Zooplankton Composition and a Water Quality Assessment of Seventeen Waikato Lakes Using Rotifer Community Composition

TR 2008/26
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Report: TR 2008/26
Author: Ian C Duggan (University of Waikato)

Abstract

Zooplankton species composition was documented from 17 Waikato lakes from net haul samples collected in late 2007 (summer) and early 2008 (autumn). The lakes examined were Harihari, Mangahia, Maratoto, Ngahewa, Ohinewai, Okowhao, Parangi, Rotokawau, Rotomanuka, Serpentine East, Serpentine North, Serpentine South, Taharoa, Tutaeinanga, Waahi, Waikare and Whangape.

A variety of species was observed during the study, including 41 rotifer, 5 cladoceran and 3 copepod taxa, mites and mysid shrimps. Most taxa recorded were typical inhabitants of New Zealand lakes. However, there appears to be a growing nonindigenous component to the zooplankton, with the freshwater jellyfish Craspedacusta sowerbyi (2 lakes), the rotifer Conochilus exiguus (1 lake) and two Daphnia species (D. dentifera and an apparently new invader; widespread) recorded during this study.

Rotifer-inferred TLI estimates ranked the lakes from best to poorest in the following order: Lake Serpentine East (3.38), Maratoto (3.43), Serpentine South (3.76), Harihari (4.74), Ngahewa (4.93), Parangi (5.00), Mangahia (5.03), Serperntine North (5.10), Rotomanuka (5.32), Taharoa (5.68), Okowhao (6.11), Tutaeinanga (6.15), Ohinewai (6.67), Waikare (6.79), Rotokawau (7.46), Whangape (7.66) and Waahi (7.88). This ranking is comparable to assessments made using different methods elsewhere. In a previous Waikato lake study, the rotifer-inferred TLI value from Lake Taharoa samples collected in late 2006 was 2.7 (i.e., oligotrophic). A higher value in the current study may indicate that the rotifer community had a delayed response to a recent decline in water quality in this lake. Alternatively, it strengthens the supposition that accurate assessments using this method should be made when several (i.e., quarterly) samples are taken throughout the year. Nevertheless, the maximum difference in inferred TLI values between summer and autumn samples from a single lake in the current study was 2.0.

Zooplankton Composition and a Water Quality Assessment of Seventeen Waikato Lakes Using Rotifer Community Composition [PDF, 61 KB]