Biology: Blue Desert

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Whitsunday Islands.

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When you see the image above, "desert" is probably the last word that comes to mind. Tropical waters are warm, clear and full of life right?

Wrong. In general tropical waters, near the equator, have less marine life than the colder temperate waters to the north and south. Here is why.

Seasons create differences in temperature throughout the year. These temperature changes cause the deep and surface water to mix. The mixing brings nutrients to the surface allowing phytoplankton to grow. This phytoplankton, being at the bottom of the food chain, feeds the rest of the food chain.With out it most marine life can't survive.

The the problem with the tropics is that with out distinguished seasons the surface water and the deep water don't mix. Without any nutrients left in the surface water, all the nutrients lie bellow 492 feet (150 m) to a depth too dark for phytoplankton to grow, leaving most of the tropical waters with less life then temperate waters.

Coastal upwellings and coral reefs act as oases in the vast blue desert. Coral reefs accumulate and recycle nutrients and in coastal upwellings deep seawater moves up to the surface.

Sources: Oceans: A Visual Guide by Stephen Hutchinson and Lawrence E. Hawkins
Photo: Wikipedia