Factors affecting the bacteria-heterotrophic nanoflagellate relationship in oligo-mesotrophic lakes |
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Authors: | Tadonleke Remy D; Pinel-Alloul B; Bourbonnais N; Pick F R |
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Institution: | Geotop Université du Québec à Montréal, CP 8888, SUCC. Centre Ville, Montréal, QC, H3C 3P8, 1 Gril Département de Sciences Biologiques, Université de Montréal, CP 6128, SUCC. Centre Ville, Montréal, QC, H3C 3J7, 2 Ministère de LEnvironnement et de la Faune, Gouvernement du Québec, Sept-Îles, H3C 3P8 and 3 Faculty of Sciences, University of Ottawa, Ottawa, PO Box 450, STN, Ontario, K1N 6N5, Canada |
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Abstract: | The coupling between bacteria and heterotrophic nanoflagellates(HNF) was examined in nine lakes of low productivity for evidenceof the effects of various metazooplankton (i.e. rotifers, cladoceransand copepods) on this relationship. We considered the size ofcladocerans and, in contrast to most previous across-systemstudies, the three strata of the water column (i.e. epilimnion,metalimnion and hypolimnion). Rotifers were numerically dominantin all lakes and accounted for 4584% of total metazooplanktonabundance, while the abundance of large cladocerans was relativelylow, ranging from 0.066 to 15.2 ind. L1. The across-lakerelationship between bacteria and HNF was significant in thedeeper strata (meta- and hypolimnion) but not in the epilimnionand in the two groups of lakes separated on the basis of theiraverage number of large cladocerans (<5 and >5 ind. L1,respectively). The results confirmed the negative impacts oflarge cladocerans on HNF, but also showed that rotifers, probablythrough grazing on HNF, may be an important factor causing variationin the bacteriaHNF relationship in unproductive waters.Quadratic models best described the relationships between metazooplanktonand the ratio of bacteria to HNF. This ratio seemed to be aresult of complex interactions between several factors, includingthe zooplankton composition and abundance and the depth of thelake. Indeed, this ratio significantly decreased across lakes,with increase in depth. In addition, shallower lakes (having<5 large cladocerans L1 and fewer Polyarthra vulgaris)tended to have more bacteria and HNF and a higher ratio of bacteriato HNF than deeper lakes (which had >5 large cladoceransL1 and substantial proportions of P. vulgaris). We suggestthat the epilimnion, metalimnion and hypolimnion of lakes betaken into account when analysing the bacteriaHNF relationshipas well as the cascading effects of zooplankton on microbialcommunities. |
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