07 February 2011

Horseshoe crabs at Kranji: what are they up to?

Jerome spotted this pair of Mangrove horseshoe crabs (Carcinoscorpius rotundicauda) at Kranji on Sunday. Males often 'hitch a ride' on top of the females. This pair was stuck among the pneumatophores (breathing roots). Perhaps stranded by the outgoing tide?
Were these horseshoe crabs getting ready to mate and lay eggs? What do our horseshoe crabs get up to? The Nature Society (Singapore) (NSS) recently published an article about their efforts to find out.

In an article in Nature News Jan-Feb 2011 (pdf), J. Vanitha shares the effort to tag horseshoe crabs at Kranji.
Led by Dr Hsu Chia Chi and Dr Lesley Cartwright-Taylor, the NSS has been regularly studying horseshoe crabs at Kranji for some time now. They have decided to tag the animals "to understand the crabs’ traveling habits, homing instincts and maybe even locate their spawning sites."

From the article:
On 20 November 2010, transmitters were fixed onto eight adult horseshoe crabs (four males and four females). Of these, two males and two females were released back at the site of capture at the Mandai Mudflats. The remaining four crabs were released at Lim Chu Kang jetty about five kilometers away, to see if they had homing instincts to find their way back to Kranji.

Receivers will be picking up the signals from the crabs’ transmitters. They can store the date and time of the detected signal as well as the identity of the crab. Periodically, the collected data will be downloaded to find out where these signals are coming from.

Results will be published at a later date.

We look forward to finding out more about what our horseshore crabs are up to!

See also Population structure and breeding pattern of the mangrove horseshoe crab Carcinoscorpius rotundicauda in Singapore by Lesley Cartwright-Taylor*, Julian Lee, Chia Chi Hsu (pdf)

Here's some blog posts about the tagging of the horseshoe crabs and one of the trips on the NSS study at Kranji by misspegasus. And other posts by Grass Tales and by Itchy Fingers.

Fiona also did a study of horseshoe crabs at Kranji: more on her project blog and project report (pdf).

Unfortunately, abandoned driftnets take a heavy toll on the horseshoe crabs in Kranji. Here's an account of the rescue of 300 of them on the Habitatnews blog.


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