Red-fingered Marsh Crab, Sesarma erythrodactyla

The Red-fingered Marsh Crab, Sesarma erythrodactyla, occurs in mangrove swamps, on river banks and in salt marshes. It can live in areas which have a low salinity, such as the upper reaches of rivers that are brackish.

Male Red-fingered Marsh Crabs may have a brilliant green shell, called a carapace, and orange and white coloured fingers, called chelae. The finger tips are brilliant red, which is where they get their common name.

The bright green colour of adult males is exactly the same colour as the fruits of the Grey Mangrove, Avicennia marina. Why is this so?

Here an adult male
Red-fingered Marsh Crab.

Female Red-fingered Marsh crabs are not as brightly coloured as the male crabs are. This may be for protective camouflage. Also see that they have much smaller chelae, or fingers.

This may affect what types of food it can eat, compared to the male. Might there be other resons for the difference in feeding claw size?

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References:

Davey, K. 1998. A Photographic Guide to Seashore Life of Australia.
New Holland press, Sydney.