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Plankton bloom off the coast of Vancouver Island and the state of Washington is visible from space. ((NASA))

Scientists continue to track a mysterious bloom swirling along the west coast of Vancouver Island.

Satellite images posted on NASA's web site show a blue-green cloud of phytoplankton, tiny plantsat the base of the marine food chain thathelp sustain ocean ecosystems.

A bloom means there are a lot of nutrients present for fish, federal fisheries department scientists said.

There are more than 100 species of plankton that could be causing the bloom, said David Cassis, who studies plankton at the University of British Columbia.

Organisms that carry paralytic shellfish-poisoning toxin, known as red tide, don't have a shell, said Angelica Pena of the Institute of Ocean Sciences in Sidney, B.C.

In this case, the bloom appears to consist mainly of the shelled phytoplankton coccolithophore, scientists at the institute said. The single-celled organisms are shaped like hubcaps surrounded with a microscopic plating of limestone scales.

When trillions of coccolithophores are present, the water turns an opaque turquoise.

Warm weather and bright sunshine are ideal conditions for the organisms. Scientists are concerned global warming could spur more blooms.

Over the long term, the species helps remove carbon dioxide, a greenhouse gas that contributes to climate change, by locking it up in their scales. The scales then form sediment at the bottom of the ocean.

However, in the short term the organisms generate carbon dioxide that can escape into the atmosphere, according to NASA's Earth Observatory web site.

The bloom is concentrated about 15 kilometres off the island's west shore.

Marine biologists say the only way to be certain the phytoplankton is harmful is to test it, but provincial biologists say budget restrictions will prevent testing until the bloom comes within a kilometre of land. They're using satellite images to track the bloom's movements.

Researchers believethe bloomcould last up to two weeks, unless a large storm breaks itup sooner.