engleski

How do different metazooplankton groups (Rotifera, Cladocera, Copepoda) respond to community stress caused by flooding? A case study from Danubian floodplain Lake (Kopački rit, Nature Park)

Zooplankton communities play an important role in freshwater ecosystems as the biotic factor controlling the abundance of phytoplankton and linking it to organisms of higher trophic levels. According to the extended flood pulse concept, in floodplains there are three hydrological phases: isolation (I), flow pulse (II) and flood pulse (III). In the present study we evaluated the effects of flooding on metazooplankton community stress index and recovery, with emphasis on different hydrological phases. The area of Kopački rit Nature Park is regularly flooded by the River Danube and is one of the biggest floodplains in Europe. Sakadaš Lake, as the deepest lake in the floodplain, was selected as a sampling site. Samples were collected monthly, from June 2007 until December 2011 at the deepest part of the lake. Two samples at each site were collected: at the surface (20 centimetres below the surface) and the bottom (40 centimetres above the bottom). A total of 137 species of metazooplankton species was recorded with 114 species belonging to Rotifera, 15 species of Cladocera and eight species of Copepoda, all of which can be found inhabiting eutrophic waters. SIMPER analyses of total biomass showed significant differences between different hydrological phases and percentage of difference was between 78.62% and 81.15 % in surface water layers while total difference in bottom water layers ranged between 78.13% and 81.37%. ABC analyses of total zooplankton community abundance/biomass data showed the highest level of community stress during flow pulse, with value of W = -0, 012. ABC analyses of planktonic crustaceans (Cladocera, Copepoda) data differed among different hydrological phases and life stages. Nauplii and copepodites showed stress in all phases (W(I) = -0, 009, W(II) = -0, 031, W(III) = -0, 144) with increase in community stress during flood pulse. Adult individuals showed no stress during isolation phase (W = 0, 085), while visible decline in stability was present during flow and flood pulse (W(II) = 0, 011, W(III) = -0, 044). Biodiversity of rotifers was the highest during small water age (<10 days) and was recorded to decrease with higher water age (>20 days), in which planktonic crustaceans repopulated. Even during the flood phase, but where water age was high, the Lake conditions resemble those of an isolated lake where biotic interactions play an important role in structuring metazooplankton community. Flow pulse, or constanly changing water level (especially short term), coused the highest stress in metazooplankton community, where only several species of Rotifera flourished and there were almost no adult individuals of planktonic crustaceans recorded. These results suggest the importance of hydrological phases in structuring metazooplankton communities in floodplain lakes, as well as the impact of water age on metazooplankton capacity to recover.

metazooplankton, community stress, ABC analyses

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