CS17 Invasive Species
Date: Thursday, June 13, 2002
Time: 11:15:00 AM
Location: Sidney
 
KhanTA, University of Ballarat, Ballarat, Victoria, Australia, t.khan@ballarat.edu.au
Khan, M, T, University of Ballarat, Ballarat, Victoria, Australia, m.khan@ballarat.edu.au
Wilson, M, E, University of Ballarat, Ballarat, Victoria, Australia, m.wilson@ballarat.edu.au
 
DIETARY OVERLAP, PREDATION AND TROPHIC CASCADE: EXOTIC FISH INVASION IN LAKES OF WESTERN VICTORIA, AUSTRALIA
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Lakes of western Victoria are shallow (2-3m), slightly saline (3-8ppt) and eutrophic (total Phosphorus 0.1-5mg/L and total Nitrogen 3-8mg/L). In these lakes exotic biomass exceeded native biomass by a factor of two. Dietary similarity and overlap between exotic carp and native fish species was high. The only notable piscivore in these lakes was exotic redfin. Lakes bloomed in summer and coincided with high numbers of small carp. Since nutrients appear non-limiting, we explored the role of carp in enhancing algal blooms through 'top-down' effects. Gut analysis of carp larvae (N=900) revealed that <2cm larvae fed exclusively on microcrustacea and this was reflected in their decline. To confirm carp mediated trophic cascade, when ponds stocked with lake zooplankton, algae were consumed efficiently and algal numbers and biomass were significantly lower than control ponds. Ponds stocked with low zooplankton numbers were intermediate. Complete elimination of cladocera and subsequent increase in algal biomass occurred after 12 days in ponds stocked with carp. Zooplankton and algal populations were unaffected when nutrients but no fish were added and also in control ponds.