The effects of turbidity and complex habitats on the feeding of a galaxiid fish are clear and simple

Abstract

The habitat used by animals plays an important role in their interactions with predators and prey. By using complex habitats such as areas of dense macrophyte cover in response to elevated predation risk, small fishes may reduce their foraging success. Because the threat of predation by introduced brown trout increases the use of complex habitats by the threatened Galaxias auratus (Johnston), we experimentally examined its foraging in different habitats to estimate indirect impacts of brown trout presence. The lakes in which G. auratus lives have recently become more turbid, so the experiment was also conducted under different turbidity levels. Laboratory feeding trials in which planktonic and epibenthic prey were simultaneously offered to G. auratus in the presence or absence of artificial macrophytes and at three turbidity levels (0, 50 and 100 NTU) revealed that its overall foraging success was unaffected by habitat complexity; however, in trials with artificial macrophytes, G. auratus consumed a greater proportion of planktonic prey than in the absence of artificial macrophytes. Neither overall foraging success nor prey selection by G. auratus was affected by high turbidity, indicating that water clarity does not appear to directly negatively impact its feeding. The switch in prey types would probably not be detrimental to G. auratus in the long term, and thus it appears that there is no substantial feeding cost associated with its increased use of complex habitats. It could, however, affect lower trophic levels in the lakes to which it is endemic.