Acute Effects of Microcystis aeruginosa from the Patos Lagoon Estuary, Southern Brazil, on the Microcrustacean Kalliapseudes schubartii (Crustacea: Tanaidacea) W. Montagnolli, A. Zamboni, R. Luvizotto-Santos, J. S. Yunes Unidade de Pesquisas em Cianobacte ´rias (UPC), Departamento de Quimica, Fundac ¸a ˜o Universidade Federal do Rio Grande (FURG), Cx Postal 474, CEP 96201-900, Rio Grande/RS, Brazil Received: 12 January 2003 /Accepted: 6 September 2003 Abstract. Toxic blooms of the cyanobacterium Microcystis aeruginosa, a microcystin producer, have been observed in the past two decades in the Patos Lagoon estuary (southern Brazil). This cyanobacterium reaches the estuary from northern waters and accumulates as toxic blooms in the shallow margins of the environment. Microcystins are phosphatase (PP1 and PP2A) inhibitors and cause animal death via alteration of the liver cell cytoskeletons and intrahepatic hemorrhage. The massive accu- mulation of toxic material affects the survival of several ben- thonic estuarine local organisms. The tanaidacea Kalliapseudes schubartii is a benthonic estuarine species which occurs at high densities throughout the year in mixohaline areas of the Patos Lagoon. This microcrustacean is of high ecological relevance and plays an important role in the estuarine food web, as it is consumed on a large scale by estuarine fish. This work verifies the acute toxicity of aqueous extracts of M. aeruginosa RST9501 and of sediments spiked with lyophilized material of the same strain on K. schubartii; it also evaluates the sublethal effects on tanaidacean oxygen consumption rates and glycogen levels under acute exposure to M. aeruginosa aqueous extracts. The strain M. aeruginosa RST9501 was cultured in BGN/2 medium. The aqueous extracts were prepared using the lyo- philized material from the strain cultures. Acute tests were performed over 96 h at a salinity of 15, at six toxic concentra- tions, and resulted in an average 96-h LC50 of 1.44 mg ml -1 . The spiked sediment tests were performed with a 10-day du- ration, using the lyophilized material in three proportions of powder/sediment and showed an average LC50 of 1.79 mg ml -1 . Oxygen consumption was determined after 24 and 48 h of incubation in adult organisms exposed to sublethal aqueous extract concentrations and showed a significant increase at the highest concentrations. This suggests alterations in the organ- ism’s metabolism by exposure to the cyanobacterium extract. The glycogen levels were determined with a commercial kit (Glicox 500; DOLES Ltd.); after 24 and 48 h the dosages were administered in the same organisms utilized in the oxygen consumption test and did not demonstrate significant differ- ences. The results demonstrate the possible risks of intoxica- tion to which the natural populations of K. schubartii were exposed in the environment and emphasize the importance of studies involving sublethal concentrations of M. aeruginosa to other organisms of the trophic web in this aquatic system. Cyanobacterial blooms have several consequences for water quality and their collapse frequently causes high mortality among aquatic animal populations (Vasconcelos et al. 2001). Among many species of cyanobacteria that can develop toxic blooms, Microcystis aeruginosa is one of the most common and is a matter of great concern (Chorus and Bartram 1999). The cyanobacterium Microcystis aeruginosa produces toxins called microcystins, monocyclic heptapeptide molecules, of which over 65 structural variants are known. Most of the variants are potent hepatotoxins and tumor promoters in mam- mals (Codd et al. 1999; Sivonen and Jones 1999). At the molecular level, microcystins are serine/threonine phosphatase PP1 and PP2A inhibitors, resulting in hyperphosphorylation of proteins, affecting intracellular signaling, cell growth, and dif- ferentiation processes, and inducing cell disturbance (Toivola and Eriksson 1999). Previous works have shown that microcystin can be conju- gated with the tripeptide glutathione (GSH), through a conju- gation reaction catalyzed by glutathione-S-transferase (GST) (Pflugmacher et al. 1998; Takenaka 2001; Vinagre et al. 2003). The microcystin–GSH complex has a less inhibitory effect on phosphatases, clearly showing that this conjugation reaction is involved in detoxification processes (Metcalf et al. 2000). The enzyme (GST) is reported to be involved in detoxification reactions of several kinds of pollutants, such as metals, fungi- cides, and pesticides (Freedman et al. 1989; Gallagher et al. 1992; Maracine and Segner 1998). Different aquatic organism species from all trophic levels in the web are susceptible to microcystins, these include bacteria, protozoa, macrophytes, green algae and diatoms, and micro- and mesozooplankton, as well as invertebrates and fish (Christ- offersen 1996). A number of reports have demonstrated the sensitivity of different species of marine and freshwater crus- tacea to Microcystis aeruginosa cells and microcystins (Delaney and Wilkins 1995; Salomon et al. 1996; DeMott Correspondence to: J. S. Yunes; email: dqmsarks@furg.br Arch. Environ. Contam. Toxicol. 46, 463– 469 (2004) DOI: 10.1007/s00244-003-2304-6 ARCHIVES OF Environmental Contamination and T oxicology © 2004 Springer-Verlag New York LLC