Artificial substrate macroinvertebrates in the Waikato River: 25 years on

Report: TR 2011/25

Author: KJ Collier, MP Hamer, MW Davenport

Abstract

Macroinvertebrates were monitored over 2006-07 using artificial multiplate samplers at six sites on the Waikato River (Huka Falls, Ohakuri, Narrows, Horotiu, Ngaruawahia and Rangiriri), repeating a survey conducted in 1980-82.

The data provide:

• direct comparisons between surveys conducted 25 years apart
• assessment of macroinvertebrate abundance and community composition on perspex samplers for six bi-monthly occasions, and
• comparisons between hardboard or perspex samplers.

In 2006-07, the macroinvertebrate community colonising substrates at these sites was dominated by mollusca (primarily the snail Potamopyrgus antipodarum) in the upper river (Huka and Ohakuri sites) and by crustacea (primarily the amphipod Paracalliope fluviatilis) in the lower river. The use of wood versus perspex substrates did not significantly influence the composition or diversity of macroinvertebrate communities but did affect the abundance of some taxa, indicating that comparisons of composition and diversity can be made between substrate types.

Diversity of the macroinvertebrate community in 2006-07 tended to increase with distance downstream, reaching a peak at the Ngaruawahia site before declining at the Rangiriri site. These longitudinal changes likely reflect downstream patterns in water quality, shore-zone habitat diversity and flow variability within the river.

Downstream patterns of diversity detected in 2006-07 corresponded to those reported by Davenport (1982), and were similar for taxonomic richness although more taxa were collected overall in 2006-07. There appeared to have been a change in macroinvertebrate community composition (excluding oligochaete worms) from the 1980-82 study, with a shift in dominance from chironomid larvae to snails in the upper river in 2006-07, and a shift from dominance of snails to crustaceans in the lower river.

Artificial substrate macroinvertebrates in the Waikato River: 25 years on
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