Spatial and temporal changes of three prey-fish assemblage structure in a hypersaline lagoon: the Coorong, South Australia

Abstract

Estuaries and coastal lagoons are the dynamic interface among marine, freshwater and terrestrial environments. The Coorong, an Australian wetland, has been ecologically degraded by protracted drought and subsequent low freshwater flow, and transformed into a hyper-saline lagoon system. The Coorong consists of the North and South lagoons and connects to the Southern Ocean through a narrow channel at Murray Estuary. The present study investigated spatiotemporal variation of three primary prey-fish assemblage in the Murray Estuary and Coorong. Spatial change in prey-fish assemblage was detected, but temporal variation was not obvious. Prey-fish assemblage was dominated by greater abundance of small-mouth hardyhead (Atherinosoma microstoma) in the South Lagoon. There was low abundance of sandy sprat (Hyperlophus vittatus) and Tamar goby (Afurcagobius tamarensis) in North Lagoon, and complete absence of both species in South Lagoon. The spatial variation in the distribution of prey-fish assemblage was attributed to elevated salinity gradients (Murray Estuary: 2–30; North Lagoon: 11–75; and South Lagoon: 40–85). The change of prey-fish assemblage is mainly driven by the salinity variation in the Murray Estuary and Coorong. The present study has improved our understanding on the dynamics of small-bodied prey-fish assemblage and key environmental factors regulating fish distribution in the Murray Estuary and Coorong.