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mangrove challenge


Photo of a water mouse
A Water Mouse attacks a Red-fingered Marsh Crab claw.
Photo: Bruce Cowell, QM

Photo of a Red-fingered Marsh Crab
The Red-fingered Marsh Crab lives in the upper part of the intertidal zone. It is the favourite food of the Water Mouse.
Photo: QM

The Water Mouse is a very rare creature: a carnivorous mouse. Water Mice can swim, but never catch and kill prey in the water. Instead, they prefer to set out from their nests on the banks behind the mangrove intertidal zone at night and follow the retreating high tide, scouring the prop roots of Rhizophora and the surface of the mud for food.

Middens, the remains of meals, show that crabs are important prey of the Water Mouse. The animal eats grapsid crabs such as the Red-fingered Marsh Crab, Parasesarma erythrodactyla, and the Purple and Cream Shore Crab, Helice leachii. These crabs live in the upper part of the intertidal zone, breathe out of water, and hide in burrows at low tide. The Water Mouse attacks its crab prey with precision, biting off the eyes, tearing off the claws then extracting flesh from the crab's carapace, first cutting the softer undersurface with its teeth. It also eats a variety of other invertebrates, mainly bivalve and slug molluscs and marine flatworms, found in mangrove pools or under logs. Queensland Museum scientist Dr Steve Van Dyck has hypothesised that this varied diet may be the reason the distribution of the Water Mouse stops around the Gold Coast, the southernmost region where this high diversity of mangrove invertebrates is found.

The Water Mouse moves frenetically through mangroves looking for food. Using radio-tracking devices scientists have found that foraging males move as far as 2.9 km in one night. They use the same corridors, and prefer to stay under cover of the aerial roots of trees rather than forage in the open spaces of Avicennia forests. The Water Mouse has a keen sense of smell: smelly chemicals (called pheromones) made in its anal glands and added to droppings persist even after high tides and enable it to navigate through mangroves. Sometimes, if it catches a large prey item such as a crab, a Water Mouse will eat it and rest for several hours in a hollow log.

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