Close-up they look like flowers. When in 1723, naturalist Jean Andre' Peyssonel proposed that corals might be animals, he was functionally expelled from the French Academy of Sciences. Today we know he was right. Individually, most corals measure less than half an inch across, yet collectively they have built the largest organic structures on earth. The Great Barrier Reef stretches over 1,250 miles along Australia's eastern shore, and the Palancar reef bordering Mexico, Belize, and Honduras is nearly as large.
Tropical seas are nearly devoid of nutrients, which is one reason the water is usually clear.
Yet reefs which thrive within them are among the planet's most prolific living systems, veritable oases in oceanic deserts. How so much life could be sustained on so little food remained one of the greatest scientific mysteries until 1929 when researcher C. M. Yonge unraveled one of the most marvelous co-operative relationships in the animal kingdom. These algae are doing exactly what plants do best. This is precisely what a coral animal needs to grow. The more sunlight the better.