Longitudinal and temporal changes in functional organization of macroinvertebrate communities in the Lam Tsuen River, Hong Kong

Abstract

The functional organization of macroinvertebrate communities along the Lam Tsuen River, New Territories, Hong Kong, was investigated in 1976 and 1978–79. Longitudinal changes in functional group representation in 1976 generally matched those predicted by the River Continuum hypothesis, although shredders were poorly represented in the headwaters. This could be attributed to a lack of shading and limited allochthonous inputs from the scrubland watershed.

In 1978–79 community organization was modified by nutrients and organic matter inputs from domestic and agricultural sources. An increase in generalists and the establishment of deposit-feeder populations in the middle and lower course was accompanied by relative declines in collector, filter-feeder and predator diversity. Shredders and scrapers were also adversely affected. Seasonal influences were mediated through the effects of rainfall on river discharge. The river was ‘flushed-out’ during the wet season and community organization tended toward that seen in 1976. Effects of cultural eutrophication were pronounced during the dry season and marked alterations in middle and lower course functional group representation were noted. Apparently, differing environmental tolerances of individual taxa cause marked changes in functional group representation and community structure in rivers affected by cultural eutrophication.