Effects of temperature, sestonic algae features, and seston mineral content on cladocerans of a tropical lake

Abstract

-The effects of temperature on the life table, and of seston quality on the individual growth and reproduction of cladocerans from a tropical lake were tested in the laboratory. Life-table experiments were carried out at 17 xC, 23 xC, and 27 xC. Growth bioassays tested the influence of natural seston fractions, separated by net filtration, on cladocerans. The treatments were: (1) total seston plus Scenedesmus spinosus (1 mg C.L x1 ), (2) seston j 36 mm, and (3) seston > 36 mm. Phytoplankton composition, density, and biomass were evaluated during growth experiments, together with sestonic carbon, nitrogen, and phosphorus concentrations. The intrinsic rates of natural increase were higher for Moina micrura and Daphnia ambigua at 27 xC compared to 17 xC. The age at first reproduction of both species was delayed at 17 xC. Growth rates and fecundity of M. micrura were higher in the seston fraction j 36 mm than in the fraction > 36 mm. Higher growth rates and fecundity of Moina minuta were observed in the seston enriched with the green alga in comparison to the seston j 36 mm and > 36 mm. Bosmina longirostris was unable to reproduce at 17 xC and to grow in the seston > 36 mm in one experiment. High densities and/or biomass of large colonial and filamentous algae present in the larger seston fraction could have contributed to reduce growth and reproduction. Episodes of food-quantity limitation may occur, but there was no evidence of mineral limitation, although seston C : P and C : N ratios were always above the limiting values assumed for temperate water bodies. The C : P and C : N ratios are highly influenced by carbon that originates primarily from resuspended detritus from the lake.

Diel horizontal distribution of microcrustaceans and predators throughout a year in a shallow neotropical lake

“…The estimated average algal carbon in the three stations (0.4 -0.6 mgC.L -1 ) are not limiting for some cladocerans in the lake, whose threshold food concentration and the incipient level are, respectively, < 0.025 mgC.L -1 and between 0.1 and 0.2 mgC.L -1 (Bunioto and Arcifa, 2007). Detailed analyses of food quality onshore and offshore are in progress, because laboratory experiments with cladocerans from the Lake Monte Alegre showed lower intrinsic rates of population growth (r) and fecundity of Moina micrura and Ceriodaphnia cornuta in the microplankton fraction (> 20 µm) (Fileto et al, 2004). This fraction, however, promoted a higher fecundity of the macrophyte-associated cladoceran Simocephalus mixtus.…”

“…This fraction, however, promoted a higher fecundity of the macrophyte-associated cladoceran Simocephalus mixtus. Bosmina longirostris, from a shallow Brazilian lake connected to the Paranapanema River, was unable to reproduce in biossays with the largest phytoplankton fraction (>36 µm) (Fileto et al, 2010). However, among microcrustaceans, Bosmina and Ceriodaphnia, which can feed on nonalgal resources, are better able to explore the littoral where heterotrophic conditions can prevail (Smiley and Tessier, 1998).…”

“…Adults of Tilapia (166-245 mm standard length) are mainly limnetic, occupying the 1-4 m layer in the water column (Arcifa and Meschiatti, 1993). They are diurnal, not abundant, spawn in nests built onshore in the warm-wet season, and influence the phytoplankton mostly through nutrient excretion in comparison to grazing (Silva, 2004). Even in higher abundance in mesocosms (1 ind./2.5 m 3 ) than in the lake, Tilapia did not lower zooplankton densities (Silva, 2004).…”

“…They are diurnal, not abundant, spawn in nests built onshore in the warm-wet season, and influence the phytoplankton mostly through nutrient excretion in comparison to grazing (Silva, 2004). Even in higher abundance in mesocosms (1 ind./2.5 m 3 ) than in the lake, Tilapia did not lower zooplankton densities (Silva, 2004). Main littoral predators are odonates, found in low abundance within macrophyte stands, fish (Meschiatti and Arcifa, 2002), and notonectids, distributed mostly onshore near the edge of macrophytes.…”

Horizontal distribution of Cladocera in a subtropical lake marginal to a river

“…Macroelements, such as nitrogen and phosphorus, together with suspended matter, are potential nutritional factors for the lake and promote a high abundance of cladocerans. Although no significant variation was found for chlorophyll-a, an index of phytoplankton biomass, on this side of the lake, suspended matter from organic detritus might be an alternative food resource to algae (Fileto et al, 2010). Conversely, D. brevireme, D. spinulosum, D. birgei, B. longirostris, Ceriodaphnia cornuta f. intermedia, M. micrura and M.…”