Pollution is not only directly affecting coral reefs, but is indirectly also making life difficult for them. Sunlight is essential for coral reefs. Symbiotic algae called zooxanthellae living in the corals photosynthesise to produce carbohydrates and oxygen that the corals use to make reef-building calcium carbonate. If waters become less transparent then the entire process of photosynthesis gets disrupted. Researchers from the Biglow Laboratory for Ocean Sciences in Maine, USA, found that some reefs in the Florida Keys are getting barely enough sunlight to sustain themselves. (New Scientist, March 23, 2002, Vol 173, No 2331, p14).