Production and decomposition rates were calculated for Spartina patens in a mesohaline coastal marsh in Louisiana. Production was estimated to be 800 g m2 yr-1 during 1991 and 1,696 g m-1 yr-1 during 1992. The relative decomposition rate of S. patens stems was -0.001152 g g-1 d-1 which may be restated as a half life of 395 days. Both production and decomposition rates for this area arelow relative