Response of nitrogen dynamics in semi-natural and agricultural grassland soils to experimental variation in tide and salinity

In the framework of rehabilitation efforts to enhance the ecological value of closed-off estuaries, we studied the effects of restoring a tidal movement and seawater incursion on soil nitrogen conversion rates and vegetation response of semi-natural and agricultural grasslands in an outdoor mesocosm experiment. Intact soil monoliths including vegetation were collected in June 2004 on two locations on the shores of the Haringvliet lagoon in the south-western part of the Netherlands, which used to be a well-developed estuary before closure in 1970. For more than 1 year, soil monoliths were continuously subjected to a full-factorial combination of tidal treatment [stagnant/tidal (0.20 m amplitude)] and water type [(freshwater, oligohaline (salinity = 3)]. Soil, soil moisture and water nitrogen concentrations were monitored for a year, as well as vegetation response and nitrogen conversion rates in the soil. As expected, nitrogen mineralization rates were enhanced by the tidal treatment in comparison with the stagnant treatment. Denitrification rates however, were much less affected by tide and were even lower in the tidal treatments after 3 months in the agricultural grassland soils, implying that in general, soils were more oxic in the tidal treatments. Oligohaline treatments had virtually no effect on soil nitrogen conversion rates compared to freshwater treatments. Vegetation performance, however, was lower under saline conditions, especially in the semi-natural grassland. No further significant differences in response to the tidal and oligohaline treatments were found between the two soils although they differed strongly in soil characteristics. We conclude that if the rehabilitation measures in the former Haringvliet estuary are carried out as planned, drastic changes in soil nitrogen processes and vegetation composition will not occur.     

Relationships between benthic macrofauna and biogeochemical properties of sediments at different spatial scales and among different habitats in mangrove forests

In muddy intertidal sediments, there are reported complex interactions between the biological, physical and chemical properties of the sediment and the benthos that live in and on it. These are expected to be reflected in strong relationships between benthic animals and particular properties of the sediment, although some research has shown these relationships to be relatively weak. This study investigates the relationships between benthic macrofauna and biogeochemical properties of sediments within and among different habitats in multiple mangrove forests in a temperate estuary, in order to address the generality of any such relationships. Matched samples of benthos and sediment were collected from three habitats, which differed with respect to shading, the amounts of algae and leaf litter and the presence of pneumatophores. The sediment was sampled for water content, grain size, organic matter, chlorophylls a and b and colloidal and total carbohydrate.Spatial variation in sediment and benthos were significantly correlated across habitats in two of the three bays, but the sediment properties that contributed to differences between habitats and those that best correlated with the benthos varied among bays. In all bays, the single taxon that best correlated with the sediment was spionid polychaetes, but correlations were generally weak. There was no generality in the patterns of variation among the benthos or sedimentary properties among habitats. The benthos differed significantly among bays in all habitats, with large variation within and among sites. The sediment varied significantly at small scales in all habitats, but significant differences among bays were only found in two habitats. All spatial scales contributed to the total amount of variability in the sediment and there was little predictability from the patterns shown in one habitat to those in other habitats, or from one component of sediment to other components. Such variability suggests that there may be structural redundancy in this fauna, with different components of the benthos contributing to similar functions in different places. Such variability must be considered in experiments designed to understand relationships between ecological structure and function in these complex habitats and in any sampling studies to identify environmental impacts in these habitats.     

Natural selection on ecophysiological traits of a fern species in a temperate rainforest

Unlike other species of the genus Blechnum, the fern Blechnum chilense occurs in a wide range of habitats in Chilean temperate rainforest, from shaded forest understories to abandoned clearings and large gaps. We asked if contrasting light environments can exert differential selection on ecophysiological traits of B. chilense. We measured phenotypic selection on functional traits related to carbon gain: photosynthetic capacity (A _max), dark respiration rate (R _d), water use efficiency (WUE), leaf size and leaf thickness in populations growing in gaps and understorey environments. We assessed survival until reproductive stage and fecundity (sporangia production) as fitness components. In order to determine the potential evolutionary response of traits under selection, we estimated the genetic variation of these traits from clonally propagated individuals in common garden experiments. In gaps, survival of B. chilense was positively correlated with WUE and negatively correlated with leaf size. In contrast, survival in shaded understories was positively correlated with leaf size. We found positive directional fecundity selection on WUE in gaps population. In understories, ferns of lower R _d and greater leaf size showed greater fecundity. Thus, whereas control of water loss was optimized in gaps, light capture and net carbon balance were optimized in shaded understories. We found a significant genetic component of variation in WUE, R _d and leaf size. This study shows the potential for evolutionary responses to heterogeneous light environments in functional traits of B. chilense, a unique fern species able to occupy a broad successional niche in Chilean temperate rainforest.     

Innate versus adaptive immunity in sticklebacks: evidence for trade-offs from a selection experiment

In vertebrates, the immune system consists of two arms of different characteristics: the innate and the acquired immune response. Parasites that are only shortly exposed to the immune system are most efficiently attacked by fast, constitutive innate immune mechanisms. Here, we experimentally selected within four fish families for high innate resistance versus susceptibility of three-spined sticklebacks (Gasterosteus aculeatus) against infection with the eye-fluke (Diplostomum pseudospathacaeum), a parasite whose metacercariae are protected from the immune system within the eye lens. We predicted that in families with high susceptibility, the adaptive immune system would be upregulated when challenged with infection. In accordance, we found that MHC class IIB expression is increased by approximately 50% in those lines selected for higher parasite load (i.e. low innate response). This suggests extensive genetic correlations between innate and adaptive immune system and/or crosstalk between both lines of defense. An efficient, specific innate immune response might reduce overall activation of the immune system and potentially alleviate associated effects of immunopathology.     

Execution by lethal injection, euthanasia, organ-donation and the proper goals of medicine

In a recent issue of this journal, David Silver and Gerald Dworkin discuss the physicians' role in execution by lethal injection. Dworkin concludes that discussion by stating that, at that point, he is unable to think of an acceptable set of moral principles to support the view that it is illegitimate for physicians to participate in execution by lethal injection that would not rule out certain other plausible moral judgements, namely that euthanasia is under certain conditions legitimate and that organ-donation surgery is sometimes permissible. This article draws attention to some problems in the views of Silver and Dworkin and suggests moral principles which support the three moral views just mentioned.     

Otters and fish farms in the Sado estuary: ecological and socio-economic basis of a conflict

The degree of conflict between otter conservation and fish farming was assessed at Sado estuary (SW Portugal), using ecological (otter visiting rates to fish farms and consumption of commercial fish) and socio-economic (past and current instruments and policies addressing the conflict and a social impact assessment, including a discourse analysis of relevant stakeholders) parameters. The study concerned 14 fish farms producing Sparus aurata, Dicentrarchus labrax, Solea senegalensis and Solea solea. Results indicate high visiting rates in most fish farms (average: 76%), although in only 29%, species stocked were the most consumed prey. Other marine species and freshwater prey were the basis of otter diet in the remaining fish farms. The conflict is quite consensual among most fish farmers, and the results indicate that the perceived conflict by fish farmers has an ecological basis, although there are large gaps between effective and perceived predation. No specific instruments exist in Portugal to address the conflict, but some not specifically targeted can have an effect (e.g. species protection legislation and aquaculture licensing), although with limitations to effectively contribute to its mitigation (e.g. lack of enforcement and supervision). Formulating and assessing solutions is the following step, using a participatory approach to the development and evaluation of mitigation/compensation strategies, capable of providing an effective reconciliation of the conflict.

Colonization of freshwater habitats by an introduced crayfish, <Emphasis Type="Italic">Procambarus clarkii</Emphasis>, in Southwest Iberian Peninsula

The introduction of some crustacean species has produced alterations of freshwater environments and declines of native species worldwide. The red swamp crayfish, Procambarus clarkii Girard, was introduced in the Southwest Iberian Peninsula in the 1970’s, producing severe impacts on rice agriculture and on native biota such as macrophytes, gastropods, native crayfish and amphibians. We studied the distribution of P. clarkii in two areas of SW Iberian Peninsula: the Sado River basin (SW Portugal), an area colonized by this species around 1990, and the Parque Natural del Entorno de Doñana (SW Spain), colonized soon after its introduction in the Iberian Peninsula, in the 1970’s. Our main goal was to determine which factors limit crayfish distribution, which could help to identify the most effective management practices to contain its spread. Procambarus clarkii was found in most types of water bodies, including small and shallow ones. Distance to a crayfish source was the single predictor variable explaining crayfish occurrence in most types of habitats and in both areas. The only exception was for the Sado permanent stream points, where crayfish presence was negatively affected by an interaction between elevation and flow velocity. Other habitat characteristics have apparently little or no importance for its successful colonization. Moreover, this study indicated that overland dispersal is apparently a frequent phenomenon in this species. Our findings can be used to determine which habitats are most likely to be colonized by the crayfish and to develop practical measures which may limit its spread and minimize its impacts.     

Impact of climatic variability on parameters used in typology and ecological quality assessment of surface waters—implications on the Water Framework Directive

In most cases the negative impacts of climate change to aquatic ecosystems cannot be mitigated by measures in the river basin management. Ignoring climate change by the Water Framework Directive may have strong implications for the typology and quality assessment systems used for water bodies. As a result of climate change, water bodies, especially those located near the type boundaries may change their type. Compared to typology characteristics, water quality parameters are even more labile and may be easily affected by climate change. The paper exemplifies that the anticipated deterioration of water quality within the time frame relevant for WFD implementation may be large enough to endanger the fulfillment of the set water quality objectives. The review of the river basin characterization every six years, as required by the WFD, might also include re-evaluation of reference conditions according to the changes observed at pristine reference sites. As a consequence, the restoration targets (i.e., the good ecological status) would also need to be evaluated periodically.