The Life and Times of the Manicou Crab
David Maitland, who teaches zoology at the University of Edinburgh, Scotland, seems a happy man. He and his team of researchers intend to uncover for science the total ecology of Tobago’s manicou crab (Pseudothelphusa garmani garmani).
"The lungs of the manicou crab are the most complex of any invertebrate. They are a pinnacle of evolution," he claims. And he should know. This is his third trip to Tobago to study the crabs. The first trip was in 1996, the second in 1997. And he plans to return in 1999. He is being assisted by dozens of "Millennium Fellows", other educators and people with conservation-related occupations, who have been selected and funded by the Royal Society of London. Earth Watch, the international conservation group, is funding David who is the project leader.
He explains, "We are looking at the total ecology of the manicou crab, how they interact with the plants and animals in the rainforest. It is a predator, feeding primarily on other animals, including other manicou crabs (they're cannibals), frogs, insects, even small snakes."
They are locally named "Manicou" crabs because the females carry their young in pouches on their undersides like the manicou (opossum). They live near, or in, fast moving, rocky streams from Mt. Irvine to Charlotteville. Unlike the blue crab, the manicou crab lives its entire life in fresh water. The female blue crab goes to the sea exactly at the time her eggs are about to hatch, usually in August, always on a night when the moon is full, to wash the larvae into the sea where they spend several weeks growing into miniature crabs. Then they come back to the land where they remain terrestrial.
The female manicou crab lays several hundred large eggs. All larval development takes place inside the egg. After they hatch, they live inside the female “pouch” until strong enough to fend for themselves.
David says, "Then the mother walks through the river letting them go, saying, ‘Bye-bye!’"
He is full of praise for Tobago and Tobagonians. He says, "The island smells different this trip, lots of fragrance and flower smells in the air. It's spectacular. The rivers are low for this time of year. Tobagonians are very courteous, like how they say, ‘I hope you enjoy the rest of your stay.’ How could we not?" He is excited by the fact that Tobago has the flora and fauna of South America.
He also praises Earth Watch. "Earth Watch," he says, "is the largest funder of this type of project. Biological surveys are not easily funded by conventional organisations."
David and his team are attaching radio transmitters to the backs of eleven crabs. They will plot the crabs’ travels for five weeks. Already they have been surprised to discover that a crab can walk 200 hundred metres in a night, both up the river and up the slope perpendicular to the river.
They are also learning a lot about the ecology of the rainforest, especially the animals. In the science of ecology, to know about one species you must also study all the living and non-living things that that species interacts with.
David will be writing articles and science papers throughout the project. These, he assures us, will be provided to Environment TOBAGO and the people of Tobago.
And one more thing: Baby manicou crabs eat mostly mosquito larvae. The more baby crabs, the fewer mosquitoes. He thinks the number of manicou crabs on the island is decreasing. Food for thought.