learn only 3 things about them ...
They are edible and among our favourite seafood.
They can swim fast using their paddle-shaped last legs.
do not survive long out of water.
seen? Flower crabs are among our favourite seafood! It
is commonly seen on many of our shores, especially the Northern shores
and those with seaweeds and seagrasses. But it is not easy to spot.
If trapped in a pool at low tide, it buries itself in the sand or
mud. Besides the larger adults, there are also lots of smaller juvenile
flower crabs hiding among the seagrass and seaweeds.
Features: Body width 5-7cm to
about 20cm. Body fan shaped with nine 'teeth' on the sides, the last
tooth enlarged into a protruding spike. The eyes are not very far
apart. Males usually have bright blue legs and claws, females tend
to be dull green and brown. And excellent swimmer, the flower crab's
last pair of legs are paddle-shaped and rotate like propellers. It
is a fully marine crab and cannot live long out of water. The long
pincers are armed with sharp spines which snags swimming creatures.
Flowering crabs: Some flower crabs
may have a 'garden' of various living seaweed and barnacles
growing on their bodies, pincers and legs. These crabs are usually
those infected by a parasitic
barnacle (Thompsonia sp.)
What does it eat? The flower crab
is a predator. In other parts of the world, it has been reported to
eat mostly slow moving, bottom-dwelling creatures such as snails and
clams, and worms. It may also eat fish, shrimps and other crabs.
The difference between boys and girls: Male
flower crabs have long pincers, twice to three times longer than their
bodies are wide. Males are also more decorative, with blue markings
and attractive patterns on their bodies. Females are better camouflaged
in dull green and brown. The male's abdomen is more narrow forming
a pointed triangular shape, while the female's is broader as she uses
the abdomen to carry her eggs.
Moult ‘n’ mate: Like many other
crabs, Flower crabs can only mate just after the female moults. Often,
a male is seen protectively holding on to a female. He does this because
she is either just about to moult; or he has just mated with her and
wants to make sure no other male gets to her before her shell hardens.
The male transfers his sperm into a special receptacle in the female.
When the female is ready to spawn, she will use his sperm to fertilise
her eggs. The fertilised eggs are attached as a big mass (called a
sponge) to her abdomen where she cares for them until they hatch.
They hatch into free-swimming larvae that drift with the plankton,
changing into yet another form before settling down and developing
into miniature flower crabs.
Role in the habitat: Flower crabs
are predators. In turn, they are eaten by animals higher up in the
Human uses: Flower crabs are edible
and a favourite dish for many Singaporeans. They are caught with nets
or baited traps. In Western Australia, they are an important fishery
resource with 740 tonnes, valued at around $2.2 million, harvested
Changi, Jun 05
Flower crab (top)
its moulted shell (bottom)
Sentosa, Jul 04
Mating crabs, male on top.
Pulau Sekudu, Jun 05
Those infected with parasitic
tend to be covered with seaweeds.
Pulau Sekudu, Apr 06
Buried in sand.
Tuas, Oct 10
Tiny ones are also seen. This one is
hardly bigger than a Button snail.
Changi, Apr 05
crabs on Singapore shores
- Ng, Peter
K. L. and Daniele Guinot and Peter J. F. Davie, 2008. Systema
Brachyurorum: Part 1. An annotated checklist of extant Brachyuran
crabs of the world. The Raffles Bulletin of Zoology. Supplement
No. 17, 31 Jan 2008. 286 pp. (Online
PDF on the Raffles Bulletin of Zoology website).
- Chou, L.
M., 1998. A
Guide to the Coral Reef Life of Singapore. Singapore Science
Centre. 128 pages.
- Lim, S.,
P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life
and Times of Labrador Beach. Division of Biology, School of
Science, Nanyang Technological University & Department of Zoology,
the National University of Singapore. 160 pp.
- Jones Diana
S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of
Australian Waters. Reed New Holland. 224 pp.
- Edward E.
Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.