New Zealand Journal of Marine and Freshwater Research abstracts
Temporal and spatial quantification of aquatic invertebrate drift in
the Maruia River, South Island, New Zealand
Karen A. Shearer
John W. Hayes
John D. Stark
Cawthron Institute
Private Bag 2
Nelson, New Zealand
email: karens@cawthron.org.nz
Abstract We investigated temporal (day-to-day and
season) and spatial (reach) variability of drift with the aim of guiding
sampling protocol for quantifying drift at the whole river or reach scale.
Overall, we found aquatic drift density and biomass varied considerably seasonally
(CV = 72.9, 88.1) and to a lesser extent spatially (CV = 31.3, 30.7) and
from day-to-day (CV = 45.2, 39.4). Although spatial and day-to-day variation
in drift density and biomass were similar, sampling logistics suggest spatial
sampling would be more cost-effective and less time consuming. Drift density
and biomass estimated from top samplers was often higher than estimates from
samplers near the streambed or mid-water column. A reliable estimate of mean
densities and biomass at a site may require only two samplers-a top sampler
and either a middle or bottom sampler. In our study, we calculated that sampling
at four sites over 1 or 4 days at one site would be required to obtain a
95% CI within 50% of the mean drift density. Eight sites over 1 or 10 days
at one site would be required to achieve a 95% CI within 25% of the mean
drift density.
Keywords temporal variation; spatial variation; invertebrates;
sampling; aquatic invertebrate drift
M00080 Received 13 November 2000; accepted 27 February 2002; published 17 September 2002
New Zealand Journal of Marine and Freshwater Research, 2002, Vol. 36:
529-536
0028-8330/02/3603-0529 $7.00 © The Royal Society of New Zealand
2002
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