Where seen? This small crab with a bright
green or blue band on the face and red or dark claws are common in
some of our mangroves. It
was previously known as Chiromantes sp.
Features: Body width 2-3cm. Body
flat and squarish, legs flat with pointed tips. Pincers deep red.
Irridescent blue or green band across the face.
Two species commonly seen in our mangroves are Perisesarma eumolpe
with a dark upside down V-shape under the face-band and Perisesarma
indiarum with a bright upside-down V-shape under the face-band.
A study of these two species found that males of both species had
more intense blue facial bands, whereas green was more pronounced
in female facial bands. These colour differences may play a role in
sexual recognition within the species. Bigger females had more intense
blue in their facial bands, suggesting that s indicates of their maturity
(and possibly body condition). In large males, facial band colours
contrast strongly against the surrounding mudflat and may play an
important role in signalling to other males during territorial disputes
or competition for females.
These Perisesarma crabs eat sediment, leaves of various mangrove
trees, green algae and small invertebrates. The study suggests pigments
from their food may contribute to their colouration and thus could
be an honest signal of an individual's foraging ability, age or state
of health. Indeed, their study found the bands turned grey or black
when the crabs are dead. Females with eggs also had duller bands.
Another study found both P. eumolpe and P. indiarum
are mainly sediment grazers, but also feed on mangrove leaves and
roots and occasionally animals. Both crab species prefer Avicennia
alba leaves to other, locally common, mangrove species, i.e.,
A. officinalis, A. rumphiana, Rhizophora apiculata, Bruguiera gymnorhiza.
There is, however, no significant preference for leaves of differing
ages in the two species; and no difference in amount of fresh leaves
eaten by the two crab species.
The genus Perisesarma comprises one of the highest biomasses
of mangrove crabs and play an important ecological role. As they feed
on mangrove leaves, they recycle nutrients in the mangrove forest.
Quickly breaking down the leaves for others in the food chain to eat,
e.g., animals that eat the fragments left over by the crabs, what
comes out of the crab after it eats the leaves, and of course, the
Pulau Semakau, Mar 09
under the face-band.
Kranji Nature Trail, Apr 10
Pasir Ris, Jun 10
Kranji Nature Trail, Dec 10
Chek Jawa, Dec 09
sesarmine crabs on Singapore shores
crabs Ng, Peter K. L. & N. Sivasothi, 1999. A
Guide to the Mangroves of Singapore II (Animal Diversity).
Singapore Science Centre. 168 pp.
crabs (Episesarma and Chiromantes) Tan, Leo
W. H. & Ng, Peter K. L., 1988. A
Guide to Seashore Life. The Singapore Science Centre,
Singapore. 160 pp.
eumolpe (Decapoda: Sesarmidae) Face-banded sesarmine crab
by Wong Jinfa, 2012 on taxo4254.
ecology of two species of Perisesarma (Crustacea: Decapoda:
Brachyura: Sesarmidae) in Mandai Mangroves, Singapore" by Boon
Pei Ya, Darren C. J. Yeo, and Peter A. Todd in Journal of Crustacean
Biology, 28(3): 480-484, 2008 (Abstract
- "Inter- and
intra-specific variation in the facial colours of Perisesarma
eumolpe and Perisesarma indiarum (Crustacea: Brachyura:
Sesarmidae)" by H. Huang, P. A. Todd, D. C. J. Yeo in Hydrobiologia
(2008) 598:361-371 DOI 10.1007/s10750-007-9169-z (Abstract
- From the
wild shores of singapore blog
crabs perform their victory dance
Grace Chua, Straits Times 11 Jul 09.
- 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.
- 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.