The Mitten Crab - Another crab found in streams...and in restaurants. Actually, that is not quite true...Whilst many species of crabs are edible such as the famous 'Mitten crab' Eriocheir sinensis, which is found in Chinese waters, our local Mitten Crab is actually another species of similar appearance, Eriocheir japonicus, and is not very tasty. Here it is pictured below, in a stream just above ShaKokMei in SaiKung, about 2km from the coast. You can see its hairy "mittens" quick clearly.
Also known as the "Hairy-clawed crab", I mention the location near the coast as this crab, whilst spending most of its life in freshwater, must return to the sea to release its eggs, which hatch into planktonic larvae. And this is a really quite fascinating journey, so read on:- After feeding and maturing for 4-5 years, the crabs migrate downstream in late summer, and then attain sexual maturity in the tidal estuaries. After mating, the females continue on into the sea, overwintering in deeper waters, returning to brackish water in the spring to hatch their eggs. After their development as larvae, the tiny juvenile crabs slowly but surely move upstream into fresh water pools, where they can be seen feeding, thus completing their life journey....before it all starts again. SaiKung is an ideal area for them as it as the types of estuaries suitable for the mitten crab; ie large brackish waters for the larva to develop in, and large shallow waters for the growth of the juvenile crabs. Not many animals can live in such different environments, so have a think about this: 1) Eggs require pure salt water to mature. 2) Larvae hatch from the eggs in brackish waters. 3) The larvae gradually move from brackish water to fresh water. 4) The final stage of the larvae is the megalopa, which is 3-4mm in length. 5) The megalopa then develop into small mitten crabs in the freshwater, and up the stream they go! And just think of the journey that these creatures make, even as tiny little crabs!
The mitten crab diet is omnivorous. Their main prey consists of worms, mussels, snails, dead organic material, and other small crustaceans and fish. All this activity is in contrast to the more terrestrial and solely freshwater crab that I blogged about yesterday, pictured here to show the difference.