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June 28, 2010 | By:  Nature Education
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Episode 18: The Bleaching of Colorful Coral Reefs

In today's episode, Dr. Randi Rotjan of the New England Aquarium speaks with Adam about coral reefs, specifically the basis for their brilliant colors — the result of a symbiotic relationship between corals and algae. Within the sheltering tissue of the coral invertebrate animal lives plant-like algae whose photosynthesizing pigments come in a variety of colors, and whose energy production the coral relies on. However, when coral is stressed by man-made pollutants and human activities in ocean waters, this symbiotic relationship is threatened. The algae withdraw, leaving the animal in danger of dying without its symbiotic partner; with no algae inside, coral becomes white and colorless, a phenomenon called “coral bleaching.” This visual evidence of stressed coral reefs reflects how sensitive coral animals are to small changes in the marine ecosystem, and is a warning sign of complete destruction in a reef. In fact, 30% of coral reefs worldwide have already been destroyed, so understanding how to bring back a near-dead “bleached” coral reef is of great interest to scientists like Dr. Rotjan. Hopeful research results from a large Pacific marine reserve called the Phoenix Islands suggest that coral reefs have the capacity to rebound from a sickly white state to a colorful symbiotic one with restored algae, if negative human influences are kept at bay. Join Adam as he learns what coral is made of, and what efforts ocean biologists are making to understand, revive, and strengthen coral reefs. [06:36]

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