Critical Step 1.3.2: Food web biomanipulation techniques to enhance ecological processes
Lead: Marc Schallenberg
Dave Kelly, Piet Verburg, Kevin Collier, Ian Duggan, Brendan Hicks
The potential for success for classical biomanipulation to improve lake water quality has improved with the arrival of invasive Daphnia species which vigorously graze phytoplankton. Recent summer proliferations of Daphnia pulex in Lake Hayes were correlated with periods of unprecedented water clarity and low phytoplankton biomass. This critical step tests the strength of foodweb interactions in Lakes Hayes and Johnson and postulates that top-down a perch-Daphnia-algae trophic cascade has begun to assist the recovery of Lake Hayes from eutrophication. Once the trophic cascade is confirmed and is better understood, recommendations on how to stimulate the desirable trophic cascade by manipulating fish populations and densities in the lake will be made.
The perch-Daphnia interactions will be studied empirically in the lake using tracers of energy flow including stable carbon and nitrogen isotopes as well as essential fatty acids. The transfer of these tracers through the pelagic food web will be analysed using Bayesian mixing models. In addition, a palaeolimnological study will show how the introduction of perch to the lakes in the early 1900s, the shifts of the lakes to a eutrophic state in the 1960s, and the invasion of the lakes by Daphnia pulex in the 2000s affected Daphnia densities in the lakes. Complex Daphnia-algae interactions in the lakes will be elucidated in enclosure experiments in which densities of Daphnia and key algal taxa will be varied and grazing rates will be measured. These experimental results will be verified in situ using the tracers of energy flow mentioned above. Finally, the information from these different studies will be combined to produce an evidence-based biomanipulation strategy for Lake Hayes and other similar lakes.
Links to other critical steps:
We will evaluate the ability of perch to control Daphnia densities by developing a food-web model, using methods used in CS1.2.3 (Quantifying biodiversity and foodweb responses to lake resilience). This work links to CS1.1.4 (Understanding how multiple stressors affect ecological resilience and integrity) because biomanipulation is designed to weaken lake resilience to recovery from eutrophication and to restore ecological integrity. Thus, information from these critical steps will be shared.
Otago Fish & Game
Otago Regional Council
Friends of Lake Hayes
Lakes Hayes and Johnson (Otago)
- Schallenberg M, Schallenberg L. 2017. Lake Hayes restoration and monitoring plan. Report prepared for the Friends of Lake Hayes. May 2017. 55p.