Zooplankton biomass in tropical reservoirs in southern Brazil

Abstract

In order to test the hypothesis that zooplankton biomass distribution (total and taxonomic groups) was influenced by the nutrient concentration and primary productivity distribution in three tropical reservoirs, subsurface samples were taken in the fluvial, transitional and lacustrine regions of three reservoirs (oligotrophic, mesotrophic and eutrophic) in southern Brazil (Paraná State) in March and September 2002. Zooplankton biomass ranged from 0.04 to 264.47 mg DW m -3 . Higher biomass values were observed for cladocerans (73.60%; 0.01-259.86 mg DW m -3 ), followed by copepods (22.05%; 0.01-69.69 mg DW m -3 ) and rotifers (4.35%; 0.01-11.52 mg DW m -3 ). In general, the total zooplankton, rotifer, cladoceran and copepod biomass, and chlorophyll-a and total nutrient concentrations showed a similar longitudinal distribution within the reservoirs. Total zooplankton, rotifer and cladoceran biomass were related to the chlorophyll-a concentration, and zooplankton biomass was related to the total phosphorus distribution. This may have been due to the significant multicolinearity between the chlorophyll-a and total phosphorus concentrations. Cyanobacteria influenced the taxonomic group biomass results by interfering with the filter feeding in larger zooplankton species, which favoured the dominance of smaller species. As regards the longitudinal distribution of copepod biomass, cyanobacteria biomass determined the displacement of the microcrustaceans to the fluvial region of Iraí Reservoir. Our results supported the hypothesis formulated and the primary productivity was the major predictor of the zooplankton biomass distribution in the reservoirs.

Zooplankton communities as eutrophication bioindicators in tropical reservoirs

“…Under the more eutrophic conditions of sites JA-01 and JA-02 during the dry season and JA-01 during the rainy season, the highest cladoceran biomasses were observed, a response similar to that reported by Bonecker et al (2007) and Serafim-Jú nior et al (2010) that observed an increase in Cladocera biomass and abundance at points with highest trophic state condition. This strong relationship between the Cladocera and the most eutrophic period and variables, like total phosphorus and chlorophyll a, is evidenced by the CCA.…”

“…This close relationship between the values of biomass and TSI was also observed by Bonecker et al (2007) in three reservoirs in Paraná State.…”

“…An increase in zooplankton biomass has been related by many authors to a rising level of eutrophication, since, to a large extent, a higher trophic state will lead to increased resource availability, which, in turn, leads to growth in the biomass of zooplankton populations (Serafim-Jú nior et al 2010, Bonecker et al 2007). …”

Relations among planktonic rotifers, cyclopoid copepods, and water quality in two Brazilian reservoirs

“…Generally, few species are dominant in high densities in eutrophic reservoirs (Sendacz & Kubo, 1982;, feeding mainly on Cyanobacteria blooms and associated bacteria-according to Maitland's (1978) affirmative. In oligotrophic and also in mesotrophic reservoirs studies indicated higher richness and lower abundances (Nogueira, 2001;Bonecker et al, 2007). However, observed higher species richness in an eutrophic reservoir, as well as Velho et al (2005); Perbiche-Neves et al (2007) and Bini et al (2008) in another eutrophic reservoir.…”

“…For example, Nogueira (2001) and Sampaio et al (2002) have found high frequency of Collotheca sp., Conochilus coenobasis, C. unicornis, Keratella americana, K. cochlearis and Polyarthra vulgaris in oligotrophic reservoirs of Paranapanema River, in contrast with Matsumura- , who observed abundance peaks of C. coenobasis and K. americana in an eutrophic reservoir. Another example is the study of Bonecker et al (2007), that studied 30 reservoirs in Paraná State (Brazil), and concluded that Hexartra intermedia, Synchaeta pectinata and Trichocerca insignis indicated eutrophic conditions and Trichocerca pusilla and T. similis mesotrophic conditions. Thus, only the high richness of Brachionidae can be pointed out as indicator of eutrophic conditions, even considering the other relationships commonly found in the literature.…”