Planktonic interactions with an austral bias: Implications for biomanipulation: Fid-Bau Portal

Planktonic interactions with an austral bias: Implications for biomanipulation

Burns, Carolyn W.

The conceptual model of trophic structure in a typical north temperate lake that underlies attempts at biological manipulation to improve water quality is reviewed in relation to the trophic structure and community composition of planktonic food webs in New Zealand and Australian lakes. New Zealand's relatively simple food webs are characterized by an absence of obligate piscivores and few vertebrate and invertebrate planktivores; manipulation of fish stock to improve water quality has not been attempted. The largest crustacean zooplankton in Australasia, and potentially the most effective grazers of phytoplankton, are Daphnia carinata and calanoid copepods (Boeckella spp.). Their potential capacities to remove algae and colonial cyanobacteria (Microcystis, filamentous forms) from waterways are discussed in relation to colony size and concentration, toxicity, selectivity, and digestibility. The potential of D. carinata to suppress rates of increase in phytoplankton biomass may be lowered by its sensitivity to crowding and starvation, and its susceptibility to predation by fish. Decisions to use biomanipulation as a management tool to improve water quality should be based on the results of a whole lake study and take into consideration relevant obligations to preserve the biodiversity of native species, and curb the spread and dominance of exotic species. Programmes that are based on reductions in biomass of planktivorous fish should be complemented by control of nutrient loads (integrated management).