Activity and ventilation-induced variations of postbranchial oxygen tensions in the isopod Saduria entomon

Variations in postbranchial oxygen tensions were studied in vivo in the brackish water isopod Saduria entomon collected from the Baltic Sea in 1992. Haemolymph oxygen tensions were highly influenced by activity. Resting isopods showed small and regular variations in haemolymph oxygen tensions, while a sudden burst of activity caused an immediate reduction in oxygen tension. Periods of no ventilation caused anoxic haemolymph in less than 3 to 4 min. Haemolymph oxygen tension responds rapidly, within seconds to minutes, to changes in isopod activity. Oxygen uptake rates calculated from oxygen tension difference, gill area and membrane thickness were compared with measured values. Permeability studies showed that only 30% of the gill area was effective in oxygen transfer. The present study has confirmed earlier measured oxygen uptake rates and reevaluated the role of the gills as respiratory organs. Postbranchial oxygen tension was established as a function of external steady state oxygen tensions and the intrinsic diffusive conductance was estimated.     

Ventilatory responses of the shrimp Palaemon adspersus to sublethal concentrations of crude oil extract

The shrimp Palaemon adspersus Rathke was exposed to the water soluble fraction (WSF: 50; 100; 200 ppb) of North Sea crude oil. The ventilatory behaviour, measured with impedance techniques, was followed for 2 wk and in a subsequent recovery period for 5 wk. Exposure to WSF caused a gradual increase in arrhythmic scaphognathite activity. After 6 d of exposure to 200 ppb shrimps spent more than 50% of the time beating arrhythmically, persisting and sometimes increasing to 100% during the remainder of the exposure period. In the 100 and 50 ppb groups, the proportion of time spent beating arrhythmically increased gradually with exposure time reaching 30 and 20% respectively. After 4 wk in clean seawater no signs of recovery were evident for individuals previously exposed to 200 ppb while those previously in 50 ppb had all recovered. After 5 wk those previously in 100 ppb had recovered and the 200 ppb group showed signs of recovery. The disturbances in ventilatory behaviour when exposed to WSF is considered to be due to damage to gill membranes or to nerve tissue, especially to the neurons in the suboesophageal ganglion controlling scaphognathite activity.Supported by the Environmental Research Programme under the Commission of European Communities (Contribution No. ENV/350/DK (G))     

A cognitive approach to the post-Soviet Central Asian pasture puzzle: new data from Kyrgyzstan

Regional Environmental Change - Despite internationally recognized definitions, there remains debate over what constitutes ‘actual’ degradation in various agro-pastoral contexts. This...     

Effects of emersion and elevated haemolymph ammonia on haemocyanin–oxygen affinity of Cancer pagurus

The subtidal crab Cancer pagurus (L.) experiences involuntary periods of emersion associated with practices used in their marketing and distribution. During 24 h emersion, impaired gill function caused an increase of circulating total ammonia (TA=NH₃+NH₄⁺) of 0.35 mmol TA l^-1 (167%). The oxygen-binding characteristics of the haemocyanin of C. pagurus were examined at 10°C in the presence of total ammonia (0.2-1.0 mmol TA l^-1). The haemocyanin-oxygen affinity was decreased in the presence of TA ((logP₅₀/(log[TA]=0.16). Emersion induced significant acidosis and elevated circulating levels of haemolymph TA, lactate and urate, but all had returned to normal levels within 24 h of re-immersion. The accumulation of haemocyanin-modulating substances during 24 h emersion compensated partially (40%) for the effect of the acidosis, but the net effect of the emersion period was a significant decrease in oxygen affinity, corresponding to an increase of P₅₀ (10°C ) from 1.24 kPa (immersed) to 1.96 kPa (24 h emersion). The implications of the findings are considered in terms of the effects and adaptations to emersion.     

Metal mobilization in soil by two structurally defined polyphenols

Polyphenols including tannins comprise a large percentage of plant detritus such as leaf litter, and affect soil processes including metal dynamics. We tested the effects of tannins on soil metal mobilization by determining the binding stoichiometries of two model polyphenols to Al(III) and Fe(III) using micelle-mediated separation and inductively coupled plasma optical emission spectroscopy (ICP-OES). By fitting the data to the Langmuir model we found the higher molecular weight polyphenol (oenothein B) was able to bind more metal than the smaller polyphenol (epigallocatechin gallate, EGCg). For example, oenothein B bound 9.43 mol Fe mol^?1, while EGCg bound 4.41 mol of Fe mol^?1. Using the parameters from the binding model, we applied the Langmuir model for competitive binding to predict binding for mixtures of Al(III) and Fe(III). Using the parameters from the single metal experiments and information about polyphenol sorption to soils we built a model to predict metal mobilization from soils amended with polyphenols. We tested the model with three natural soils and found that it predicted mobilization of Fe and Al with r² = 0.92 and r² = 0.88, respectively. The amount of metal that was mobilized was directly proportional to the maximum amount of metal bound to the polyphenol. The secondary parameter in each model was the amount of weak organically chelated Fe or Al that was in the soil. This study provides the first compound-specific information about how natural polyphenols interact with metals in the environment. We propose a model that is applicable to developing phytochelation agents for metal detoxification, and we discuss how tannins may play a role in metal mobilization from soils.     

Exploring the emergence of a tipping point for conservation with increased recognition of social considerations

Despite a common understanding of the harmful impacts of Western conservation models that separate people from nature, widespread progress toward incorporating socioeconomic, political, cultural, and spiritual considerations in conservation practice is lacking. For some, the concept of nature-based solutions (NbS) is seen as an interdisciplinary and holistic pathway to better integrate human well-being in conservation. We examined how conservation practitioners in the United States view NbS and how social considerations are or are not incorporated in conservation adaptation projects. We interviewed 28 individuals working on 15 different such projects associated with the Wildlife Conservation Society's Climate Adaptation Fund. We completed 2 rounds of iterative coding in NVivo 12.6.1 to identify in the full text of all interview responses an a priori set of themes related to our research questions and emergent themes. Many respondents saw this moment as a tipping point for the field (one in which the perceived values of social considerations are increasing in conservation practice) (76%) and that social justice concerns and the need to overcome racist and colonial roots of Western conservation have risen to the forefront. Respondents also tentatively agreed that NbS in conservation could support social and ecological outcomes for conservation, but that it was far from guaranteed. Despite individual intention and awareness among practitioners to incorporate social considerations in conservation practice, structural barriers, including limited funding and inflexible grant structures, continue to constrain systemic change. Ultimately, systemic changes that address power and justice in policy and practice are required to leverage this moment to more fully address social considerations in conservation.     

Social comfort zones for transformative conservation decisions in a changing climate

Novel management interventions intended to mitigate the impacts of climate change on biodiversity are increasingly being considered by scientists and practitioners. However, resistance to more transformative interventions remains common across both specialist and lay communities and is generally assumed to be strongly entrenched. We used a decision-pathways survey of the public in Canada and the United States (n = 1490) to test two propositions relating to climate-motivated interventions for conservation: most public groups are uncomfortable with interventionist options for conserving biodiversity and given the strong values basis for preferences regarding biodiversity and natural systems more broadly, people are unlikely to change their minds. Our pathways design tested and retested levels of comfort with interventions for forest ecosystems at three different points in the survey. Comfort was reexamined given different nudges (including new information from trusted experts) and in reference to a particular species (bristlecone pine [Pinus longaeva]). In contrast with expectations of public unease, baseline levels of public comfort with climate interventions in forests was moderately high (46% comfortable) and increased further when respondents were given new information and the opportunity to change their choice after consideration of a particular species. People who were initially comfortable with interventions tended to remain so (79%), whereas 42% of those who were initially uncomfortable and 40% of those who were uncertain shifted to comfortable by the end of the survey. In short and across questions, comfort levels with interventions were high, and where discomfort or uncertainty existed, such positions did not appear to be strongly held. We argue that a new decision logic, one based on anthropogenic responsibility, is beginning to replace a default reluctance to intervene with nature.     

Some effects of hypoxia and medium ammonia enrichment on efflux rates and circulating levels of ammonia inNephrops norvegicus

Eutrophication has been reported for autumn months in regions of the Kattegat/Skagerrak, causing stress to bottom-living organisms. The present studies, undertaken in April (1989), investigated the effects of hypoxia and high ammonia levels in the burrowing decapodNephrops norvegicus (L.). The net ammonia efflux rates and circulating ammonia levels at 6 and 12°C, at normoxia [partial pressure of O₂ in the water (torr),P _wO₂ = 155 torr)] and hypoxiaP _wO₂ = 24 torr) in normal seawater and ammonia-enriched (300µmol ammonia l^–1) seawater were examined. The hourly weight-specific efflux rates were very variable and in all groups included some individuals which showed periods of no net efflux, or even a net uptake of ammonia. At each temperature, net efflux-rate differences due to treatments were not significant (P>0.05; ANOVA, in all cases) and only the differences between the net efflux rates of the normoxic groups were significantly affected by temperature (P<0.05; ANOVA). Circulating ammonia levels were also variable, and at 6°C the ammonia-enriched groups had significantly higher weight-specific blood ammonia content values than the normoxic group (P<0.05 in both cases). A net uptake of ammonia occurred in ammoniaenriched conditions — probably along a reversed NH ₄ ⁺ gradient, as downhill pNH₃ gradients were maintained in all groups — and may represent the only means by which some branchial efflux of ammonia could proceed.     

Effects of hypoxia on the respiratory and circulatory regulation of Nephrops norvegicus

The burrowing decapod Nephrops norvegicus (L.) was kept under various degrees of hypoxia in order to measure respiration, heart rate, scaphognathite rate, haemolymph oxygen content and pH. An emergence reaction to hypoxia occurred only in dim light (<10^-2 m-c) or darkness, but after 10 d of moderate hypoxia the decapods showed no emergence response at all. The weight specific respiration of quiescent individuals was relatively low and increased only slightly in hypoxia (P_wO₂=40 torr). Heart rate, about 50 beats min^-1, changed little during hypoxia, down to P_wO₂=40 torr, whereas scaphognathite rates rose from about 60 beats min^-1 at normoxia to peak at 120 beats min^-1 at P_wO₂=40 torr. The oxygen extraction efficiency (E) remained at 20 to 30% during the first hour of hypoxia then rose gradually to maximum values of 30 to 40%. A small respiratory alkalosis of the blood became evident only after 4h of hypoxia (P_wO₂=50 torr). Normoxic postbranchial O₂ tensions (P_aO₂) were low (25–30 torr) and showed only a small decline during hypoxia. Over 10 to 13 d in moderate hypoxia an effective biosynthesis of 0.024 mM haemocyanin individual^-1 d^-1 occurred in fed decapods, whereas controls (normoxic) showed no significant change in pigment levels. A linear relationship between oxygen carrying capacity and haemocyanin concentration was found. It is contended that N. norvegicus is better able to cope with periodic exposure to hypoxia when food of sufficient quantity and quality is available.     

Haemocyanin concentration of juvenile lobsters (Homarus gammarus) in relation to moulting cycle and feeding conditions

Groups of laboratory-reared, juvenile lobsters (Homarus gammarus, 40–50 g wet weight) were given different types of food (shrimp, mixed invertebrates and pellets, bivalves, starved) for a period of 22 wk. Haemocyanin concentration was measured weekly, moult stage and moultings noted. Haemocyanin concentration decreased rapidly in the starved group (from 0.8–0.6 to 0.2 mM). The group fed with bivalves showed a small decline with time, to 0.5–0.3 mM at the end of the period, indicating a deficient diet. The haemocyanin in the other groups did not change significantly during the experiment. Moultings decreased in frequency and the intermoult period was prolonged when the quality of food was decreased, and in the starved group moulting ceased completely after 1.5 months. Haemocyanin concentration was lowest immediately after moult and increased gradually through stages C and D. Lobsters that were starved or maintained on the bivalve diet did not reach the same premoult haemocyanin levels as those fed with shrimps and mixed food.