Can drifting invertebrates meet the energy requirements of drift-feeding fish? A case study on Galaxias fasciatus

Resource availability and quality determine the distribution and community structure of animals in ecosystems. However, the balance between energy supply and energy consumption of species has received little attention because of the difficulty of estimating these factors. We measured the carrying capacity of a stream ecosystem in relation to the metabolic demands of Banded Kokopu (Galaxias fasciatus), a drift-feeding fish, to investigate the proportion of their energy budget met by the supply of their primary prey, drifting invertebrates. We sampled drifting invertebrates from multiple pools in 2 freshwater streams once a month over 1 y and measured their energy content. We used the energy content of individual invertebrates to estimate the total energy available in the form of drifting invertebrates in each pool. We measured fish O2 consumption rate (mg O2 kg1 h1) and converted it to metabolic demand (cal/h). Drifting aquatic invertebrates alone appear to be insufficient to meet Banded Kokopu e...