Modèles ecologiques pour l'extrapolation des effets écotoxicologiques enregistrés lors de biotests in situ cheZ Gammarus

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCAInternational audienceEvaluating the effects of chemical contamination on populations and ecological communities still constitutes a challenging necessity in environmental management. However the toxic effects of contaminants are commonly measured by means of organism-level responses. Linking such effects measures with ecological models is a promising way to apprehend population-level impacts. In this way, population models are currently increasingly used in predictive risk assessment procedures, but their use in environmental diagnostic framework remains limited due to their lack of ecological realism. The present study with the crustacean amphipod Gammarus fossarum, a sentinel species in freshwater monitoring, combines a dual field and laboratory experimental approach with a population modelling framework. In this way, we developed an ecologically-relevant periodic matrix population model for Gammarus. This model allowed us to capture the population dynamics in the field, and to understand the particular pattern of demographic sensitivities induced by Gammarus life-history phenology. The model we developed provided a robust population-level assessment of in situ-based effects measures recorded during a biomonitoring program on a French watershed impacted by past mining activities. Thus, our study illustrates the potential of population modelling when seeking to decipher the role of environmental toxic contamination in ecological perturbations

Amphipod susceptibility to metals: Cautionary tales

Heavy metals accumulated by aquatic crustaceans in environmental studies are normally investigated using the whole body burden, with little regard paid to uptake in different tissues, to potential gender of life stage differences, or to the influence of nutrition on the test organism. This is likely to give erroneous conclusions for a dose–response relationship within the toxicity test and potentially lead to wrong conclusions for the ecological risks of metals where species may have higher sensitivities with gender and life stage than indicated or that functionally metals may be sequestered into parts of the body so are not bioavailable. This could lead to under-estimation or over-estimation of the toxicity of metals,respectively, inaccuracy of metal budget calculations and evaluation of trophic transfers of metals. This study evaluated the influences of life stage, gender, and a priori nutritional state in the uptake of the metals zinc (an essential micro-nutrient; Zn) and cadmium (a non-essential element; Cd) in the amphipod Echinogammarus marinus. The study showed that life stage, and nutritional stage did significantly influence the uptake and bioaccumulation for both metals, but only Cd showed differential uptake and bioaccumulation with gender. In addition, it was concluded that there was a significant uptake and accumulation of both metals within the exoskeleton of the amphipods, which though adding to the full body burden would add little to toxicity through lack of bioavailability. These results showed that care should be taken when interpreting results from tests normally preformed on such test organisms

Differences in stress tolerance and brood size between a non-indigenous and an indigenous gammarid in the northern Baltic Sea

Differences in stress tolerance and reproductive traits may drive the competitive hierarchy between nonindigenous and indigenous species and turn the former ones into successful invaders. In the northern Baltic Sea, the non-indigenous Gammarus tigrinus is a recent invader of littoral ecosystems and now occupies comparable ecological niches as the indigenous G. zaddachi. In laboratory experiments on specimens collected between June and August 2009 around Tva¨rminne in southern Finland (59°500N/23°150E), the tolerances towards heat stress and hypoxia were determined for the two species using lethal time, LT50, as response variable. The brood size of the two species was also studied and some observations were made on maturation of juveniles. Gammarus tigrinus was more resistant to hypoxia and survived at higher temperatures than G. zaddachi. Brood size was also greater in G. tigrinus than in G. zaddachi and G. tigrinus matured at a smaller size and earlier than G. zaddachi. Hence, there are clear competitive advantages for the non-indigenous G. tigrinus compared to the indigenous G. zaddachi, and these may be further strengthened through ongoing environmental changes related to increased eutrophication and a warming climate in the Baltic Sea region

INTERACTION BETWEEN NATIVE AND ALIEN SPECIES OF CRAYFISH IN AUSTRIA: CASE STUDIES

In Austria, three indigenous crayfish species occur: the noble crayfish (Astacus astacus), the stone crayfish (Austropotamobius torrentium), and the white-clawed crayfish (Austropotamobius pallipes). It is not known if Astacus leptodactylus is autochthonous in the very eastern part of Austria, near the border with Hungary and Slovakia. In other parts of Austria the Turkish crayfish has been transplanted into several gravel pits and ponds. Up to now, the red swamp crayfish (Procambarus clarkii) is not known to occur in the wild, but can be bought alive in fish markets, restaurants, and the aquarium trade. The Nearctic spiny-cheek crayfish (Orconectes limosus) and the signal crayfish (Pacifastacus leniusculus) have been introduced since the 1970s by crayfish farmers because these species are resistant to the crayfish plague fungus (Aphanomyces astaci). There are just a few populations of O. limosus, and the species is not spreading actively. However, P. leniusculus is widespread all over Austria, and was illegally introduced from one water body to another. It can be characterized as an aggressive, invasive North American species, spreading actively and acting as a vector of the crayfish plague. Unfortunately the habitat requirements of the native noble crayfish and the alien signal crayfish are nearly the same. Case studies are given in the following chapters: the first group of examples refers to water bodies where the alien signal crayfish is most probably the cause of displacement of the indigenous noble crayfish: 1) Hintersee, 2) Irrsee (« Zeller See »), 3) north-western Lower Austria (« Waldviertel »), 4) Merzenstein (aquacultural enterprise), 5) Neufelder See. The second group of examples refers to water bodies where alien and indigenous species are able to coexist: a) the confluence of the main course of the Danube River, the Ölhafen and the Neue Donau in the southeast part of Vienna, b) the Schönauer Wasser, a backwater of the Danube River downstream Vienna, c) backwaters and ox bows of the Morava River. The differences between these two groups are analysed, and it is speculated on possible causes allowing coexistence. Some conclusions are drawn. Important actions related to the protection of native crayfish are briefly discussed

ROUNDTABLE SESSION 2: DOES LEGISLATION WORK IN PROTECTING VULNERABLE SPECIES?

As a result of discussions held at the Innsbruck CRAYNET meeting and the answers given to a subsequent questionnaire sent out to the National Co-ordinators of the 11 countries/regions, it is clear that most European countries aim at trying to protect their indigenous crayfish species (ICS) from overexploitation, habitat modification, pollution, and spread of non-indigenous crayfish species (NICS) and crayfish plague. Two detailed case studies are given for Austria and England plus a summary of the questionnaires. These clearly illustrate the different attitudes of countries to protecting and managing their ICS and NICS. The situation is highly complex and differs depending upon whether or not there is a tradition for eating crayfish. Consequently, harmonisation of national and regional regulations for ICS and NICS in Europe may not be possible in the short term. In many cases legislation has not prevented further destruction of populations of ICS and the spread of NICS. However, without such legislation the situation could have been a lot worse and some ICS could already have become critically endangered. The continued efforts by the crayfish community and national authorities have resulted in a scenario where there are still some countries without NICS, and in most European countries there are specific areas with numerous, viable populations of ICS that are considered valuable and are protected by the authorities as well as by local people. The situation has recently been improved by providing protection for Austropotamobius torrentium under Annex II of the EU Habitats Directive. A major objective must be to develop methods for eradicating nuisance populations of NICS before they spread any further

AUSTROPOTAMOBIUS TORRENTIUM AS AN INDICATOR FOR HABITAT QUALITY IN RUNNING WATERS?

In the present study we tried to quantify the indication value of A. torrentium referring to habitat quality. This variable is expressed as the availability of appropriate refuge stones on the bottom and banks of running waters. The brooks occupied by the indigenous stone crayfish in Lower Austria show a high variability in the current velocity and substrate heterogeneity. Having some experience in hand searching we assumed that the distribution pattern of the crayfish on the stream bed is strongly correlated with the distribution of cobble and pebbles within a certain grain size. The aim of our study was to quantify the dependence of the shelter requirements for A. torrentium on grain size and water velocity, as well as the seasonal mobility of the crayfish. Shelters where velocity exceeded 25 cm s-1 were not occupied. Pebbles with a bearing surface greater than 300 cm2 were preferred, and the probability of crayfish occupation rose quickly as the stone’s bearing surface increased up to 900 cm2. Most individuals changed their location only a few meters (median 4 m). The distance from the point of first capture increased only little within the length of time passed until re-capture, suggesting a conservative use of space