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LAKE ECOSYSTEM RESEARCH NEW ZEALAND


Lake Ecosystem Restoration New Zealand is a collection of research programmes aimed at monitoring and restoring lake ecosystems. It encompasses a diverse group of researchers and projects including remote sensing, real-time monitoring of lakes and inflows, which often forms the basis for lake and catchment modelling. Research is also conducted into the detection, control and eradication of vertebrate and invertebrate invasive species and the identification of source contaminants in catchments.

News and examples of the latest research being conducted can be found below and under the Research themes.

Latest Research


Eye On Lakes

Eye on Lakes is an MBIE Smart Ideas research programme aimed at developing improved ways of monitoring harmful cyanobacterial blooms using satellite images. Almost daily satellite overpasses provide images of the whole of New Zealand,  providing detailed knowledge about our environment. These images can provide visual and quantitative assessment of water quality and the state of the environment on a spatial scale not possible with traditional monitoring.

Nationwide, only about 40 lakes are currently monitored for cyanobacteria. This monitoring is time consuming and costly. It requires field work and specialist lab analysis. There are almost 4000 lakes in New Zealand, so we can not feasibly monitor changes in water quality or provide warnings of toxic algal bloom formation with on the ground sampling. The method used by Eye on Lakes is based on detecting nuances of colour in lake water. Cyanobacteria have a special colour signature, invisible to the naked eye, but detectable using specialised instrumentation.

There are over 240 lakes in the Waikato region larger than 1 ha, many of which have persistent cyanobacteria blooms (e.g., Lake Waikare). These lakes are extremely valuable for a range of reasons: cultural and food provision, habitat for native species, ecosystem services such as flood mitigation and nutrient removal, but have come under pressure from human activity such as farming and forestry. But changes in water quality may go unnoticed because not all lakes can be monitored using traditional grout-based methods. Satellite Earth observation can supplement and expand current monitoring programmes for lake water quality. Moreover, it provides a historical data sources going back 30 years allowing researchers to investigate events and trends in environmental signals. Eye on Lakes is set to conclude at the end of 2021.

Research lead: Mortiz Lehmann

Time lapse of all cloud-free images from January 2020 to October 15 2020. This shows some of the intense algal blooms and sediment discharge events in Lake Waikare in the Waikato region

These images were taken from a drone used for water sampling. The sampling container is visible at the end of the red line. It contrasts the colour of the lake during a blooms of different types of algae.  Credit: David Schmale.


Fish-host Partitioning By Kākahi Species

PhD student Michele Melchior is using field and laboratory techniques to study kākahi – host fish interactions to improve conservation efforts.

New Zealand has two freshwater mussel species (kākahi) that occur in northern Waikato streams. The widely distributed Echyridella menziesii and the threatened Echyridella aucklandica. Until recently, little information existed on the basic biology of these species which can live for more than 50 years. Both species undergo an obligate symbiotic phase on fish during their early life stage as larvae (termed glochidia).

Previous research suggests that E. menziesii glochidia are host fish generalists, able to attach on a range of native fish taxa. By comparison, host-relationships for E. aucklandica have remained unknown. However, recent evidence from Michele’s PhD of contrasting glochidia release and infection behaviour of the two species (e.g broadcast release in E. menziesii and conglutinate release in E. aucklandica i.e. mucus packages containing glochidia that mimic fish food) has highlighted the potential for host – resource partitioning and that E. aucklandica may be a host fish specialist (able to attach only to few closely related species) rather than E. menziesii which is a host generalist.

To assess glochidia – host relationships, field analyses were undertaken via electrofishing and gee-minnow trapping in Waikato streams known to contain large populations of both Echyridella species. Results from the field were validated in the laboratory via host-fish infection trials, to further understand metamorphosis success and infection intensity on fish in E. aucklandica compared to E. menziesii.

From field studies E. aucklandica was found to only attach to common smelt (Retropinna retropinna), while E. menziesii attached to a range of fish taxa, but not to common smelt. This confirms that host-fish partitioning is occurring between kākahi species and this is the first observation of host specific attachment by E. aucklandica glochidia.  Subsequent laboratory investigations confirmed common smelt as a host for E. aucklandica, with high prevalence of infection (80%) on fish samples, but low mean infection intensities in all infected individuals ( =1.6 glochidia per infected fish). Suggesting that common smelt are not the preferred primary host species, but further research is being conducted. Furthermore, E. aucklandica and E. menziesii exhibited contrasting reproductive modes once attached on compatible host fish species, requiring contrasting attachment sites and developmental modes (metamorphosis durations and growth on the host).

Because kākahi are entirely dependent on hosts to complete their life-cycle, a lack of suitable hosts (particularly for specialists with a small host range) may lead to a lack of juvenile recruitment, and increasing vulnerability to co-declines, and potential extinctions should the host-glochidia relationship be disrupted. Knowledge of fish hosts is essential in developing conservation management strategies such as restoration of appropriate habitats for threatened unionid populations and facilitating upstream passage for migratory host fish at critical times of the year (i.e glochidia release).

This research is part of NIWA's Cultural Keystone Species research programme, which is funded by the Ministry of Business, Innovation and Employment.

Research lead: Kevin Collier

Developing E. aucklandica encapsulated on gill filaments of common smelt (top) and ventral view of head region (bottom) in common smelt with encapsulated E. aucklandica (white circle) on the left side (under operculum) on ventral gill segment (glochidia length is 432 µm).

One month old Echyridella aucklandica transformed on common smelt gill

Life-cycle of E. aucklandica which releases glochidia enwrapped in conglutinates that infest on fish which then metamorphose and drop off as benthic juvenile mussels.


Land Use Driven Changes In Fish Production

Hemispherical camera analysis to determine canopy cover over a Taranaki stream

New research conducted by PhD student Morgan Riding aims to examine the effects of land use changes from forest to pasture and, how associated factors such as light availability and temperature regimes affect fish biomass in Tarankai streams.Land use change from forest to pasture results in an increase in light availability, directly affecting temperature regimes, resulting in changes to physicochemical properties and stream metabolism. As fish get larger, the requirement for food increases, therefore fish biomass naturally reflects the available food within a stream system. If resources are limited, these fish are likely to perish or move to a more favourable environment. Consequently, the density, diversity and biomass of fish may be altered as a result of land use change

Stream physical variables such as temperature, light, width, velocity, elevation and conductivity were measured in association with biological variables such as periphyton, macroinvertebrate and fish biomass at 12 sites around Mt Taranaki. Fish abundance was greater in pasture sites than in forested sites and total fish biomass in pasture sites (mean 26.7 g m-2) was four times greater than in forest sites (mean 6.2 g m-2).Temperature showed the strongest positive correlations with variables. Total fish biomass was most closely related to mean summer water temperature (r = 0.81), percentage dissolved oxygen (r = 0.75) and mean bank light intensity (r = 0.69), suggesting that primary production rather than allochthonous inputs drove ecosystem function.

Investigating drivers of stream production is essential for understanding how aquatic species respond to anthropogenic pressures under varying levels of modification.

Research lead: Brendan Hicks