EVALUATING SEAGRASS LEAF-LITTER DECOMPOSITION - AN EXPERIMENTAL COMPARISON BETWEEN LITTER-BAG AND OXYGEN-UPTAKE METHODS

Comparison of the decay rates of leaves of the seagrass Posidonia ocea nica (L.) Delile have been performed under different experimental cond itions (season, depth, and kind of material), using two methods: litte r-bag incubation and oxygen uptake measurements. Weight loss in litter -bags was higher (i) in summer than in winter (ii) in shallow zones th an In deep zones (iii) in senescent leaves still attached to the plant than in leaf litter fragments. Oxygen uptake rates were higher in sum mer add in senescent leaves, but no effect of the incubation depth was shown, indicating that mechanical effects are relevant for weight los s inside bags but not for metabolic processes. When compared on the sa me basis (carbon loss), decay rates obtained from oxygen uptake measur ements were always lower than those obtained using litter bags. On ave rage, only 40% of the weight loss observed in the litter bags is expla ined by respiratory consumption.