Rolaniral .]ournal aJlhe Linnean Socieo zyxwvutsrqp (1985), 91: 83-94 zyxwvu The role of fungi in the nutrition of stream invertebrates FELIX BARLOCHER Department zyxwvutsrqp of Biology, Mount Allison University, Sackville, New Brunswick EOA zyxwvu 3C0, Canada Kereiued Seplember 1984, accepled for publication January 1985 BARLOCHER, F., 1985. The role of zyxwv fungi in the nutrition of stream invertebrates. Dead leaves falling into streams are an important food source for many invertebrates. They are generally made more palatable and more nutritious if they are first colonized by aquatic hyphomycetes and other micro-organisms. At least two mechanisms appear to be responsible for this conditioning ellect: mirrobial production (addition of easily digested microbial compounds to the nutritionally poor leaf substrate), and microbial catalysis (conversion of indigestible leaf substances into digestible subunits by microbial enzymes). Different invertebrate species vary in their ability to take advantage of microbial conditioning. This appears to he influenced by their mobility, the range of their food resources and their ability to overcome defense mechanisms of leaf-colonizing micro- organisms. ADDITIONAL KEY WORDS:-Acquired enzymes zyxwvu - aquatic hyphomycetes - conditioning mechanisms ~ detritus food webs - microbial catalysis - microbial production - stream invertebrates, CONl'ENTS Introduction . . . . . . . . . . . . . . . . . . . 83 Palatability and nutritional value ofconditioned leaves . . . . . . . . . 84 Mirrobial cells as food . . . . . . . . . . . . . . . . . 85 Other ronditioning mechanisms . . . . . . . . . . . . . . 87 Microbial production versus microbial catalysis . . . . . . . . . . . 88 Acquired enzymes. . . . . . . . . . . . . . . . . . 89 'I'wo caw studies: Gamrnarus Fabr. and Tipula L.. . . . . . . . . . . 89 Studies with other invertebrates . . . . . . . . . . . . . . 90 Conclusions . . . . . . . . . . . . . . . . . . . 9 I Acknowledgements . . . . . . . . . . . . . . . . . 92 Rrfrrenres. . . . . . . . . . . . . . . . . . . . 92 INTRODUCTION Hynes (1963) pointed out that the banks of undisturbed streams are often densely covered with trees and shrubs. This can be expected to have two important effects, especially in small-order streams: incoming light and therefore primary production will be reduced; and the proportion of detritus derived from riparian vegetation will increase. As a result, the biota in many headwater 83 0024-4074/85/050083 + I2 $03.00/0 zyxwvut 0 1985 The Linnean Soriety of London