Copernicus Marine Service ocean state report, issue 4

This is the final version. Available from Taylor & Francis via the DOI in this record. FCT/MCTE

Biological diversity of epibenthic invertebrates in relation to environmental factors in lava caves around Lake Mývatn (N-E Iceland)

Biodiversity, and its understanding and maintenance, are nowadays concerns in many fields of sciences. In freshwater, epibenthic invertebrates are important for their environment as consumers at intermediate trophic level and as food resources for other organisms. Their sensitivity to environmental conditions, influencing their biotic diversity and abundance, make them good indicators of the health of freshwater ecosystems. In the vicinity of Lake Mývatn (NE Iceland), numerous groundwater fed lava caves are found; they were formed after the collapse of lava tumuli. Groundwater seeps into the caves through porous lava bedrock, creating small ponds inhabited by Arctic charr and diverse invertebrates. The unique geomorphology of the caves creates various habitats, and along with that the potential for different invertebrate communities. In summer 2014, I sampled epibenthic crustaceans in 18 caves distributed in two areas around Lake Mývatn, Haganes and Vindbelgjar, along with measurements of environmental variables and geomorphology of the caves. I also sampled along a transect in four particular caves, to look at the changes in the diversity in relation to a light gradient. The main differences between Haganes and Vindbelgjar were observed with the environmental factors, which vary between the areas. Overall I found a low diversity of invertebrates in all lava caves although this diversity varied within and between areas. Some similarities in invertebrate composition were observed between the caves and the nearby Lake Mývatn. I found that the abundance of invertebrates per cave and per taxa decreased as light intensity decreased (i.e. going from the shore into the caves). Other than for light gradients, no clear correlations between environmental factors and invertebrate diversity was found. This study showed that even at small scale an ecosystem can be variable, and show differences. This is important for future studies and futures conservational ecology plans, not only for the caves, nor for Iceland, but worldwide.Skilningur á því hvernig líffræðileg fjölbreytni verður til og hvernig henni er viðhaldið er viðfangsefni fjölmargra vísindagreina. Hryggleysingjar sem lifa rétt fyrir ofan botninn, í ferskvatnskerfum, eru mikilvægir sem afræningjar á neðri þrepum fæðuvefja og sem fæða fyrir aðrar líferur. Þessar lífverur eru viðkvæmar fyrir umhverfisbreytingum, hafa áhrif á fjölbreytileika þeirra og þéttleika, sem gerir þær að góðum tækjum til að meta hnignun ferskvatnskerfa. Í kringum Mývatn má finna fjölmarga hraunhella sem fylltir eru af grunnvatni. Hellarnir urðu aðgengilegir þegar hellisþök hrundu, grunnvatn hefur streymt inn í hellana í gegnum gegndræp hraun. Þannig hefur myndast lítil tjörn í hverjum helli. Í tjörninni má finna bleikju auk fjölmargra tegunda hryggleysingja. Hellarnir eru fjölbreyttir að gerð og mynda ólík búsvæði fyrir þessar lífverur. Sumarið 2014 safnaði ég krabbadýrum yfir botni í átján hellum frá tveimur svæðum við Mývatn, Haganes og Vindbelgjar. Auk þess mældi ég umhverfisbreytur og lagði mat á útlitsbreytileika hellana. Auk þessa þá tók ég sýni á sniði í fjórum hellum, þar sem að skoðaðar voru breytingar í fjölbreytileika í tengslum við minnkandi ljós. Helsti munur í smádýrasamsetningu milli hella tengdist muni milli svæðana tveggja, Haganes og Vindbelgjar. Niðurstöðurnar sýndu að smádýrasamfélögin voru einföld, en þó var munur milli hella og svæða. Greina mátti að smádýrasamfélögin voru að einhverju leiti lík þeim sem finna má í Mývatni. Eftir því sem innar dró í hellana fækkaði bæði tegundum smádýra og fjölda þeirra. Aðrir þættir umhverfisþættir, en breytileiki í ljósi, sýndu bein tengsl við fjölbreytileika hryggleysingja. Rannsóknin sýndi að jafnvel á smáum skala má sjá fjölbreytileika í vistkerfum. Þetta er mikivæg þekking fyrir vistfræðilega nálgun á friðun, ekki bara fyrir hellana, eða Ísland, heldur á heimsvísu

Physiological and pathological changes in the eastern oyster Crassostrea virginica infested with the trematode Bucephalus sp. and exposed to the toxic dinoflagellate Alexandrium fundyense

© 2015 Elsevier Inc. Effects of experimental exposure to Alexandrium fundyense, a Paralytic Shellfish Toxin (PST) producer known to affect bivalve physiological condition, upon eastern oysters, Crassostrea virginica with a variable natural infestation of the digenetic trematode Bucephalus sp. were determined.After a three-week exposure to cultured A. fundyense or to a control algal treatment with a non-toxic dinoflagellate, adult oysters were assessed for a suite of variables: histopathological condition, hematological variables (total and differential hemocyte counts, morphology), hemocyte functions (Reactive Oxygen Species (ROS) production and mitochondrial membrane potential), and expression in gills of genes involved in immune responses and cellular protection (MnSOD, CAT, GPX, MT-IV, galectin CvGal) or suspected to be (Dominin, Segon).By comparing individual oysters infested heavily with Bucephalus sp. and uninfested individuals, we found altered gonad and digestive gland tissue and an inflammatory response (increased hemocyte concentration in circulating hemolymph and hemocyte infiltrations in tissues) associated with trematode infestation. Exposure to A. fundyense led to a higher weighted prevalence of infection by the protozoan parasite Perkinsus marinus, responsible for Dermo disease. Additionally, exposure to A. fundyense in trematode-infested oysters was associated with the highest prevalence of P. marinus infection. These observations suggest that the development of P. marinus infection was advanced by A. fundyense exposure, and that, in trematode-infested oysters, P. marinus risk of infection was higher when exposed to A. fundyense. These effects were associated with suppression of the inflammatory response to trematode infestation by A. fundyense exposure. Additionally, the combination of trematode infestation and A. fundyense exposure caused degeneration of adductor muscle fibers, suggesting alteration of valve movements and catch state, which could increase susceptibility to predation. Altogether, these results suggest that exposure of trematode-infested oysters to A. fundyense can lead to overall physiological weakness that decrease oyster defense mechanisms

Integrability of the one dimensional Schrödinger equation

International audienceWe present a definition of integrability for the one-dimensional Schrödinger equation, which encompasses all known integrable systems, i.e., systems for which the spectrum can be explicitly computed. For this, we introduce the class of rigid functions, built as Liouvillian functions, but containing all solutions of rigid differential operators in the sense of Katz, and a notion of natural of boundary conditions. We then make a complete classification of rational integrable potentials. Many new integrable cases are found, some of them physically interesting

Regards comparatistes sur la réforme belge du droit de la responsabilité extra-contractuelle: quelques suggestions pour le législateur et le juge (Groupe de recherche Grotius-Pothier)

Coherent privaatrech

Regards comparatistes sur la réforme belge du droit de la responsabilité extra-contractuelle : quelques suggestions pour le législateur et le juge (Groupe Grotius Pothier)

Coherent privaatrech

Symbolic Computations of First Integrals for Polynomial Vector Fields

International audienceIn this article, we show how to generalize to the Darbouxian, Liouvillian and Riccati case the extactic curve introduced by J. Pereira. With this approach, we get new algorithms for computing, if it exists, a rational, Darbouxian, Liouvillian orRiccati first integral with bounded degree of a polynomial planar vector field. We give probabilistic and deterministic algorithms. The arithmetic complexity of our probabilistic algorithm is in O (N omega+1), where N is the bound on the degree of a representation of the first integral and omega epsilon [2; 3] is the exponent of linear algebra. This result improves previous algorithms. Our algorithms have been implemented in Maple and are available on the authors' websites. In the last section, we give some examples showing the efficiency of these algorithms