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RESEARCH PRODUCT

Plankton Ecology and Diversity

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description

In this chapter we describe plankton responses induced by fluctuating hydrology and eutrophication process in the semi-arid TDNP wetland. We have followed the planktonic community since 1992, at seasonal and interannual scales, covering as well the spatial heterogeneity of the wetland. The studied planktonic components were bacterioplankton, autotrophic picoplankton, nano and microphytoplankton and zooplankton, including ciliates. Plankton has been studied in terms of species composition (diversity), functional groups, spatial heterogeneity, population dynamics. The present data from this wetland allow us to determine which factors (resources and conditions) are relevant for each group and how their specific responses affect the food web. Bacterioplankton biovolume ranged between 0.1 and 5.0 mm3 l−1, autotrophic picoplankton (0–1.7 mm3 l−1), nano- and microphytoplankton (0.03–774 mm3 l−1, more than 90% nanoplankton), zooplankton (0.01–280 mm3 l−1, more than 50% ciliates). Plankton community shows an evident spatial heterogeneity, with the seasonal and inter annual dynamic of all groups differing between wetland areas. Shallowness and hydrologic conditions impinge strongly on the seasonal dynamics of plankton communities; patterns during drought and wet periods were different. Therefore, a lack of pattern among plankton assemblages is the most remarkable feature. We suggest that alternative states of plankton taxonomic structure in this eutrophic semiarid wetland occur as a sequence of substitutions, due to close coupling with sediment and hydrological disturbance. The autogenic trajectory is not attained and the trophic relationships or top-down control are possibly irrelevant.