Ingestion and assimilation rates of Oocystis sp. by Daphnia magna

Ingestion and assimilation rates of Oocystis sp. by Daphnia magna

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Ent'ironmental Pollution (Series A) 31 (1983) 77-95 Ingestion and Assimilation Rates of Oocystis sp. by Daphnia magna in Treated Wastewaters Bruno Myrand* & Jo61 de la Nofiet * D6partment de Biologie, t Centre de Recherche en Nutrition, Universit6 Laval, Sainte-Foy, Qu6., Canada G1K 7P4 A BSTRA C T This study was aimed at examining the possibility of using Daphnia magna to recotrer the phytoplankton produced in high concentration during the biological treatment of wastewaters. Ingestion rate, assimi- lation rate and assimilation efficiency were measured for grown under controlled experimental conditions in secondarily treated waste- waters. The rate of ingestion was higher at 15°C than at 20°C and depended on the high concentrations of algae (Oocystis sp.) used." 10 and 50 mg C litre-1. The rate of assimilation was constant at about 1.8 Ilg C per per hour. It is proposed that the incipient limiting let, el of ingestion corresponds to the concentration where the assimilation rate is maximum. At food concentrations higher than this le~,el of ingestion, control mechanisms normally maintain a constant ingestion rate and pret'ent superfluous feeding. Our results revealed the inefficiency of these mechanisms at high food concentrations, leading to superfluous feeding. Net, ertheless, retreals itself as a good candidate for the fi'ltration of Oocystis produced in wastewaters. INTRODUCTION Although the effluent from the sewage treatment plant is an improvement over untreated effluent, this discharge is still rich in nutrients (N and P) which accelerate the eutrophication of the collector stream (Knapp, 77 Era:iron. Pollut. Ser. A. 0143-1471/83/0031-0077,/$03"00 © Applied Science Publishers Ltd, England, 1983. Printed in Great Britain
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78 Bruno Myrand, Jok'l de la Nolle 1971). It was suggested by Goldman & Ryther (1976) that nitrogen removal from wastewater for the sole purpose of protecting the quality of natural waters was a waste of time and money if the fertilising potential of these wastewaters was not used to produce food. In this perspective, the controlled growth of phytoplankton in treated wastewaters is therefore attractive. In fact, integrated food chains have been developed where microalgae are filtered by invertebrates (Gordon et al., 1982). The animal biomass produced solves the problems of the difficult harvesting of the algal biomass (Pavoni 1974) and of the poor digestibility of this biomass in humans and domestic animals (Goldman, 1979). In most systems already studied, treated wastewaters are diluted with sea water, thus favouring the growth of marine diatoms. The search for filtering organisms has thus been focused on economically attractive species living in marine or brackish waters: oysters Crassostrea virginica, mussels Mytilus edulis, scallops Mercenaria mercenaria and brine shrimps Artemia salina. Results have been reported as encouraging (Tenore 1973; McShan 1974; Goldman & Ryther, 1976). Other research workers have studied systems using only fresh water (Moraine 1979; Picard 1979), so it has now become necessary
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This note was uploaded on 04/30/2011 for the course EEMB 142C taught by Professor Alldredge/osborn during the Spring '08 term at UCSB.

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Ingestion and assimilation rates of Oocystis sp. by Daphnia magna

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