© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1434-2944/04/5 – 612– 0453 ANA SAMPAIO 1 *, RUI CORTES 2 and CECÍLIA LE ˜ AO 3 1 CETAV – Departamento de Engenharia Biológica e Ambiental, University of Trás-os-Montes e Alto Douro, Apartado 1013, 5001–911 Vila Real, Portugal; e-mail: asampaio@utad.pt 2 Departamento Florestal, University of Trás-os-Montes e Alto Douro, Apartado 1013, 5001–911 Vila Real Codex, Portugal 3 Life and Health Sciences Research Institute, School of Health Sciences, University of Minho, Campus de Gualtar, 4710–057 Braga, Portugal Yeast and Macroinvertebrate Communities Associated with Leaf Litter Decomposition in a Second Order Stream key words: yeast, ergosterol, invertebrates, leaf litter Abstract The composition of yeast and macroinvertebrate communities was studied on black alder, blue gum eucalyptus and English oak leaves decaying in a stream during a six-month period. ANOVA analysis showed significantly different values (p < 0.0001) of yeast and macroinvertebrate densities among the three leaf litters. Some yeast species such as Cryptococcus albidus (SAITO), C. laurentii (KUFFERATH), Rhodothorula glutinis (FRESENIUS), R. colostri (CASTELLI), and Debaryomyces hansenii (LODDER and KREGER-VAN RIJ) were present in all litter types. Other yeasts were restricted to a specific type of lit- ter. Macroinvertebrates were dominated by collectors-gatherers on oak and eucalyptus leaves. Shredders reached highest densities in alder leaves. 1. Introduction Leaf litter breakdown is a key process in low order streams (MINSHALL, 1967; ABELHO and GRAÇA, 1998). The decomposition rate of leaves entering the stream depends on abiot- ic factors such as temperature, flow, physical abrasion (PETERSEN and CUMMINS, 1974), pH (CHAMIER, 1987), nitrate and phosphate concentrations (POZO, 1993), and biotic factors such as initial litter quality (MELILLO et al., 1984), invertebrate and microbial colonisation (ANDERSON and SEDELL, 1979). Leaf decay has traditionally been described as a sequential process, which proceeds from leaching to physical abrasion, microbial conditioning and invertebrate colonization. However, some authors (e.g., GESSNER et al., 1999) have suggest- ed that these stages occur simultaneously and are interactive. They also propose that this interaction can involve competition for nutrients between fungi and shredder communities. During breakdown, a succession of organisms occurs, reflecting an adjustment of biolog- ical communities to the surrounding environment (FRANKLAND, 1998). Succession studies during litter decay in aquatic systems have been confined to single biological groups such as macroinvertebrates (e.g., BASAGUREN and POZO, 1994; ROBINSON et al., 1998; COLLIER and HALLIDAY, 2000), and aquatic hyphomycetes (e.g., CHAUVET et al., 1997). These asex- ual and filamentous fungi are often found on decomposing leaves, wood and twigs in well- aerated water bodies. Hyphomycetes have been identified in the early stages of litter decom- position, and proved to have a direct impact on decay, by synthesising cellulolytic, pecti- nolytic and proteolytic enzymes. Other studies have demonstrated their importance in Internat. Rev. Hydrobiol. 89 2004 5–6 453– 466 DOI: 10.1002/iroh.200410764 * Corresponding author