New Zealand Journal of Marine and Freshwater Research abstracts
Distribution of the New Zealand crayfish Paranephrops zealandicus in
relation to stream physico-chemistry, predatory fish, and invertebrate
prey
NISIKAWA USIO
COLIN R. TOWNSEND
Department of Zoology
University of Otago
P. O. Box 56
Dunedin, New Zealand
Abstract Summer distributions of the crayfish
Paranephrops
zealandicus White, and of potential predators and prey, were investigated
in 30 pools along a stream in Otago, New Zealand. Environmental variables were
regarded as independent and invertebrates as dependent variables for
young-of-the-year (YOY) and adult crayfish. YOY and adults were negatively
associated with trout presence and suspended solid concentrations, and
positively with wood cover. Adults were further negatively associated with
current velocity and positively with depth, leaf cover, and percentage sand. In
contrast, YOY were positively associated with coarse substrates. The results
are consistent with hypotheses that crayfish are vulnerable to sedimentation
and trout predation. Furthermore, coarse substrate and cover may be important
because they provide shelter from predation and cannibalism. Deep habitat,
however, may act as a refuge from terrestrial predators and/or provide detritus
storage for adult crayfish. Densities of adults were negatively associated with
those of
Megaleptoperla, Tanypodinae, and Scirtidae, but positively with
Chironominae. The negative relationships are probably consequences of
bioturbation and predation by crayfish. However, the positive relationship with
Chironominae indicates that any predation/bioturbation effect may be outweighed
by crayfish shredding leaves and enhancing food supply for these collector
invertebrates. The effects of crayfish may propagate into lower trophic levels
both directly and indirectly.
Keywords koura; trout; Paranephrops zealandicus;
distribution; invertebrates; physico-chemistry
M99068
Received 10 November 1999; accepted 2 February 2000
PDF file of entire paper: medium quality (821K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
