Food resource variability in an Australian dryland river: evidence from the diet of two generalist native fish species

Abstract

To examine how food resource availability links with natural variation in primary productivity in the Moonie River, south-west Queensland, the diets of two native Australian fish species (Nematalosa erebi and Macquaria ambigua) were examined from fifteen waterholes in February, May and September 2006. N. erebi diets reflected strong ‘boom and bust’ patterns of food consumption, with high concentrations of benthic (non-filamentous) algae during boom (flow) times, moving to higher concentrations of filamentous algae and detritus during bust (no flow) periods. M. ambigua diets were primarily dominated by aquatic insects in all sampling periods. Although there was no clear ‘boom to bust’ pattern in relation to flow, M. ambigua secondary prey consumption revealed a compensatory switch between high energy prey (crustaceans) during more productive periods with terrestrial insects during less productive periods. The ability of both species of fish to switch from high to low concentrations of food quality under a variable environmental background allows them to persist through both high productive and low productive periods. This interaction between native biota and variable ‘boom’ and ‘bust’ conditions, and how changes to the natural hydrology will affect it is an important consideration of any future water resource development plans.

Subtle ‘boom and bust’ response of Macquaria ambigua to flooding in an Australian dryland river

“…See methods regarding missing data. The regression line indicates significant relationship opportunistically on Macrobrachium and zooplankton in the Moonie River (Sternberg et al 2008) and elsewhere (Pusey et al 2004;Balcombe et al 2005) so it is interesting to note that high prey availability during the study period was not reflected in a corresponding marked increase in the proximate body condition or biomass of M. ambigua. The lack of strong relationships is unexpected and suggests that whole body lipid content may be a rather crude surrogate for the physiological response of this species to increased food availability.…”

“…Adding to this, Collins and Anderson (1995) concluded that M. ambigua was, in relative terms, a "non-fatty fish". These observed low lipid levels may have masked any increases in body condition during the 'boom' period and may be an evolved trait in this species given the variability of food resources typical in these dryland systems Sternberg et al 2008).…”

“…Such traits include: high tolerance of harsh environmental conditions (Gehrke and Fielder 1988;Wager and Unmack 2000;, opportunistic spawning strategies (King et al 2003;Balcombe et al 2007) and adaptive feeding strategies Sternberg et al 2008). Species with these attributes can often reach high levels of abundance and biomass in large dryland rivers, where the productivity cycles of 'boom and bust' are mirrored by wide variations in fish abundance from 'boom' (high fish abundance) to 'bust' (low fish abundance).…”

“…Diet composition is spatially and temporally variable. Sternberg et al (2008) found that predation on higher energy prey items (such as macrocrustaceans and fish) varied with season and resource availability in response to 'boom and bust' cycles. Given that this species typically sits at the highest trophic position in dryland rivers (Pusey et al 2004), it is likely to be strongly dependant on the natural cycles of 'boom and bust' associated with flooding and drying.…”

Dietary niche differentiation of five sympatric species of Platycephalidae

“…The dietary plasticity and behaviour of generalist carnivores to switch between abundant prey suggest these species may be able to survive periods of variable prey abundances (Sternberg et al 2008). In contrast, the specialised diet of R. diversidens potentially makes this species more susceptible to significant changes in prey availability.…”