Interaction between non-native predatory fishes and native galaxiids (Pisces: Galaxiidae) shapes food web structure in Tasmanian lakes
Vidal, N and Trochine, C and Amsinck, SL and Barmuta, LA and Christoffersen, KS and Ventura, M and Buchaca, T and Landkildehus, F and Hardie, SA and Meerhoff, M and Jeppesen, E, Interaction between non-native predatory fishes and native galaxiids (Pisces: Galaxiidae) shapes food web structure in Tasmanian lakes, Inland Waters, 10, (2) pp. 212-226. ISSN 2044-2041 (2020) [Refereed Article]
Copyright 2020 International Society of Limnology (SIL)
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 Laymanís food web metrics based on both stable isotope (δ15N and δ13C) values and fish stomach contents in 14 shallow Tasmanian lakes along a NNPF abundance gradient. The food web metrics calculated were (1) range of δ13C (CR) and δ15N (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 galaxiidsí 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.