Long-term effects of planktivore removal: results from a manipulated and a reference lake

Sell, Anne F.; Hornig, Uwe; Benndorf, Jürgen

doi:10.1080/03680770.1995.11900823

Cited by 3 publications

(1 citation statement)

References 8 publications

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“…Margalef (1983) showed a certain tendency to favour the biomanipulation or the introduction of planktivorous fish species in reservoirs (e. g. Coregonus, Tilapia, Alburnus), as a means to control eutrophication. The fact is that this type of action may even be counterproductive, benefiting the development of phytoplankton even more by encouraging a zooplankton of smaller size with a less efficient filtering capacity (Köthe et al, 1997;Sell et al, 1997); however, there are some positive experiences in small and eutrophic water bodies (Straskraba et al, 1993). In addition, the introduction of exotic species of fish in general, as described below, may have extremely negative collateral effects, including the appearance of other undesirable species (ciliates, molluscs, etc.)…”

Section: Managing Reservoir Eutrophicationmentioning

confidence: 99%

Integrated environmental management of current reservoirs and regulated rivers

Ybars¹

2006

Limnetica

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At present, it is a common practice to identify reservoirs as the cause of negative effects on the regulated reaches of rivers. Reservoirs and regulated rivers maintain a close unidirectional relationship, downstream, so that the management of a reservoir, in addition to conditioning its own ecological characteristics, also determines the organization, operation and possibilities of the regulated river ecosystem. Within Spain, the four main environmental problems affecting the reservoir-regulated river system are the alteration of flow regimes, the eutrophication, the interruption of sediment transport and the increasing practice of introducing exotic species. It is possible to continue to draw an indefinite list of the concerns in measuring and criticizing the impacts of reservoirs on rivers, even proposing the demolition of dams, but it is also possible to think about the strategic value of reservoirs in guaranteeing availability of water and the preservation of the standards of living obtained as a result, and to therefore promote an environmental management program to reduce the negative impacts upon the rivers. The options for controlling levels and flows offered by almost any dam, together with the inclusion in the operating program of each reservoir of a set of environmental goals for the reservoir itself and for the downstream regulated river, is an area of application within limnology which has not been as propagated as it should have been. Many myths have still to be demolished -although perhaps no as many as there are dams proposed-and there is considerable margin for the improvement of regulated rivers. The environmental management options can not be tackled in one single paper, and therefore our aim here is to merely offer a series of basic reflections from which an environmental management approach of the reservoirs might be drawn up, and can be integrated with the uses for which they were built and with current social demands concerning the conservation of continental aquatic ecosystems.

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Section: Managing Reservoir Eutrophicationmentioning

confidence: 99%

Integrated environmental management of current reservoirs and regulated rivers

Ybars¹

2006

Limnetica

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Morphological defenses induced in situ by the invertebrate predator Chaoborus: comparison of responses between Daphnia pulex and D. rosea

Sell

2000

Oecologia

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The presence of plankton predators may induce altered morphology in their potential prey. To date, the mechanism of induction and adaptive value of such defensive responses have been examined in the laboratory. This study investigated the morphological defense structures induced by the invertebrate predator Chaoborus in two coexisting Daphnia species, D. pulex and D. rosea, in the field. In Piscivore Lake (Gräfenhain, Germany), continuous and intense biomanipulation had led to near elimination of planktivorous fish and greatly increased abundances of Chaoborus (up to >10 larvae l). Here, the density of Chaoborus was manipulated within the lake by an enclosure/exclosure setup and resulting morphological responses of Daphnia spp. were investigated in situ. Three replicate enclosures (4.6 m) contained no Chaoborus (predator exclusion bags), whereas Chaoborus entered three others at ambient densities (predator enclosures). In both species of Daphnia, formation of neckteeth and elongation of the tail spine were recorded in the predator enclosures, but not in the predator exclusion treatments. Additionally, D. rosea responded to predator inclusion with an increase of the size at first reproduction. Despite the induced defense structures, the presence of Chaoborus caused increased mortality of both Daphnia species. In addition, Chaoborus affected the coexistence of the two populations of Daphnia by causing higher relative mortality in D. rosea. Neckteeth formation was always more pronounced in D. pulex than in D. rosea of the same size. Neckteeth were induced specifically in vulnerably sized juvenile instars of D. pulex, but were not found in all vulnerable instars of D. rosea. In D. rosea, neckteeth were few or absent in the ephippial hatchlings, and neckteeth formation ceased before juveniles reached a body size outside the range that larger larval stages of Chaoborus could ingest. This study provides the first experimental demonstration in the field of the inducibility of morphological defense structures in Daphnia at ambient densities of Chaoborus larvae, and quantifies these in situ responses. This expands on earlier observations of a correlation between predator density in the field and the expression of neckteeth in Daphnia. The term "maximum size for neckteeth formation" (MSNF) is defined as the limit in body size above which no production of neckteeth was evident. This limit was used to distinguish the size classes of Daphnia that show a sensitive response to Chaoborus kairomone. This new term may be used for further comparisons among species and among different types of predator-induced responses as well as for the evaluation of the adaptive value of defense structures.

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Low Genotypic Diversity in a Daphnia Pulex Population in a Biomanipulated Lake: The Lack of Vertical and Seasonal Variability

Matthes

2004

Hydrobiologia

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Long-term effects of planktivore removal: results from a manipulated and a reference lake

Cited by 3 publications

References 8 publications

Integrated environmental management of current reservoirs and regulated rivers

Integrated environmental management of current reservoirs and regulated rivers

Morphological defenses induced in situ by the invertebrate predator Chaoborus: comparison of responses between Daphnia pulex and D. rosea

Low Genotypic Diversity in a Daphnia Pulex Population in a Biomanipulated Lake: The Lack of Vertical and Seasonal Variability

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