Drift of aquatic macroinvertebrate larvae in Manganuiateao River, central North Island, New Zealand

Abstract

Drifting aquatic invertebrate larvae in Manganuiateao River, central North Island, were collected at bi-monthly intervals between January and October 1989 from 2 sites (3 stations per site) over 4 diel periods in 24 h (dawn to mid-morning, mid-morning to mid-afternoon, mid-afternoon to dusk and dusk to dawn).Samples were also collected from 1 station over 1-2 h periods for 24 h in December 1989.A total of 68 aquatic invertebrate taxa were taken in the drift.Chironomidae, Beraeoptera roria and Helicopsyche spp.were the dominant taxa overall ( > 10% of invertebrates on all dates and sites combined) between mid-afternoon and dusk, the only period that complete sets of samples were collected on most dates.Hydrobiosidae, Deleatidium spp., Coloburiscus humeralis, Plecoptera and Pycnocentrodes spp.comprised > 10% of larvae on at least one date.Drift density between mid-afternoon and dusk was highest in March and May (92-151 individuals 100 m" 3 h _1 ) and lowest in July (18-28 100 m^h" 1 ).Diurnal peaks in drift were evident around dusk and dawn when samples were collected at 1-2 h periods for 24 h, but this pattern was not detected in 2 other months that complete sets of drift samples were collected over 4 continuous periods in 24 h.Densities of Deleatidium spp., Plecoptera and Chironomidae larvae in the drift were significantly correlated with the density of invertebrates collected in two sets of comparable benthic samples, suggesting that drift of these taxa could be partly density dependent.Drift density of Chironomidae larvae was inversely correlated with mean flow in the week preceding sampling, but significant positive correlations were detected with preceding flow regime for Deleatidium spp., Plecoptera and Pycnocentrodes spp.We discuss some factors that are likely to influence invertebrate drift in Manganuiateao River, including the potential role of blue duck predation.