Life histories and production of two trichopteran shredders in New Zealand streams with different riparian vegetation

Abstract

Abstract The life histories, microdistributions, and annual production of two trichopteran shredders Oeconesus maori (Oeconesidae) and Pycnocentria forcipata (Conoesucidae) were investigated in three small streams at Hinewai, Banks Peninsula, New Zealand. The riparian forest at the three sites was dominated by different tree species: mahoe, Melicytus ramiflorus; tree fuchsia, Fuchsia excorticata; and red beech, Nothofagus fusca—each of which had a distinctive litterfall pattern. Mean annual biomass of detritus (> 0.5 mm) on the stream beds was high (777–1982 g DW m−2 ) but temporal changes in biomass did not reflect litter fall patterns. O. maori was most abundant in pools. Small larvae appeared in late spring and most were in instars 4 and 5 in late autumn and winter. Mean larval densities in the three streams ranged from 90 to 1126 m−2. Annual production was greatest in the mahoe‐dominated stream. Larvae of P. forcipata were most abundant on small falls and among root mats. Its life history was difficult to interpret. Mean larval densities ranged from 59 to 332 m−2 and annual production was again highest in the mahoe‐dominated stream. We found little evidence for a shredder response in these three streams (i.e., the maximisation of shredder biomass at the time of maximum litter conditioning). A general lack of predictably pulsed litter inputs to streams, and a species‐poor shredder fauna make it unlikely that such a response will be found in many New Zealand running waters.