On non-Eltonian methods of hunting Cladocera,or impacts of the introduction of planktivorous fish on zooplankton composition and clear-water phase occurrence in a Mediterranean reservoir |
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Authors: | Jaime Ordóñez Joan Armengol Enrique Moreno-Ostos Luciano Caputo Juan Carlos García Rafael Marcé |
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Institution: | 1.Fluvial Dynamics and Hydrological Engineering (FLUMEN), Department of Ecology,University of Barcelona,Barcelona,Spain;2.Department of Ecology and Geology,University of Málaga,Málaga,Spain;3.Aigües Ter-Llobregat. Ctra. Martorell a Olesa,Barcelona,Spain;4.Catalan Institute for Water Research (ICRA),Scientific and Technological Park of the University of Girona,Girona,Spain |
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Abstract: | Among the topics covered by Hutchinson’s Santa Rosalia article, the question of the shortening and lengthening of food webs
occupies a central role. As Hutchinson realized, at the time scales of ecological studies, the impact of invader species on
established food webs is the fastest shortcut to the shortening or lengthening of the food webs. The construction of thousands
of dams in Spain during the last century has offered ecologists a good opportunity to test the effects of invader fish species
on the plankton dynamics of these systems. In this article, a series of data related to the food web structure of Sau Reservoir
is analyzed for the period 1997–2005. Parameters such as Secchi depth and chlorophyll concentration, as well as abundance
and size structure of zooplankton, have been matched to the zooplankton dynamics in the reservoir. Most of the changes detected
within this period are attributed to the introduction of zooplanktivorous fish in the reservoir. The Secchi depth measurements
have showed a progressive diminution in the clear-water phase during recent years. These changes have been related to the
decrease in the abundance of Daphnia and to the reduction of the size of zooplankton, which help to explain concomitant increases in the chlorophyll concentration
in the same period. Other observed changes in the composition of the zooplankton community have been the substitution of Daphnia by Bosmina and the increase in the abundance of rotifers. Thus, the annual average abundance of Bosmina in 1997 was 70% of cladocerans, while in 2005 it reached 98%. In parallel, the percentage occurrence of individual rotifers
was 40% of total zooplankton numbers but had risen to 85% at the end of the period. All these changes are attributed to the
artificial expansion of the food web through stocking of the reservoir with zooplanktivorous fish (Rutilus rutilus and Alburnus alburnus). This study improves our understanding of the trophic relationships in the food web prior to the introduction of the fish. |
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