Effects of Eutrophication on Flagellates Associated with Eichhornia crassipes: An Experimental Approach

Abstract

The effects of nutrient enrichment on density, biomass and on the relative contribution of pigmented and heterotrophic flagellates to the total abundance of all flagellates associated with Eichhornia crassipes were evaluated through mesocosm experiments over 33 days. Two triplicate treatments (nitrogen and phosphorus addition and a control treatment) were colonized, producing six mesocosm systems. The only variable that showed significance was flagellate density. Density increased significantly with increased nutrient concentrations in both flagellate groups, suggesting the importance of bottom-up control mechanisms. However, the time lag and the low magnitude response to density, as well as the lack of significant variation in biomass with respect to fertilization, suggested that a complex relationship is responsible for influencing the structure of flagellate communities associated with vegetation during nutrient enrichment in these food webs. IntroductionThe deterioration of water bodies caused by eutrophication from anthropogenic activities represents a severe environmental problem (TUNDISI, 2003). This excess of nutrients is considered to be one of the major pollution sources in aquatic ecosystems (ESTEVES, 1998). The result is a series of biological events including: an increase in the dominance of certain trophic levels, such as an increase in algal biomass; modification of microbial loop components (bacteria, flagellates and ciliates) and significant impacts to higher trophic levels (SAMUELSSON et al., 2002;AUER et al., 2004).In this sense, aquatic communities have been used as descriptors of environmental changes (HIGUTI et al., 2005); especially microorganismal assemblages because of their ability to act as bioindicators of aquatic pollution (FOISSNER, 1992).Due to their small body size, high metabolic rates and short life cycles (DUPUY et al., 2007), the organisms that constitute the microbial food chain respond rapidly to changes in environmental conditions (AUER et al., 2001). In addition, they play an essential role in fast nutrient cycling, the mineralization of organic compounds and the production and transfer of organic matter in aquatic environments (AZAM et al., 1983 Among these microorganisms, the flagellate protozoans are important components, having a significant role in aquatic system metabolism. The pigmented flagellates (PF) may have important roles in primary production (SAFI and HALL, 1997), whereas heterotrophic flagellates (HF) are considered to be the main consumers of bacteria (SIMEK et al., 1999). When they are consumed by metazoans (SHERR et al., 1988), the role of flagellates is compound many times; they become the dominant trophic link as the productivity of the pico -and nanoplankton is transferred to higher trophic levels (HWANG and HEALTH, 1997).Studies of the planktonic zone have shown that the abundance of flagellates is frequently associated with environmental trophic conditions and, consequently, is influenced by the bottom-up control mechanisms that are related t...

The Effect of Peatland Restoration on Ciliate Communities: Long-Term Analyses

“…In the B− habitat, as the content of biogenic substances decreased, so did the abundance of ciliates. Bauer et al, Pereira et al and Buosi et al also showed a strong relationship between abundance and the availability of nutrients [43,51,52]. Such correlations were also observed by Mieczan and Tarkowska-Kukuryk and by Mieczan et al [26,50].…”