Contribution of adult aquatic insects to riparian prey availability along tropical forest streams

Abstract

The contribution of adult aquatic insects to riparian prey availability at four sites along three hillstreams in Hong Kong was estimated during 2004-2006 dry and wet seasons using light traps deployed at different distances from the banks. The number and biomass of aquatic and terrestrial insects collected were markedly higher during the wet season. Numerically, aquatic insects (especially Chironomidae and Philopotamidae) remained a major catch component along banks throughout the year comprising 77% (range: 61-85%) of total insects. Their contribution to total biomass was higher in the wet season (mean: 50%, range: 33-62%) than during the dry season (mean: 21%, range: 8-45%). Aquatic insect abundance decreased with increasing distance from streams during both seasons: numbers at 10-20 m distance were less than 45% of those at the banks, declining to less than 13% at 80 m distance. No such decline with distance was observed for terrestrial insects, but the limited dispersal of aquatic insects meant total insect catches were highest along stream banks. Changes in biomass with distance from streams were similar to those for abundance. Adult aquatic insects may represent an important water-to-land energy subsidy for riparian predators in Hong Kong, but the magnitude varied seasonally and fell sharply with increasing distance from streams. © CSIRO 2007.