Subterranean Fishes of the World

7054

2025

Freshwater Biology

70

Intact riparian vegetation plays an important role in the energetics of freshwater ecosystems. Plant and animal biomass from the riparian zone may be directly consumed by freshwater organisms without intermediary processing by microbial or metazoan communities. This study examined the extent and importance of such direct consumption by Australian freshwater fishes. We assembled a data set that spanned the Australian continent and examined the extent of terrestrial contributions to freshwater fish diets for 137 species (i.e., approximately one half of Australia's fish fauna). Using a range of multivariate methods we examined variation in reliance on terrestrial material (leaves, fruit, invertebrates and vertebrates) between species and families and between different regions of Australia, particularly focussing on differences between temperate and tropical Australia. We also examined whether particular aspects of morphology were related to increased consumption of terrestrially-derived material. Overall, terrestrial invertebrates contributed 10% or more of the diet of about one quarter of all species and families examined. Most families contained at least one species for which consumption of terrestrial invertebrates was high (> 20%) but only two families, Galaxiidae and Melanotaeniidae, exhibited consistently high consumption across most species. Terrestrial vegetation, principally fruit, contributed 10% or more of the diet in three species from two families only (Terapontidae and Ariidae). There was little regional variation in reliance on terrestrial invertebrates as a food source, but species in south-western Western Australia consistently consumed more than did species elsewhere. Frugivory, in contrast, was significantly more common in the wet-dry tropical northern Australia as reported elsewhere for other tropical regions. Australian freshwater fishes appear to rely more on terrestrial invertebrates than do freshwater fishes elsewhere although data is largely lacking to make broader comparisons with other continents. Morphological correlates with the consumption of terrestrial material were individually and collectively limited, but species with a pelagic habit and an upturned (supraterminal) mouth consumed significantly more such material than did species within other habit/mouth orientation combinations. The present study further confirms the importance of the riparian zone to lotic ecosystem function with direct contributions of terrestrially derived material contributing significantly to the diet of many species and of some families in particular. Although data is lacking for large-scale (i.e., continental) assessments of the importance of terrestrial subsidies to aquatic food webs elsewhere, riparian inputs appear especially important in the Australian context and especially in regions characterised by low primary productivity. Loss or degradation of riparian vegetation can pose a threat to freshwater fishes at a variety of spatial scales. The present study provides a baseline for further studies of the importance of terrestrially-derived material at large spatial scales.

3