New Zealand Journal of Marine and Freshwater Research abstracts
Food webs in forest and pasture streams in the Waikato region, New Zealand: a
study based on analyses of stable isotopes
of carbon and nitrogen, and fish gut contents
BRENDAN J. HICKS
Department of Biological Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand
Abstract Stable isotopes of carbon (C) and nitrogen (N) were
studied in 11 stream communities in the Waikato region of New Zealand. From
comparisons of mean d13C and d15N values, food webs in
the shaded, forest streams were clearly based on allochthonous material
(conditioned leaf litter and terrestrial invertebrates). Autotrophs in forest
streams were not a significant C source for the food webs. However, the C
source of food webs in the unshaded pasture streams appeared to be a mixture of
allochthonous and autochthonous material. Conditioned leaf litter appeared to
contribute to the pasture stream food webs, and the d13C and
d15N of some samples of epilithic diatoms indicated their
consumption by invertebrates in pasture streams. Fish ate a wide range of
aquatic invertebrates; longfinned eels (Anguilla dieffenbachii) and
banded kokopu (Galaxias fasciatus) also had a large proportion of
terrestrial invertebrates in their diet. Filamentous green algae were found
only at pasture sites, where they were sometimes abundant. The wide range of
d13C values of filamentous green algae (-18.8 to
-29.7[[perthousand]]) complicated understanding of their role in the stream
food webs. The d13C values of Cladophora were related to
water velocity, with more 13C-enriched values in pools than in runs
(-23.2[[perthousand]] in pools, mean velocity 0.12 m s-1;
-28.1[[perthousand]] in runs, mean velocity 0.24 m s-1). Crayfish
and the gastropod mollusc Potamopyrgus appeared to be the only
invertebrates to eat filamentous green algae.
Keywords stable isotopes; carbon; nitrogen; invertebrates;
fish; food webs; land use
New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31:
651-664
0028-8330/97/3105-0651 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (1100K); (scanned from paper original: notes about this process)
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