Global Decline of and Threats to Aegagropila linnaei, with Special Reference to the Lake Ball Habit

The freshwater macroalga Aegagropila linnaei can occur attached or unattached, but is best known for its free-floating spherical growth form ("lake balls," "Cladophora balls," or "marimo"). The worldwide distribution of this species was reconstructed using more than 1200 specimens from 28 herbaria, air extensive literature survey, and field observations. Aegagropila linnaei was found in 283 locations, with the majority located in central and northern Europe. Felt, records of A. linnaei exist from North America, but it is relatively widespread III Japan. The preferred habitat is inferred to be oligomesotrophic lakes with moderate to high calcium levels. In more than 50% of the known locations, A. linnaei has not been found in the last 30 years, and this decline is assumed to be correlated with changes in trophic conditions ill those lakes. The unttached growth forms show a stronger decline than attached populations as a result of the habitat types in which they can occur.status: publishe

La dynamique de la pratique sportive des jeunes

Numéro thématique : 'Sport et activité physique : vie personnelle, sociale et économique'. Enquête réalisée auprès de jeunes sportifs de deux villes de la région parisienne. Passion pour le sport, investissement dans l'activité sportive, réalisation d'une vocation sportive comme résultats de compromis entre plusieurs logiques relationnelles hétérogènes : priorités éducatives de la famille, rôle des camarades ..

Fighting internal phosphorus loading: An evaluation of the large scale application of gradual Fe-addition to a shallow peat lake

Abatement of external phosphorus (P) loading and biomanipulation are measures that are often applied with the aim to restore a macrophyte dominated clearwater state in turbid, anthropogenically eutrophied lakes. The recovery of such lakes, however, is often hampered by ‘internal eutrophication’, as a result of the release of historically accumulated P from the sediment into the water column. One way to combat this internal P loading is by adding iron (Fe) into the lake, which naturally binds to phosphate. Although studied in the laboratory or mesocosms, the effects of iron addition on a whole-lake scale are largely unknown. In this study we therefore compiled lake monitoring data to evaluate the effect of a gradual dose of 33 g Fe m2 on the water quality and biotic communities (phytoplankton, zooplankton and macrophytes) of Lake Terra Nova. During and after the Fe-addition, we also carried out assays to evaluate the effect of the Fe-addition on sediment P-release rates. Lake Terra Nova is a eutrophied, shallow peaty lake that has been subjected to biomanipulation measures for 10 years. The large scale addition of iron during 2010 and 2011 resulted in a substantial reduction of dissolved P, suspended matter (SM), phytoplankton biomass and relative Cyanobacterial biomass, whereas macrophytes reappeared. Fe-addition also resulted in strongly reduced sediment P-mobilisation rates. Nevertheless, reductions of water column TP in response to the Fe-addition were short-lived. This discrepancy between the observed TP-levels in the water column and sediment P-release rates could indicate that sustained loading with external P and interactions of chemical compounds with Fe may jeopardize long term restoration success by depleting the water column reservoir of reactive Fe. Ecological processes can in addition enhance this process by shunting P from the sediment to the water column

Invasive crayfish threaten the development of submerged macrophytes in lake restoration.

Submerged macrophytes enhance water transparency and aquatic biodiversity in shallow water ecosystems. Therefore, the return of submerged macrophytes is the target of many lake restoration projects. However, at present, north-western European aquatic ecosystems are increasingly invaded by omnivorous exotic crayfish. We hypothesize that invasive crayfish pose a novel constraint on the regeneration of submerged macrophytes in restored lakes and may jeopardize restoration efforts. We experimentally investigated whether the invasive crayfish (Procambarus clarkii Girard) affects submerged macrophyte development in a Dutch peat lake where these crayfish are expanding rapidly. Seemingly favourable abiotic conditions for macrophyte growth existed in two 0.5 ha lake enclosures, which provided shelter and reduced turbidity, and in one lake enclosure iron was added to reduce internal nutrient loading, but macrophytes did not emerge. We transplanted three submerged macrophyte species in a full factorial exclosure experiment, where we separated the effect of crayfish from large vertebrates using different mesh sizes combined with a caging treatment stocked with crayfish only. The three transplanted macrophytes grew rapidly when protected from grazing in both lake enclosures, demonstrating that abiotic conditions for growth were suitable. Crayfish strongly reduced biomass and survival of all three macrophyte species while waterfowl and fish had no additive effects. Gut contents showed that crayfish were mostly carnivorous, but also consumed macrophytes. We show that P. clarkii strongly inhibit macrophyte development once favourable abiotic conditions for macrophyte growth are restored. Therefore, expansion of invasive crayfish poses a novel threat to the restoration of shallow water bodies in north-western Europe. Prevention of introduction and spread of crayfish is urgent, as management of invasive crayfish populations is very difficult

Biomass and survival of transplanted macrophytes under different grazing treatments.

<p>Mean biomass (left panels) and survival (right panels) of <i>C. virgata</i> (A,B), <i>E. nuttallii</i> (C,D), and <i>M. spicatum</i> (E,F) transplants at the end of the experiment for the non-iron and iron pond. Different letters or numbers in biomass panels indicate significant differences between treatments for the iron pond and non-iron pond respectively (Tukey post hoc comparisons, <i>P</i><0.050). Significant differences in transplant biomass between ponds within a single treatment were found for <i>Elodea</i> biomass in the partial exclosure and for <i>Myriophyllum</i> biomass in the full exclosure and are indicated by asterisks (Tukey post-hoc comparisons, * <i>P</i><0.050; ** <i>P</i><0.01; ***<i>P</i><0.001). For the survival panels, different letters indicate significant differences between treatments only. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078579#pone-0078579-t003" target="_blank">Table 3</a> for results of the statistical analyses.</p

Iron addition as a shallow lake restoration measure: impacts on charophyte growth

Eutrophication has caused a decline of charophyte species in many shallow lakes in Europe. Even though external inputs of phosphorus are declining, internal loading of P from the sediment seems to delay the recovery of these systems. Iron is a useful chemical binding agent to combat internal phosphorus loading. However, the effects of iron addition on charophytes are not yet known. In this study we experimentally tested the potential toxicity of iron(III)chloride (FeCl3) on two different charophytes, Chara virgata Kützing and Chara globularis Thuiller added at the concentration of 20 g Fe m−2 and 40 g Fe m−2 to the surface water. C. virgata growth was not significantly affected, whereas C. globularis growth significantly decreased with increasing iron concentrations. Nonetheless, biomass of both species increased in all treatments relative to starting conditions. The decrease of C. globularis biomass with high iron additions may have been caused by a drop in pH and alkalinity in combination with iron induced light limitation. Iron addition over a longer time scale, however, will not cause this rapid drop in pH. Therefore, we conclude that adding iron(III)chloride in these amounts to the surface water of a lake can potentially be a useful restoration method.

Reversal in competitive dominance of a toxic versus non-toxic cyanobacterium in response to rising CO2

Climate change scenarios predict a doubling of the atmospheric CO2 concentration by the end of this century. Yet, how rising CO2 will affect the species composition of aquatic microbial communities is still largely an open question. In this study, we develop a resource competition model to investigate competition for dissolved inorganic carbon in dense algal blooms. The model predicts how dynamic changes in carbon chemistry, pH and light conditions during bloom development feed back on competing phytoplankton species. We test the model predictions in chemostat experiments with monocultures and mixtures of a toxic and non-toxic strain of the freshwater cyanobacterium Microcystis aeruginosa. The toxic strain was able to reduce dissolved CO2 to lower concentrations than the non-toxic strain, and became dominant in competition at low CO2 levels. Conversely, the non-toxic strain could grow at lower light levels, and became dominant in competition at high CO2 levels but low light availability. The model captured the observed reversal in competitive dominance, and was quantitatively in good agreement with the results of the competition experiments. To assess whether microcystins might have a role in this reversal of competitive dominance, we performed further competition experiments with the wild-type strain M. aeruginosa PCC 7806 and its mcyB mutant impaired in microcystin production. The microcystin-producing wild type had a strong selective advantage at low CO2 levels but not at high CO2 levels. Our results thus demonstrate both in theory and experiment that rising CO2 levels can alter the community composition and toxicity of harmful algal blooms.