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Vanderstukken M.,CNRS Biology of Aquatic Organisms and Ecosystems Laboratory | van Colen W.,CNRS Biology of Aquatic Organisms and Ecosystems Laboratory | Declerck S.A.J.,Laboratory of Aquatic Ecology and Evolutionary Biology | Declerck S.A.J.,Netherlands Institute of Ecology | Muylaert K.,CNRS Biology of Aquatic Organisms and Ecosystems Laboratory
Freshwater Biology | Year: 2011

In temperate regions, submerged macrophytes can hamper phytoplankton blooms. Such an effect could arise directly, for instance via allelopathy, or indirectly, via competition for nutrients or the positive interaction between submerged macrophytes and zooplankton grazing. However, there is some evidence that the positive interaction between submerged macrophytes and zooplankton grazing is less marked in warmer regions, where the interaction is less well studied, and that negative effects of higher water plants on phytoplankton biomass are weaker. We carried out two consecutive mesocosm experiments in Uruguay (subtropical South America) to study the effects of two common submerged macrophytes from this region (Egeria densa and Potamogeton illinoensis) on phytoplankton biomass, in the absence of zooplankton grazing. We compared phytoplankton development between different macrophyte treatments (no macrophytes, artificial macrophytes, real Egeria and real Potamogeton). We used artificial macrophytes to differentiate between physical effects (i.e. shading, sedimentation and competition with periphyton) and biological effects (i.e. nutrient competition and allelopathy). In Experiment 1, we found no evidence for physical effects of macrophytes on phytoplankton biomass, but both macrophyte species seemed to exert strong biological effects on phytoplankton biomass. Only Egeria affected phytoplankton community structure, particularly tempering the dominance of Scenedesmus. Nutrient addition assays revealed that only Egeria suppressed phytoplankton through nutrient competition. We performed a second mesocosm experiment with the same design, but applying saturating nutrient conditions as a way of excluding the effects of competition for nutrients. This experiment showed that both macrophytes were still able to suppress phytoplankton through biological mechanisms, providing evidence for allelopathic effects. Our results indicate that both common macrophytes are able to keep phytoplankton biomass low, even in the absence of zooplankton grazing. © 2011 Blackwell Publishing Ltd. Source


Cao Quoc N.,Can Tho University | Vromant N.,Vlaamse Vereniging voor Ontwikkelingssamenwerking en Technische Bijstand | Le Thanh D.,Can Tho University | Ollevier F.,Laboratory of Aquatic Ecology and Evolutionary Biology
Aquaculture International | Year: 2012

In recent years, a rotational system consisting of two rice crops followed by a fish pen culture during the monsoon flood period was adopted in parts of the flood-prone region of the Mekong Delta. In this paper, we use the survey data from 51 fish pen farmers at Co Do and Vinh Thanh district, Can Tho City, to investigate the factors affecting fish yield and profit in such fish pen culture system. The net yield of all stocked fish varies from 377 to 3,782 kg/ha/crop while the return above variable costs varies from -5.3 to 9.8 million VND/ha/crop. Low fish price at harvest and the difficulty to sell below market sized fish at a period of oversupply are the main problems for fish pen culture. Fish net yield significantly increases with stocking density and is linked with specific polycultures. Common carp and bighead carp perform best in fish pen culture, both in production and profit considerations. Harvest body mass of common carp is mainly limited by increasing common carp stocking density. Therefore, a stocking density of common carp of about 6,000 fish/ha is recommended to obtain the optimum combination of reasonable body masses, and a good price, as well as a high return above fingerling costs. © 2012 Springer Science+Business Media B.V. Source


Declerck S.A.J.,Netherlands Institute of Ecology | Declerck S.A.J.,University of British Columbia | Declerck S.A.J.,Laboratory of Aquatic Ecology and Evolutionary Biology | Winter C.,University of British Columbia | And 6 more authors.
ISME Journal | Year: 2013

Dispersal limitation is generally considered to have little influence on the spatial structure of biodiversity in microbial metacommunities. This notion derives mainly from the analysis of spatial patterns in the field, but experimental tests of dispersal limitation using natural communities are rare for prokaryotes and, to our knowledge, non-existent for viruses. We studied the effects of dispersal intensity (three levels) and patch heterogeneity (two levels) on the structure of replicate experimental metacommunities of bacteria and viruses using outdoor mesocosms with plankton communities from natural ponds and lakes. Low levels of dispersal resulted in a decrease in the compositional differences (beta diversity) among the communities of both bacteria and viruses, but we found no effects of patch heterogeneity. The reductions in beta diversity are unlikely to be a result of mass effects and only partly explained by indirect dispersal-mediated interactions with phytoplankton and zooplankton. Our results suggest that even a very limited exchange among local communities can alter the trajectory of bacterial and viral communities at small temporal and spatial scales. © 2013 International Society for Microbial Ecology. All rights reserved. Source


Karl I.,University of Greifswald | Stoks R.,Laboratory of Aquatic Ecology and Evolutionary Biology | De Block M.,Laboratory of Aquatic Ecology and Evolutionary Biology | Janowitz S.A.,University of Greifswald | Fischer K.,University of Greifswald
Global Change Biology | Year: 2011

Global warming and its associated increase in temperature extremes pose a substantial challenge on natural systems. Tropical ectotherms, living close to their (upper) critical thermal limits, may be particularly vulnerable to global warming, yet they are as a group understudied. Most studies assessing fitness effects under global warming focused on life-history correlates such as body size and largely neglected immune function. Furthermore they did not consider to what extent temperature effects may be modulated under resource-based trade-offs. Against this background we here investigate effects of temperature extremes on fitness-related adult traits (viz. body mass, fat content, and two key parameters of arthropod immune function: phenoloxidase (PO) activity and haemocyte numbers) at different levels of larval and adult food stress in the tropical butterfly Bicyclus anynana. Body mass and PO activity decreased after short-term larval food stress, but not fat content and haemocyte numbers (probably owing to compensatory mechanisms during further development). Longer-term food deprivation in the adult stage, in contrast, diminished performance throughout, confirming that the feeding treatments chosen imposed stress. Temperature manipulations yielded contrary responses between life-history correlates and immune function: while body mass and fat content increased by increasing temperatures, PO activity and haemocyte numbers decreased. The latter was particularly pronounced under adult food stress, suggesting a resource-allocation trade-off. Our data suggest that global warming will not only reduce performance through direct effects of thermal stress, but also through secondary effects on adult immune function, which may be missed when exclusively focussing on other life-history correlates. © 2010 Blackwell Publishing Ltd. Source


Jocque M.,Laboratory of Aquatic Ecology and Evolutionary Biology | Jocque M.,Bulgarian Academy of Science | Vanschoenwinkel B.,Laboratory of Aquatic Ecology and Evolutionary Biology | Brendonck L.,Laboratory of Aquatic Ecology and Evolutionary Biology
Freshwater Biology | Year: 2010

In the light of the recent surge of interest in small and often temporary wetlands as model systems for ecological and evolutionary research, this article reviews current knowledge on freshwater rock pools and their fauna. Freshwater rock pools occur all over the globe in all major biomes and depend mainly on precipitation for filling. Rock pool clusters are some of the more persistent and oldest freshwater habitats worldwide. Interactions between climate and geology (e.g. limestone, sandstone, granite) generally determine the morphology and hydrology of rock pool habitats, with hydroperiods ranging from several days up to the whole year. Pool volume is usually small, resulting in strongly fluctuating environmental conditions, low conductivity and wide variations in pH (from 4.0 to 11.0) and temperature (from freezing point to 40 °C) often with well-marked diel cycles. The highly variable environmental conditions, combined with the unpredictability of the flooding regime, require high stress tolerance of the inhabitants, with adaptations for surviving the dry phase such as the production of resistant stages and active emigration followed by recolonisation. About 460 aquatic animal species have been recorded from freshwater rock pools around the world. Approximately 170 of these are passive dispersers, which mainly disperse as resting stages via wind and overflow of water between pools. Successful long distance dispersal seems limited. This group is composed mainly of rock pool specialists with a high degree of endemicity. The remaining taxa can be considered active dispersers, with migration usually restricted to the adult stage. Often these taxa are broadly distributed and occur in a wide range of temporary habitats in addition to rock pools. The inherent characteristics of freshwater rock pools, such as their simple structure and occurrence on similar substrata all over the world, facilitate comparison of research results and promote rock pools as model systems for ecological and evolutionary research. Nevertheless, despite their potential as model systems, the unique fauna and their importance as sources of freshwater in dry countries, the ecology of freshwater rock pools remain virtually unexplored in large parts of the world. © 2010 Blackwell Publishing Ltd. Source

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