EnviroMatters Magazine Spr-Sum 2024-25

underwater worlds collide Where Beneath the surface of the Brisbane River at Colleges Crossing a fascinating overlap happens where fresh and salt water meet.

Environment Matters | 7

Colleges Crossing is the interface between two very different ecosystems. Upstream, the upper and mid reaches of the Brisbane River provide freshwater environments. Downstream, the lower reaches provide saltwater estuarine habitat. Underwater at Colleges Crossing you will find fish that exclusively live in fresh or salt water swimming side by side – a very special sight! Freshwater species include: Crimson spotted rainbowfish Eel-Tailed catfish Fly-Specked hardyhead Diadromous species (rely on both fresh and saltwater during lifecycle) include:

Estuarine species include: Bream Bull shark Diamondfish Flathead Silver biddy

Australian bass Long-finned eel Sea mullet

Mouth almighty Pacific blue eye

SEE FOR YOURSELF This video by Peter

Hansler from Pete’s Fishing and Under Water Videos shows the life underwater at Colleges Crossing.

Grassy fields for fish In the video of Colleges Crossing you can see Vallisneria, also known as eelgrass. This important plant grows in dense mats underwater in shallow, gently flowing streams, providing a ‘grass cover’ that stabilises sediment, and provides shelter for small and juvenile fish. It is the favourite food of the vulnerable Queensland lungfish, which also uses this plant to attach its fertilised eggs. Lungfish fry (baby fish) rely on Vallisneria for shelter and nutrition. These ribbon-like plants were once common across South-East Queensland, including at Colleges Crossing. However large or frequent floods rip large areas of Vallisneria out of the riverbed and remove the propagules (seeds or reproductive bits of plants). Restoration of Vallisneria fields in the Brisbane River, by transplanting nursery-grown stock, seeks to improve the river health and habitat for species such as lungfish.