Interdecadal comparison of the trophic interactions among abundant species of fish in a permanently-open estuary in south-western Australia

Madeline I Wallington

Estuaries are important coastal ecosystems, as they contain great abundance in faunal species, but also serve as an important location for many human civilizations. However, they are also considered to be highly variable environments, with this variability having a large influence on faunal communities within them. This is witnessed through competition between species, as species cannot sustainably coexist if their ecological niches do not differ in at least one dimension. This gives rise to the different trophic niches taken up by abundant species within an estuarine environment. This study follows research conducted on the trophic interactions of abundant fish fauna in the Swan-Canning Estuary. Differences in dietary composition were investigated for three abundant members of the fish fauna; Acanthopagrus butcheri, Leptatherina wallacei, and Pseudogobius olorum, who uptake differing feeding niches. Dietary samples were collected from the Swan Canning Estuary within 2022/2023, and also from a previous study conducted in 2011, through seine netting. Samples were collected in both the Upper Swan and Upper Canning Rivers, as well as within each season. Dietary samples were analysed visually and percentage volumetric contribution of each dietary item to the total stomach content was estimated through the use of the PRIMERv7 software, employing multivariate analyses. This study revealed significant inter- and intraspecific differences in dietary composition, influenced by mouth morphology and trophic niche. Acanthopagrus butcheri consumed bivalves, crustaceans, and larger prey, Leptatherina wallacei favoured insects and arthropods, and Pseudogobius olorum ingested crustaceans and insects, with all species having a notable contribution of detritus to their diets. These differences were linked to variations in local benthic macroinvertebrate abundance and opportunistic feeding strategies, which showed significant spatial and seasonal differences. One notable example of the seasonality of prey items was observed in the diets of L. wallacei, with aquatic insects contributing significantly higher volumes to the diet in spring compared to other seasons. Interdecadal comparison revealed that all species in the Swan River region ingested a higher volume of amphipods in this study, whereas during the study by Linke (2011), stomachs contained more polychaetes. In the Canning River, Linke (2011) observed the diets to contain a higher volume of amphipods and polychaetes compared to 2022/2023 diets. These dietary changes may reflect differences in anthropogenic disturbance levels, as crustaceans, specifically amphipods are intolerant of anthropogenic disturbance, where polychaetes thrive in disturbed areas. This may suggest that the Upper Swan River in 2011 was significantly disturbed compared to now, with the Canning River showing the opposite trend. Given the relationship between benthic macroinvertebrate abundance and estuarine health, future research could explore whether analysing the dietary composition of abundant fish species can help monitor and protect these environments, mitigating harmful human impacts.

Interdecadal comparison of the trophic interactions among abundant species of fish in a permanently-open estuary in south-western Australia

Files and links (1)

Abstract

Details

Metrics