Role of animal detritivores in the breakdown of emergent plant detritus in temporary ponds

Abstract

Few in situ studies have investigated the biological drivers of detritus processing in shallow lentic systems, despite abundant evidence that vascular plant detritus is a primary source of nutrients and energy. In particular, the relative importance of microbial decomposers and animal detritivores to overall detritus breakdown is poorly documented. Caddisfly larvae (Trichoptera: Limnephilidae) are often the biomass-dominant animal detritivores in high-elevation and high-latitude ponds and wetlands in the northern hemisphere. The larvae of many limnephilid caddisfly species are shredders that rely on detritus as their primary food source, and they may therefore play an important role in litter breakdown in lentic systems. Here, we manipulated abundances (present/absent) of caddisfly larvae in shallow montane ponds in Colorado, and compared sedge detritus breakdown rates across treatments. We found that coarse particulate organic matter (CPOM) was converted to fine particulate organic matter (FPOM) 2 to 3× faster when caddisflies were allowed access to the detritus than when not, indicating that caddisflies play a key role in litter breakdown in these temporary habitats. Dietary data from the 6 species of caddisflies in the ponds revealed that all primarily consume CPOM derived from vascular plants, although the ratios of CPOM and FPOM in the diets varied among species. The biomass of caddisflies relative to detrital inputs is particularly high at our study sites compared with other eutrophic, low-elevation wetlands. Thus, we suspect that animal detritivory relative to microbial processing may be especially high in these ponds. Future in situ, whole-community studies in basins that differ in hydroperiod, nutrient status, and ratio of detrital inputs to detritivore biomass will be needed to construct a general model of detritus breakdown in shallow lentic freshwater habitats.