LEAF-LITTER PROCESSING AND ENERGY-FLOW THROUGH MACROINVERTEBRATES IN A WOODLAND POND (SWITZERLAND)

Energy generated by leaf litter processing and its flow through the as sociated macroinvertebrate community was quantified in a pond near Gen eva (Switzerland). Annual density, biomass, and production on oak (Que rcus robur) leaf litter were assessed for all macroinvertebrate taxa w ith emphasis on predators. Empirical energetic relations provided an e nergy budget for the macroinvertebrate community. On 1 m(2) of pond bo ttom, the processing of 5641 kJ of oak leaf litter resulted in 8.5% of leachate (6 days), and after 1 year 32% of material remained; the oth er 59.5% was biologically (animal or microbial) converted, including 1 1.2% processed by shredders. The mean annual density of associated mac roinvertebrates was 51374 individuals, mean biomass was 3.53 g (dry ma ss) and production was about 1451 kJ (or 65 g). Predator production wa s 170 kJ/m(2), non-chironomid primary consumer production was 101 kJ/m (2) (including 57 kJ from shredders) and chironomid primary consumer p roduction was estimated at 1180 kJ/m(2) Predators contributed to a hig h proportion of total biomass (39%) but to a smaller amount of product ion (12%) or density (6%). In this two-stepped food-chain mainly based on detritus, the transfer coefficient between first level (detritus+p rimary producers) and third level (secondary consumers) was high (2-2. 5%) and indicated efficient conversion of energy. This high efficiency was partly related to the reutilization of fine particulate organic m atter by the collectors. The production estimate measured on leaf litt er was compared with two other predominant substrates (Typha latifolia stems and Char a sp.), and exhibited the highest value. This study sh ows how leaf litter can constitute a direct source for high secondary production and be an efficient energy source in freshwater ecosystems. It is also demonstrated that a woodland pond can support a high macro invertebrate production as compared with other freshwater ecosystems.