MACROINVERTEBRATES OF A CALIFORNIA SEASONAL WETLAND AND RESPONSES TO EXPERIMENTAL HABITAT MANIPULATION

Responses of macroinvertebrate populations to temporal change and to management of plant cover and water depth were examined in 12 experimental ponds designed to mimic seasonally flooded (early autumn to early spring) wetlands in Suisun Marsh, California. Ponds were flooded in September 1988. Initially, rat-tailed maggots (Eristalis tenax), brine fly larvae (Ephydra millbrae), and mosquito larvae (Culex tarsalis) were numerically dominant components of the fauna in the ponds, but these populations did not persist beyond December. Water boatmen (Trichocorixa verticalis), midge larvae (Cricotopus sylvestris and Chironomus stigmaterus), and hydrophilid beetle larvae (Berosus ingeminatus) were numerically dominant components of the fauna in both autumn and winter, but water boatmen and midge densities declined by March. Amphipods (Eogammarus confervicolus) and three-spined stickleback (Gasterosteus aculeatus) were introduced during initial floodings in September, and they subsequently increased to become numerically dominant components of the pond fauna by February and March 1989. Higher numbers of adult water boatmen and hydrophilid beetles colonized habitats that had 50% of the plant cover removed by mowing than habitats that had not been mowed (100% plant cover). Since mowing also reduced numbers of mosquito larvae, this approach may benefit waterfowl management and reduce public health concerns.