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Factors controlling planktonic size spectral responses to autumnal circulation in a Mediterranean lake

AuthorsÁlvarez Cobelas, Miguel ; Rojo, Carmen; Velasco, José Luis ; Baltanás, Ángel
KeywordsCascading effect
Factor interaction
Food webs
Mixing depth
Physical forcing
Issue Date2006
PublisherBlackwell Publishing
CitationFreshwater Biology 51: 131-143 (2006)
Abstract1. Studies of planktonic size spectra have been common in recent years, but few concerning the effects of autumnal lake processes on those distributions have been reported. We carried out such a study for 93 days during early circulation in a small, mesotrophic, seepage lake with only benthivorous fish. Two distinct mixing periods occurred before full circulation in Las Madres lake (Spain). As a proxy of overall planktonic- and phytoplanktonic size distributions, the shape of a Pareto I power function was traced over time. The phytoplanktonic size spectrum was also used to test the hypothesis that phytoplankton might show a trophic cascade during early circulation. 2. Our results demonstrated that the overall size spectrum changed smoothly during the autumnal mixing, with sequential changes controlled by a combination of biotic and abiotic variables, albeit experiencing different temporal delays, always shorter than a week. A first combined, autogenic process, driven both by algal competition and a crustacean trophic effect, and a second physical-forcing process, driven by the combined effect of convective cooling and decreasing irradiance on mixed layer dynamics, may be related to the overall planktonic spectrum in the first and second periods of mixing, respectively. 3. The phytoplanktonic size spectrum did not appear to be dictated by a trophic cascade in Las Madres lake, their dynamics being mostly controlled by physical forcing, along with some effect of non-edible primary producers and cladocerans in the first and second periods of mixing, respectively. 4. Our results and others covering early circulation with longer sampling periods suggest that planktonic size spectral dynamics during lake circulation is context-dependent (i.e. varying from one lake to another), thus preventing generalisation. However, when further studies with finer temporal resolution have been carried out, it is likely that clear-cut patterns in the planktonic size spectrum will emerge, arising from the interplay of autogenic plankton dynamics, implying some resistance to community change because of external physical forcing, and the velocity of autumnal mixing
Description14 pages, and figures, and tables statistics.
Publisher version (URL)http://dx.doi.org/10.1111/j.1365-2427.2005.01483.x
Appears in Collections:(IRN) Artículos
(MNCN) Artículos
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