Drivers of stream fish assemblages and trophic interactions.

Type of content
Theses / Dissertations
Publisher's DOI/URI
Thesis discipline
Ecology
Degree name
Doctor of Philosophy
Publisher
University of Canterbury
Journal Title
Journal ISSN
Volume Title
Language
English
Date
2018
Authors
Fraley, Kevin Marshall
Abstract

Human and environmentally-driven changes in flood disturbance, habitat size, and land cover can affect fish assemblages in streams. However, it is important to understand the mechanisms underlying these so that resource managers can minimize the effects of detrimental perturbations. This is particularly vital for streams that contain endemic, at-risk taxa or species of recreational and economic importance. Therefore, developing functional measures of fish assemblages which summarize energy flow and trophic pathways (e.g., food-chain length) could be useful to quantify the effects of habitat changes on aquatic communities.

To address this, I surveyed thirty headwater Canterbury, New Zealand streams to evaluate fish mass–abundance relationships (size spectra) and stable isotope metrics (food-chain length and carbon range) as functional measures of aquatic ecosystems and their response to the aforementioned habitat factors. I found that these metrics were responsive to increasing habitat size (food chains lengthened), flood disturbance (carbon range and mass–abundance slopes decreased), and riparian land cover types, proving effectual as integrative measures of aquatic ecosystems.

Next, using these newly-vetted metrics, I assessed the effects of small-scale surface water abstractions on fish assemblages and community trophic structure. I found decreased habitat size downstream of water abstractions was associated with lower abundances of large-bodied fishes, shorter food chains, and predatory release for sensitive, small-bodied native taxa.

I then quantified the effects of habitat size and flood disturbance on theorized relationships between fish body mass and trophic position. Here, I found negative influences of these habitat factors on the trophic position of individual fish species, confirming that environmental factors can be as important as fish body size in determining trophic height.

Finally, I identified the specific mechanisms regulating invertebrate and fish trophic height, as well as community biomass through structural equation modelling. I found that flood disturbance negatively affected both the trophic height and biomass of large-bodied non-native salmonids. Additionally, habitat size and land cover types variably influenced the trophic height of small-bodied native fishes and invertebrates, along with algal, allochthonous, invertebrate, and fish biomass.

Overall, my research has advanced understanding of how flood disturbance, habitat size, and riparian land cover affect freshwater fishes and community food webs through modulation of both trophic structure and fish body size. When used in-tandem, fish mass–abundance relationships and stable isotope-derived food-web metrics will be useful measures for monitoring, mitigating, and rehabilitating aquatic communities in the face of pressures caused by land-use change, flow alteration, and non-native species. Thus, these metrics could provide additional tools to inform appropriate management decisions.

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Citation
Keywords
Ngā upoko tukutuku/Māori subject headings
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All Rights Reserved