The role of cladocerans reflecting the trophic status of two large and shallow Estonian lakes

Abstract

The role of pelagic cladoceran communities is discussed on the basis of a comparative study conducted in two Estonian lakes, the moderately eutrophic Lake Peipsi (N tot 700, P tot 40 lg l -1 as average of ice-free period of [1997][1998][1999][2000][2001][2002][2003] and in a strongly eutrophic Lake Võ rtsjä rv (N tot 1600, P tot 54 lg l -1 ). The cladoceran community was found to reflect the differences in the trophic state of these lakes. In L. Peipsi, characteristic species of oligo-mesotrophic and eutrophic waters co-dominated (making up 20% or more of total zooplankton abundance or biomass), whereas in L. Võ rtsjä rv only species of eutrophic waters occurred. In L. Peipsi, the dominant cladocerans were Bosmina berolinensis and Daphnia galeata, while Chydorus sphaericus was the most abundant cladoceran in L. Võ rtsjä rv. The cladocerans of L. Peipsi (mean individual wet weight 25 lg) were significantly (threefold) larger than those of L. Võ rtsjä rv (8 lg). The mean wet biomass of cladocerans was higher and total cladoceran abundance was lower in L. Peipsi compared to L. Võ rtsjä rv (biomass varied from 0.133 to 1.570 g m -3 ; mean value 0.800 g m -3 in L. Peipsi and from 0.201 to 0.706 g m -3 , mean 0.400 g m -3 in L. Võ rtsjä rv; the corresponding data for abundances were: 8,000-43,000 ind m -3 , mean 30,000 ind m -3 for L. Peipsi, 50,000-100,000, mean 52,000 ind m -3 for L. Võ rtsjä rv). Based upon differences in body size, cladocerans were more effective transporters of energy in L. Peipsi than in L. Võ rtsjä rv. Cladocerans proved to be informative indicators of the trophic status and of the efficiency of the food web in studied lakes.

Zooplankton as indicators in lakes: a scientific-based plea for including zooplankton in the ecological quality assessment of lakes according to the European Water Framework Directive (WFD)

“…Long-term investigations of the moderately eutrophic and large Lake Peipsi and the very eutrophic Lake Võrtsjärv have shown that both abundance and biomass of zooplankton increase with eutrophication (Haberman, 1996(Haberman, , 1998. Moreover, the number, biomass and proportion by number and biomass of rotifers increased with tropic state, the proportion of Daphnia of total crustacean biomass decreased, while, in contrast to Danish lakes, copepod biomass decreased (Haberman et al, 2007). In the Estonian lakes, the proportion of rotifers by number and biomass and the biomass of zooplankton are most closely linked with trophic state, while others-as in the Danish lakes-are better indicators of top-down regulating factors.…”

Diet patterns and ontogenetic diet shift of pikeperch, Sander lucioperca (L.) fry in lakes Peipsi and Võrtsjärv (Estonia)

“…Discrepancies between the trophic status and food resources of these lakes (Kangur et al, 2003) were probably the main cause of such variations. According to Haberman et al (2007), in the course of eutrophication the food supplies of juvenile fish decrease. In strongly eutrophic Lake Võrtsjärv, food conditions are not good for pikeperch fry due to low density of large zooplankters like Eudiaptomus gracilis (Sars), Bosmina berolinensis Imhof, Daphnia spp., and L. kindti .…”

Does metazooplankton regulate the ciliate community in a shallow eutrophic lake?

“…A decrease occurred in total ciliate abundances in response to the removal of crustaceans, the opposite of what has been most commonly reported previously in similar experiments (Adrian & Schneider-Olt, 1999;Ventelä et al, 2002). The crustacean community of Võ rtsjärv is mostly composed of small cyclopoids (mainly Mesocyclops leuckarti and Thermocyclops oithonides Sars) and small-bodied cladocerans such as Chydorus sphaericus, Daphnia cucullata and Bosmina longirostris; their numbers and biomasses are relatively low, being obviously affected by strong fish predation pressure (Haberman, 1998;Haberman, Laugaste & Nõ ges, 2007) and by unfavourable feeding conditions due to high abundances of filamentous algae and frequent sediment resuspension (Chow-Fraser & Sprules, 1986;Levine, Zehrer & Burns, 2005). The crustacean community of Võ rtsjärv is mostly composed of small cyclopoids (mainly Mesocyclops leuckarti and Thermocyclops oithonides Sars) and small-bodied cladocerans such as Chydorus sphaericus, Daphnia cucullata and Bosmina longirostris; their numbers and biomasses are relatively low, being obviously affected by strong fish predation pressure (Haberman, 1998;Haberman, Laugaste & Nõ ges, 2007) and by unfavourable feeding conditions due to high abundances of filamentous algae and frequent sediment resuspension (Chow-Fraser & Sprules, 1986;Levine, Zehrer & Burns, 2005).…”