Deep sea dibs

Monday 31 May 2010

When it comes to the worm, the crab is always early  

In the dark, never-ending abyss of the sea live myriad creatures: small marine animals called macrofauna which include snails, clams, worms and “creatures no bigger than a pencil eraser” to crabs, starfish and sea urchins. Craig McClain from the National Evolutionary and Synthesis Center with James Barry from the Monterey Bay Aquarium Research Institute in usa dived within reach of these communities to see what drives their ecology.

“Deep-sea biodiversity rivals that of a tropical rainforest or coral reef. Over a mere 100 metres you can get a gradient of food that radically alters the types of organisms present,” said McClain. With a depth mimicking that of Arizona’s Grand Canyon, the Monterey canyon was chosen as the location.

A remote-operated vehicle equipped with video and sampling equipment was lowered on the canyon bed. Its journey was recorded on video and samples were collected from the canyon floor. About 5,280 individual organisms across 197 species were identified. The rover also found a constant influx of food flowing down the canyon walls onto the seabed. But despite the extra nutrients, the small sediment-dwellers were smaller and even less diverse than those on surface.

Bigger organisms eat most of the food before it reaches the seabed, leaving the benthic creatures hungry. The animals can sense an influx and they rush to the walls for a grab. The food’s journey to the seafloor is cut short as it ends in a crab or a sea urchin’s gut, said the study in the April issue of Ecology. “It is not just individual organisms that are important; it is how they are linked by the food webs. Removal of any part of the web that evolved over tens of millions of years is likely to have unforeseen consequences,” said McClain. Carbon sequestration of the seas, for example, may disrupt food webs.
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“Indirect human activities like eutrophication have already started their damage. Nitrogen fertilizer consumption in South Asia increased by a factor of 50 over the past few decades. This is expected to bring changes in benthic ecology of coastal ecosystems including the ‘Swatch of No Ground’, a Bay of Bengal canyon,” said S Naqvi, biogeochemist at the National Institute of Oceanography in Goa.

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