Small-scale habitat additions engage local communities and support ecosystem restoration in New Zealand streams
12 December, 2024
By Isabelle Barrett
Waterways Centre, Lincoln University, New Zealand
isabelle.barrett@lincoln.ac.nz
Issie Barrett is a lecturer in the Waterways Centre: a joint research centre between Lincoln University and the University of Canterbury, New Zealand. She is a freshwater ecologist interested in instream habitat restoration, and an international FBA member.
Edited by Rachel Stubbington, Nottingham Trent University
Rachel is both a Fellow of the Freshwater Biological Association and long-standing Editor of FBA articles. If you would like to submit an article for consideration for publication, please contact Rachel at: rachel.stubbington@ntu.ac.uk
Introduction
River restoration projects often focus on riparian management actions such as planting and fencing, under the assumption that improved water quality will result in direct benefits for ecosystem health. Such projects can help rivers to recover from degradation, but successful recovery of instream communities likely requires additional steps targeting physical habitat quality.
Ecologically focused instream habitat restoration typically aims to increase habitat complexity, creating more niches to support higher biodiversity. Methods such as channel reconfiguration and addition of large woody material or boulders can be effective; however, their implementation typically requires heavy machinery, consenting and deep pockets. This type of restoration is thus often beyond the physical and financial means of non-governmental organisations and community groups.
So, how can we enhance instream habitat without breaking the bank? I present four case studies from New Zealand which trialled instream habitat additions as a practicable restoration tool and an opportunity for community engagement.
Case study: Habitat units, Upper Rakaia
I had been taught to be wary of physical habitat restoration as a restoration tool, citing the flaws of the Field of Dreams hypothesis (Palmer et al. 1997): even if we build it, they often do not seem to come. However, challenging my scepticism, as I collected in cotton strip assays (a measurement of organic matter breakdown) during a field trip, I noticed that they were covered in Megaleptoperla stoneflies – organisms not recorded in Surber samples from nearby existing habitat (Fig. 1). These stoneflies were thus clearly drifting through the system, but only choosing to stay once additional habitat was provided.
Figure 1. Megaleptoperla stoneflies found on cotton strips deployed in Glenariffe Stream.
So, in the terms of the Field of Dreams, are the invertebrates not coming – or are they coming, but not staying? In other words, does a lack of recovery reflect the failure of habitat restoration to provide suitable habitat – or limited colonist availability? In addition, is the failure to distinguish between these drivers a limitation of typical monitoring designs? Identification of factors limiting post-restoration community recovery often resorts to speculation, despite the availability of tools to detangle them. In this study, I developed a sampling methodology to tease apart limiting factors and therefore optimise future restoration planning.
This experiment tested instream habitat additions – carefully crafted habitat units – as a proof-of-concept for use of such additions both as a restoration tool and an opportunity to detangle factors influencing community recovery. To achieve the latter goal, we devised a comprehensive sampling programme including analysis of pre-existing and colonist communities, using Surber and drift sampling, respectively.
Figure 2. Habitat units made from dowel rods, cotton, bundles of sticks and tī kouka (cabbage tree leaves) deployed in Glenariffe Stream.
Habitat units were designed to be simple to construct using biodegradable, readily available materials, and optimised to create heterogeneous habitat for stream invertebrates (Fig. 2). These invertebrates primarily disperse via downstream drift, and potential colonists continue to drift until they find suitable habitat. Therefore, by comparing drifting invertebrates to those in existing habitats and those which established in habitat units, we identified the mechanisms underpinning community recovery, including insufficient habitat quality, lack of available niche space and biotic interactions (e.g. competition). Habitat units were installed in Glenariffe Stream (Upper Rakaia), which forms a system of channels across a high-country wetland. The surrounding land has recently been retired from agriculture and is undergoing restoration. Water quality is good, but instream habitat is homogeneous.
Figure 3. Means and 95% confidence intervals for invertebrate densities and taxa richness in pre-existing stream habitat (from Surber samples), colonist assemblages (from drift samples) and habitat units; drift densities are not comparable and so are not shown.
Six weeks post-installation, invertebrate communities occupying habitat units were significantly more abundant, more diverse and included more sensitive taxa than communities from existing habitat, indicating a positive impact of habitat additions (Fig. 3). Furthermore, the taxonomic composition of drifting invertebrate communities was more similar to communities within habitat units than in existing habitat, suggesting that habitat additions facilitated establishment of additional taxa arriving via drift. Based on this evidence, I adapted this approach for use in further trials, and multiple projects have been borne from the original habitat unit designs.
Case study: Macroinvertebrate motels, Auckland
The Habitat Unit 2.0 – colloquially termed ‘macroinvertebrate motels’ – were developed in collaboration with Auckland Council to test the capacity of small-scale habitat additions to boost depauperate invertebrate communities at degraded sites in forested, rural and urban streams following cyclone Gabrielle (Barrett et al. 2024). The project was also an opportunity to test this concept in naturally soft-bottomed streams, with adaptations including stilts which could be adapted (sawn off) depending on sediment depth (Fig. 4).
Figure 4. The Habitat Unit 2.0, in construction and installed at three sites.
The responses of richness and densities were very similar to case study 1 (Fig. 5). However, at the rural site we observed colonisation of the habitat units by homogeneous communities of degradation-tolerant taxa, suggesting that habitat additions may enable a degraded community to proliferate rather than facilitating establishment of newly colonising taxa.
Figure 5. Invertebrate densities and richness in pre-existing stream habitat (Surber), colonist assemblages (drift) and habitat units. Squares: forested; triangles: urban; circles rural sites. See Fig. 3 for further details.
Case study: Kete piringa, Taumutu
While the original habitat units used dowel rods and cotton, initial concepts also included use of plant materials to create habitat structure. When the original trials began, I contacted a local iwi (Māori tribe) near Christchurch. The wahine (women) of Te Taumutu Rūnanga embraced the idea, using harakeke (flax) to weave habitat additions predominantly as habitat for fish and invertebrates. Their designs were inspired by wahakura (baby bassinettes) and were named ‘kete piringa’ (baskets of refuge; Fig. 6).
Figure 6. The author working with the local community to weave kete piringa (baskets of refuge).
The kete were deployed instream beside the marae (communal gathering place), and I captured underwater video footage of fish using the habitat (Fig. 7).
Figure 7. Kete piringa in Waikēkēwai stream inhabited by a common bully Gobiomorphus cotidianus.
Case study: Aquatic bug bags, Waikirikiri | Selwyn River
In this project, I worked with schools along the Waikirikiri (Selwyn River). Students aged 6–10 created ‘aquatic bug bags’ using coffee sacks stuffed with tī kouka (cabbage tree leaves). The bug bags gave students an opportunity both to unleash their creativity and to learn about and connect to their local river. We deployed 62 bug bags and took additional kick samples to compare colonising assemblages with those in the surrounding environment. Unfortunately, many bags were lost during a large flood event; however, most still contained some invertebrates, much to the amazement of the children. Such projects have the power to engage the community and inspire guardianship of our waterways.
Figure 8. The author working with school students to install aquatic bug bags along the Waikirikiri (Selwyn River).
Final thoughts
From an ecological perspective, these case studies suggest that short-term, small-scale habitat additions are a valuable restoration measure that can indicate whether more permanent methods (e.g. installation of large woody material) would be worthwhile. Our initial trials suggest that habitat units are a simple way to boost invertebrate populations, especially at sites affected by disturbances such as floods.
From a societal perspective, habitat additions have immense value in education and outreach. Simple habitat structures can be easily deployed and retrieved from riverbanks, providing hands-on opportunities for local community members including school students to learn about and appreciate freshwater ecosystems. As such, this approach is an accessible means of enabling people to connect with their local fresh waters in new and inspiring ways.
Acknowledgements
Thanks to Shelley MacDonnell, Maddison Jones, Holly Fleming and Amber Taylor for field assistance and support. Thanks to Matt Stanford for championing environmental education far beyond his role of Enviroschools Facilitator for Selwyn, and to Enviroschools students and teachers who participated in the bug bags project. Thanks to Te Taumutu Rūnanga for their support, engagement and hard work. Auckland Council, Environment Canterbury, the Selwyn Waihora Zone Committee, and Lincoln University provided funding.
Data availability statement
Contact Issie to request data underpinning this article.
Copyright statement
All figures are copyrighted by the authors.
References
Barrett, I.C. et al. 2024. A short-term home with long-term potential: temporary aquatic habitat additions to support macroinvertebrate colonisation. New Zealand Journal of Zoology. https://doi.org/10.1080/03014223.2024.2430594
Palmer, M., Ambrose, R.F. & Poff, N.L. 1997. Ecological theory and community restoration ecology. Restoration Ecology 5: 291–300. https://doi.org/10.1046/j.1526-100X.1997.00543.x
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