Freshwater bioremediation using native mussels - focussed on shallow eutrophic lakes
Joint MBIE Endeavour Smart Idea. Successful 2018.
Project Update (July 2019):
In January 2019 the bioremediation project team were welcomed to Matahuru Marae, Ohinewa, by Ngaati Mahuta. The pōwhiri was timed to coincide with the visit of freshwater mussel expert Professor Chris Barnhart from Missouri State University (USA) who, together with Dr Bob Brown, (Manaaki Whenua Landcare Research) spent two weeks at NIWA Hamilton with the rest of the team on a mussel ecophysiology “research blitz”.
We put adult mussels through their paces in respiration chambers, by exposing them to different temperatures and oxygen concentrations designed to simulate some of the more extreme conditions they are likely to experience in Lake Ohinewai. We also examined their filtration rates in response to different diets and discovered that adult mussels markedly decrease their filtration rate in response to a standard commercial diet that until now, we have been using in our rearing system. We discovered that “rinsing” the diets improves the mussel’s filtering response - but nonetheless it indicates that we need to investigate ways to improve their diet, especially for culturing juvenile mussels. The new filtration parameters will be used in the next model update for Lake Ohinewai.
Unfortunately our kāeo kohanga work reached another dead end this breeding season, literally. In an attempt to avoid the one month “die-off” of our cultured juveniles we trialed transferring batches of juvenile mussels outside to five different locations in a hope that a more diverse natural diet would increase their survival rates, but none survived. This failure did however give us some insights that we will use next breeding season, in combination with other gems of insight gleaned from trials conducted in related kāeo research.
Finally, we also conducted an initial survey of Lake Ohinewai and found a small population of adult mussels, which supported our successful application for a DOC permit to work in the lake and translocate mussels from the lake bed to rafts and cages. The next steps in the project are to conduct a more thorough dive survey of the lake in combination with a lakeside kāeo wānanga with Ngaati Mahuta. We are about to commence raft construction and trials and we will conduct the second two week “research blitz” (of three) in January 2020.
- Manaaki Whenua Landcare Research
- University of Waikato & Waikato DNA Sequencing Facility
- Missouri State University
- Matahuru Marae, Ngaati Mahuta at Matahuru Marae
- AM2 & Associates
- Joint MBIE Endeavour Smart Idea - Successful 2018.
To develop native freshwater mussel (kākahi/kāeo) rafts (or suspended cages) to assist lake restoration through biofiltration. The focus of our proposal is to return degraded, turbid, shallow lakes towards their original clear, macrophyte-dominated state.
The project has four workstreams:
Lab-based work examining the mussels sublethal responses to extreme environmental conditions (e.g., low dissolved oxygen and high temperatures) that they are likely to experience on “mussel rafts” in a shallow lake. This workstream will provide design parameters for our raft construction & operation and increase the chances of the mussels thriving on the rafts.
- Field Trials
Research based at Lake Ohinewai where we will trial different raft and net designs and examine their localised effect on water quality.
Improvement of a pre-existing mathematical model of Lake Ohinewai using parameters from workstreams 1 & 2. The model will be used to explore questions such as “how many mussels per raft, and how many rafts will it take to have a significant impact on the water quality of Lake Ohinewai”? and “how can we optimize the impact of the rafts (e.g., by strategic placement in the lake”)?
- Kāeo Kohanga
We are trialling improvements to our culturing system to overcome the bottleneck where 95% of our cultured juvenile mussels “die off” at 1-2 months of age. We are also examining genetic parameters around “eco-sourcing” mussels from local populations in situations where donor populations are needed to restock lakes where mussels have completely died out.
Year 1 of 3-year project
Freshwater mussels (known as kāeo or kākahi) throughout much of Aotearoa are considered a “Cultural Keystone Species”. They were an important mahinga/hauaanga kai resource – and are still collected today. They feed by filtering large quantities of water at an average rate of 1 litre per mussel per hour. There are indications that populations are declining in many streams and lakes (including Lake Ohinewai) – they are however, thriving in other locations (e.g., Lakes Karaapiro and Taupō).
Meanwhile many shallow lakes, especially in the Waikato are severely degraded as a result of factors such as increasing nutrient inputs. The lakes have “flipped” into a state where rooted aquatic plants can no longer survive. The lake sediments are no longer held in place by the aquatic plants and so the lake waters remain permanently muddy (or turbid) – and this is made worse by the presence of pest fish species like koi carp and catfish.
Our team is inspired by the idea that freshwater mussels could be part of the restoration process in shallow lakes. At present, it is thought that mussels are slowly dying out in shallow lakes when oxygen levels decrease at the lake bed. We would like to test the idea of moving mussels from the lake bed, up onto rafts or into baskets, to enable them to survive and continue filtering the water. If the mussels can survive, we would then like to understand what would happen if we increased the numbers on rafts up to thousands. We believe we can learn more by running small scale trials in a shallow lake and in the laboratory.