Feeding Interactions and Cycling of Peat in a Bog Lake

Abstract

Peat particles enter a bog lake as a result of wave erosion of the shore. By the time the peat has settled from suspension, its calorific and protein content has increased by 23 and 200% respectively, due presumably to colonization by microorganisms. After passing through the gut of larvae of a dominant mud-dwelling midge, Chironomus lugubris, the rate of O2 consumption of the peat (now in the form of fecal pellets) has risen by over 87.degree.. The increase in microbial activity responsible for the change suggests that fecal pellets themselves are potentially valuable as food. These pellets are not eaten by C. lugubris larvae. This is attributed to the relatively large size of the pellets and to their resistance to mechanical and microbial fragmentation. A change in dominant micro-organisms from bacteria on peat particles, to fungi on the pellets, may also be a contributory factor. Another common inhabitant of the lake, the cladoceran Chydorus sphaericus, seems to depend on the midge feces for food, and its feeding activities break the pellets down to a size again usable by C. lugubris. Fragmentation is accompanied by yet another increase in nutritional value, indicated by a rise in bacterial numbers of about 300% over fecal values. The interaction between these 2 dominant animals is beneficial to both species.