DECOMPOSITION RATES OF PURPLE LOOSESTRIFE (LYTHRUM-SALICARIA) AND LYNGBYEI SEDGE (CAREX-LYNGBYEI) IN THE FRASER-RIVER ESTUARY

Using litter bag experiments in the Fraser River estuary in British Co lumbia, we tested for differences in the relative decomposition rates between leaves of purple loosestrife (Lythrum salicaria), an introduce d exotic and a native sedge (Carex lyngbyei). The difference in the me an decay rate coefficient for the two species was significantly differ ent (p < 0.01) and the coefficient for purple loosestrife (0.0110 d(-1 )) was nearly four times higher than for Lyngbyei's sedge (0.0028 d(-1 )). This is the first estimate of the decay rate coefficient for purpl e loosestrife from an estuary. The rapid decay rate of loosestrife lea ves suggests that they supply detritus to the ecosystem in autumn wher eas the much slower decay rate of sedge implies that it supplies detri tus throughout the winter and early spring. Consumer organisms importa nt in juvenile salmon food webs appear to be adapted to take advantage of the detritus provided in these seasons. The findings have implicat ions far habitat management because purple loosestrife has recently in vaded estuaries of the northeast Pacific and may be outcompeting nativ e sedges important in detrital-based food webs.