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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.

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 dieffenbachiai) 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.
Type
Journal Article
Type of thesis
Series
Citation
Hicks, B. (1997). Food webs in forest and pasture streams in the Waikato region,New Zealand: A study based on analyses of stable isotopesof carbon and nitrogen, and fish gut contents. New Zealand Journal of Marine and Freshwater Research, 31(5), 651-664.
Date
1997-12-01
Publisher
RSNZ Publishing
Degree
Supervisors
Rights
The final, definitive version of this article has been published in the New Zealand Journal of Marine and Freshwater Research, 31(5), 1997. (c) The Royal Society of New Zealand 1997 at the The Royal Society of New Zealand webpage.