Ecological observations in Singapore

My interest towards the hairy crab Pilumnus vespertilio (Fabricius, 1793) was piqued after the Labrador rocky shore field trip, especially after I got to hold the tiny crab in my palm!

Look just how tiny it is! (From http://tidechaser.blogspot.com/2010/02/semakau-walk-on-29-jan-2010.html)

The appearance of the hairy crab is bizarre, with long, rough brown hairs covering its body, giving it a furry and teddy bear-like appearance (Gopalakrishnakone, 1990). These hairs help to trap sediments and aid them in camouflaging. With a body width of 3-5cm, these mild-mannered hairy crabs are small enough to fit easily into our palms (as seen from the picture above).

The hairy crab is often found lurking on rocky and coral rubble areas, especially in areas abundant in Sargassum seaweed (Tan, 1988). It feeds on seaweed, larger algae during low tide and even toxic zoanthids (colonial anemones). Hence, this makes the crab itself mildly poisonous.

Nibbling on Seaweeds! (From http://www.wildsingapore.com/wildfacts/crustacea/crab/pilumnidae/pilumnidae.htm)

During full moon low tides whereby the crabs are most active, mating and copuation would usually occur. Reproductive behaviours exhibited by the male hairy crabs would include searching and waiting at the female’s burrow entrance. One interesting fact to note is that these males have a preferred choice of female as well! The males would station themselves outside a potential partner’s burrow entrance (whereby mating usually takes place), preventing other males from copulating (Kyomo, 1999).

Likewise, the females would also demonstrate preferences towards the males. If they have accepted the waiting male, they would emerge from their burrow and copulation would then take place. If not, the poor male hairy crab would just have to “wait till desperation”! (Kyomo, 1999)

References:

Gopalakrishnakone, P., 1990. A Colour Guide to Dangerous Animals. Singapore University Press, Singapore. p. 110 and 111.

Kyomo, J., 2001. Reproductive Behaviour of the Play-Dead Hairy Pilumnus Vespertilio (Crustacea: Brachyura: Pilumnidae) with respect to Carapace Size. Bulletin of Marine Science, 68(1): 37–46

“ Hairy Crabs Family Pilumnidae,” Ria Tan. Wild Fact Sheets, Dec 2008, URL: http://www.wildsingapore.com/wildfacts/crustacea/crab/pilumnidae/pilumnidae.htm (accessed on 12 April 2010)

“Semakau Walk on 29 Jan 2010,” by Ron Yeo. The Tide Chaser blog, 2 Feb 2010. URL: http://tidechaser.blogspot.com/2010/02/semakau-walk-on-29-jan-2010.html (accessed on 12 April 2010).

“Labrador’s all time favourite crab – the hairy crab,” by N. Sivasothi. Habitatnews, 8 June 2005. URL: http://habitatnews.nus.edu.sg/news/labrador/blog/2005/06/labradors-all-time-favourite-crab.html (accessed on 12 April 2010).

Tan, L. W. H. & Ng, P. K L., 1988. A Guide to Seashore Life. Singapore Science Centre, Singapore, p. 160. Online version available.