Interaction between non-native predatory fishes and native galaxiids (Pisces: Galaxiidae) shapes food web structure in Tasmanian lakes

Vidal, Nicolas
Trochine, Carolina
Amsinck, Susanne L.
Barmuta, Leon A.
Christoffersen, Kirsten S.
Ventura, Marc
Buchaca, Teresa
Landkildehus, Frank
Hardie, Scott A.
Meerhoff, Mariana
Jeppesen, Erik
Non-native fish invasions threaten native fauna and ecosystem functioning, not least in isolated island lakes. In Tasmania, where the native fish are mostly galaxiids, 9 non-native freshwater fish species have been introduced over the past 150 years, with uncertain ecological outcomes. We evaluated the effects of non-native predatory fishes (NNPF) and various environmental and biological variables on the trophic niche of native fish (galaxiids) and potential cascading effects. We analysed Layman's food web metrics based on both stable isotope (delta N-15 and delta C-13) values and fish stomach contents in 14 shallow Tasmanian lakes along a NNPF abundance gradient. The food web metrics calculated were (1) range of delta C-13 (CR) and delta N-15 (NR) centroid distance (CD) and (2) standard ellipse area. Our results showed that NNPF relative abundance in the fish catch per unit effort was negatively related to the galaxiids' trophic niche metrics (e.g., CRG, NRG, and CDG), trophic position, and the pelagic contribution to the diet. Moreover, the proportion of galaxiids in the diet of NNPF was higher in turbid lakes. The zooplankton standard ellipse area was negatively correlated with the pelagic contribution to the NNPF diet, and NNPF relative abundance was positively correlated with the maximum body size of calanoid copepods. While our results suggest a negative effect of NNPF on the trophic niche of galaxiids, the cascading effect on phytoplankton biomass was weak. Non-native predatory fish affect native fish prey, and the outcome of these interactions should be considered for conservation purposes, particularly for island lakes, such as those in Tasmania.


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Freshwater ecosystems and their biodiversity are presently seriously threatened by global development and population growth, leading to increases in nutrient inputs and intensification of eutrophication-induced problems in receiving fresh waters, particularly in lakes. Climate change constitutes another threat exacerbating the symptoms of eutrophication and species migration and loss. Unequivocal evidence of climate change impacts is still highly fragmented despite the intensive research, in part due to the...
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Citation Formats
N. Vidal et al., “Interaction between non-native predatory fishes and native galaxiids (Pisces: Galaxiidae) shapes food web structure in Tasmanian lakes,” INLAND WATERS, pp. 212–226, 2020, Accessed: 00, 2020. [Online]. Available: