New Zealand Journal of Marine and Freshwater Research abstracts

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Short communication 

Comparison of coded abundance and fixed count rapid assessment techniques for biomonitoring in New Zealand streams

Ian C. Duggan
Mike R. Scarsbrook*
John M. Quinn

National Institute of Water and Atmospheric
 Research Limited
P.O. Box 11 115
Hamilton, New Zealand
*Author for correspondence.

Abstract   We compared the performance of fixed count subsampling (100, 200, and 300 individuals) and coded abundance (rare, common, abundant, very abundant, very very abundant) with full count sampling for rapid assessment biomonitoring. Examining change in the Quantitative Macroinvertebrate Community Index (QMCI) and % Ephemeroptera, Plecoptera, and Trichoptera (EPT) values between sites upstream and downstream of pollution inputs, we found c. 1:1 relationships between assessments made using both rapid assessment methods and full counts. However, variability was greater using coded abundance, and to a degree that is likely to lead to incorrect assessments on occasion. The loss of information content in the data set, defined as Bray-Curtis distances based on community composition between the two rapid assessment methods and those of full counts, was significantly greater using coded abundance than fixed counts. Assessment of stream invertebrate community composition using fixed counts, even as low as 100 animals, provided superior results to coded abundance in the two independent data sets tested.

Keywords   biomonitoring; methods; coded abundance; fixed counts; invertebrates

M01088 Received 6 December 2001; accepted 17 September 2002; Published 20 March 2003
New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37: 23-29
0028-8330/03/3701-0023 $7.00 © The Royal Society of New Zealand 2003

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