River to landscape connections and biodiversity

18 September 2015

Hub research has strengthened our understanding of the factors underpinning high levels of aquatic biodiversity and productivity in the floodplains of Kakadu National Park.

Lead by Griffith University’s Professor Stuart Bunn, the evidence produced by this project can be used to predict how natural and manmade changes to ecosystem connectivity might impact aquatic biodiversity within Kakadu, as well as other tropical floodplain systems.

The project considered several key questions:

Where is the water on the floodplain?

The extent, depth, duration and connectivity of flooding across floodplains in the Alligator Rivers Region of Kakadu National Park were analysed using satellite images from 1985 to 2011, combined with field-sampled water level data. These results were summarized into a single map, which indicates that the East Alligator, West Alligator and Wildman River have the largest areas of long duration flooding.

What is the most important food source in the food web?

Stable isotope analysis of primary food sources revealed what different animals have been eating over their life, and where. The most important primary food source supporting aquatic food webs was epiphytic algae, which is the film of algae that grows over the submerged stems of plants and other surfaces.

Are there hotspots of productivity on floodplains?

The research found that backswamps were the most productive areas, as they have the longest duration of flooding and are deep enough to exclude vertical grasses, which limit epiphytic algae production for much of the year. Important backswamp areas occur in Nourlangie, Yellow Water, and Boggy Plain regions of the South Alligator floodplain, and the upper Magela Creek floodplain.

How are animals accessing the floodplain resources?

Acoustic and radio tracking of barramundi and salmon catfish found both species used inundated floodplain habitats extensively throughout the wet season and returned to their home billabong once the water began to recede. This demonstrates the importance of connectivity between landscapes and that fish migration is a key process of moving energy from floodplains sources to main channels.

You can read the full outcomes of the research, in the final report, Tropical floodplain food webs – connectivity and hotspots.

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