10 April 2010

Christmas Island: crabs and other curious creatures

Yesterday I attended a talk by Tan Heok Hui about the recent Raffles Museum of Biodiversity Research expedition to this marvellous island of treasures.
Prof Peter Ng gives us, as usual, a colourful introduction.

A somewhat remote island, it is widely considered the Galapagos of the Indian Ocean. Many of the flora and fauna on Christmas Island are endemic, i.e., only found on this island!
The most famous of the amazing creatures on this island are the Christmas island red crabs (Gecarcoidea natalis). These crabs are terrestrial, but have to go to the sea to release their larvae. During the mating season, countless numbers of crabs move in the most spectacular crab migration on the planet, towards the sea. To avoid running them over, special tunnels under the road are constructed.
All kinds of different signs are put up to alert motorists. Many are drawn by kids.
Here's some Singaporeans being really careful about avoiding the red crabs crossing a road. Heok Hui tells us some islanders carefully sweep the crabs off the road with a broom before driving through.
Eventually, the females reach the waters' edge to release their larvae. Unfortunately, being terrestrial crabs, they can't swim. If they accidentally fall off, they drown! A few months later, there is a reverse migration of the young crabs back onto land!
Heok Hui shared lots of other photos and details of these amazing crabs. And after the talk, there was much discussion about when is the best time to go. Here is more information about the crabs and their migration on the Australian Department of Environment website.

Heok Hui shared lots of background about the island's history and natural history. The island used to be part of Singapore before it was transferred by the British Colonial government to Australia in 1957. Currently, more than half of the island is protected as a National Park, and it has many spectacular and special natural features.
For example, although the island has no coastal mangroves, it has mangroves at 50m above sea level! These are at Hosnie's Spring and comprise Bruguiera gymnorhiza and Bruguiera sexangula that are probably remnant mangroves stranded there as the sea levels fell many thousands of years ago. The trees here grow to a humungous 30-40m tall! Discovered only in the 1980's, it is a habitat unique to Christmas island and not surprisingly, it is a Ramsar Wetlands site of international importance.
There are a bewildering variety of other fascinating habitats on the island (broadly, 12 habitats in total according to the Australian Department of Enviroment website). The intrepid Museum expedition members explore some of the challenging habitats, such as caves!
They also went diving to access underwater caves with awesome stalactite formations!
Where they discovered some crustaceans new to science!
Diving the fantastic reefs of Christmas Island, they find all kinds of critters.
Like these crustaceans that live in feather stars!
And tiny little hermit crabs that take over abandoned tubeworm holes in living corals. With awesome photos!
Even among the coral rubble, there were amazing crabs!
They also saw sharks, stingrays, dolphins and sea turtles.
And a whale shark too!
They also checked out the intertidal shores. Here's Prof Peter on the shore and some of the crabs found there.
While here's Tan Swee Hee carefully extracting a teeny tiny crab (the topmost one in the photos) which had oddly position eyes that reminds Heok Hui of a hammerhead shark!
Even the sandy shores reveals all kinds of crabs!
While other crabs were found living with these limpet-like sea urchins that live on the rocky shore!
Other curious crustaceans include the world's largest hermit crabs. The Robber or Coconut crab (Birgus latro) grows to a huge size and adults don't bother to stick their butts into shells. Heok Hui shares that every kilo of hermit crab is about equivalent to 10 years of growth. So a 4 kilo hermit crab is really old! He shared lots of other fascinating stories about them.
There's also a lovely blue form of this crab that is common on Christmas Island only.
I learnt that unlike marine crabs that mate only when the female is moulting, these shameless blue crabs don't need to wait.
Besides crustaceans, Heok Hui also shared lots of photos and stories about other endemic and special animals of Christmas Island. Such as these cute little birds.
Apparently this bird is so special that birders come all the way to Christmas Island just to see them, and leave immediately after checking it off their list.
While in these pirates of the seas, the males have a huge red inflatable pouch that is, as usual with weird male excesses, used to attract females.
The animals of Christmas Island are not fearful of humans. Heok Hui shared how this insect eating bird suddenly landed on the shoulder of an islander who was mowing his lawn. Apparently the fearless bird was using the man as a lookout post for insects fleeing from the mowing machine!
Sadly, many of Christmas Island's special creatures are threatened. Some like the tiny little bat in the photo are feared to be already extinct.
These native rats of Christmas Island are already extinct, probably displaced by alien invasive rats that came in with humans.
Alien invasives are indeed a problem. The Yellow crazy ants are most famous for affecting populations of among others, the Christmas Island red crabs. Sadly, they are believed to have been introduced from either Singapore or Malaysia. Other invasives include giant centipedes, the Giant african land snails and feral cats.
Besides the island's natural history, Heok Hui also shared about life on Christmas Island. Having once been under Singapore administration, it has features which may be familiar to us. Such as these flats reminiscent of the old flats seen in Singapore!
There are only about 2,000 residents on the island, and life is very peaceful. There are no traffic lights and the single roundabout is a major feature. Not only for traffic but also as the spot where signs are put up about what's going on in the island.
The main industry on Christmas Island used to be phosphate mining. This has damaged some parts of the island. But the Australians are trying to rehabilitate these areas.
This RMBR expedition is not the first at Christmas Island. It follows one done much earlier and hoped to find out the status of the fauna there. Heok Hui also shared some photos of the island then and now, and it seems things are pretty much unchanged.
Here's a photo of the expedition team. Wow, they sure managed to do a lot with a small team!
And a great photo of Prof Peter which suits his latest role in raising funds for the new museum!
Heok Hui covered lots and lots more with fascinating stories and gorgeous photos that my feeble sneaky cam can't do justice.

After the talk, Tan Seng Chye from the Ministry of Foreign Affairs shared fascinating stories of his childhood on Christmas Island. He saw whales at the island, and went out in small boats on the sea where porpoises would come up and allow him to pat them!
Heok Hui also brought along some of the specimens they collected. The Robber crab sure is huge!
Talks by the RMBR are fascinating! Do come for the upcoming talks "Zoological Explorations in Singapore" on 16 Apr (Fri). An evening dedicated to conserving Singapore's biodiversity, it will cover latest studies on our mousdeer, civet cats, banded leaf monkeys and freshwater crabs.


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