometeorology, relaxed eddy accumulation is a well‐established technique for monitoring the turbulent exchange of all kinds of compounds between land and atmosphere (including gas, aerosols and particles). Air is sampled conditionally for downward or upward motions and accumulated in separate containers. Concentration differences between sample pairs provide information on the fluxes. We developed a portable prototype, transferring this technique to quantify the exchange of nutrients and other compounds at the bottom boundary of shallow aquatic ecosystems. For its evaluation, we adapted the prototype to measure dissolved oxygen fluxes. The agreement of its measurements with fluxes measured by aquatic eddy covariance, our reference, shows the potential of this technique. It can now be used to quantify the exchange of major ions and of other substances including dissolved gases. Key Points: We developed a portable instrumentation platform for measuring benthic fluxes in shallow aquatic environments by relaxed eddy accumulationSimultaneous measurements of dissolved oxygen fluxes by aquatic eddy covariance showed the reliability of the conditional sampling techniqueThis work paves the way for exploring the dynamics of biogeochemical cycles in aquatic ecosystems at hourly time scales [ABSTRACT FROM AUTHOR]

Aim: In the context of intensifying threats of climate change on marine communities, ecological models are widely applied for conservation strategies, though polar studies remain scarce given the limited number of datasets available. Correlative (e.g. species distribution models, SDM) and mechanistic (e.g. dynamic energy budget models, DEB) modelling approaches are usually used independently in studies. Using both approaches in integrative, hybrid models could help to better estimate the species potential ecological niche, as mechanistic and correlative models complement each other very well, giving more insights into species potential response to fast‐changing environmental conditions. Location: The study focusses on the Baie du Morbihan, a silled basin located in the east of the Kerguelen Islands (sub‐Antarctic). Methods: A hybrid, correlative‐mechanistic model was implemented to predict the response of the endemic sea urchin Abatus cordatus (Verrill, 1876). We compared the performances of classic and integrated approaches to predict A. cordatus distribution according to two dates representing seasonal contrasts. Two integrated approaches were studied and performed by either (1) including the spatial projection of the DEB model as an input layer inside the SDM ('integrated SDM‐DEB') or (2) using a Bayesian procedure to use DEB model outputs as priors of the SDM ('integrated Bayesian' approach). Results: Results show higher performances of 'integrated Bayesian' approaches to evaluate A. cordatus potential ecological niche compared with 'classic' and 'integrated SDM‐DEB' methods. The influence of environmental conditions on model predictions is further captured with these Bayesian procedures and better highlights the environmental influence on the species‐predicted distribution. Model performance is good for the different simulations, and uncertainty in predictions is well‐highlighted. Main conclusions: The good performances of 'integrated Bayesian' approaches to estimate species potential ecological niche opens perspectives for future applications to a broad panel of natural examples, noteworthy for decision‐making and conservation management purposes. [ABSTRACT FROM AUTHOR]

Ocean warming (OW) and acidification (OA) are intensively investigated as they pose major threats to marine organism. However, little effort is dedicated to another collateral climate change stressor, the increased frequency, and intensity of storm events, here referred to as intensified hydrodynamics. A 2‐month experiment was performed to identify how OW and OA (temperature: 21°C; pHT: 7.7, 7.4; control: 17°C‐pHT7.9) affect the resistance to hydrodynamics in the sea urchin Paracentrotus lividus using an integrative approach that includes physiology, biomechanics, and behavior. Biomechanics was studied under both no‐flow condition at the tube foot (TF) scale and flow condition at the individual scale. For the former, TF disk adhesive properties (attachment strength, tenacity) and TF stem mechanical properties (breaking force, extensibility, tensile strength, stiffness, toughness) were evaluated. For the latter, resistance to flow was addressed as the flow velocity at which individuals detached. Under near‐ and far‐future OW and OA, individuals fully balanced their acid‐base status, but skeletal growth was halved. TF adhesive properties were not affected by treatments. Compared to the control, mechanical properties were in general improved under pHT7.7 while in the extreme treatment (21°C‐pHT7.4) breaking force was diminished. Three behavioral strategies were implemented by sea urchins and acted together to cope with flow: improving TF attachment, streamlining, and escaping. Behavioral responses varied according to treatment and flow velocity. For instance, individuals at 21°C‐pHT7.4 increased the density of attached TF at slow flows or controlled TF detachment at fast flows to compensate for weakened TF mechanical properties. They also showed an absence of streamlining favoring an escaping behavior as they ventured in a riskier faster movement at slow flows. At faster flows, the effects of OW and OA were detrimental causing earlier dislodgment. These plastic behaviors reflect a potential scope for acclimation in the field, where this species already experiences diel temperature and pH fluctuations. [ABSTRACT FROM AUTHOR]