Coral reefs are large colonies of living animals. Reefs are similar to rainforests in that they support a surprisingly diverse range of species. One estimate is that they shelter 25% of all marine species while covering less than 0.1% of the ocean surface.
However, reefs are fragile ecosystems that are highly sensitive to water temperature. El Nino years are especially hard on coral, and global warming is a concern. Many once-colorful reefs are now a drab white; aside from the reduced aesthetics, bleached coral is likely to die. Estimates are that 10% of the world's coral reefs are dead, with another 60% threatened.
Pollution is a major problem for coral reefs. To highlight this, a part of the Roanoke Valley Reef is a "toxic reef" exhibit. Pieces in the Toxic Reef have been crocheted from plastic grocery bags with plastic spiral binding and various non-degradable plastics that are increasingly poisoning the Earth's water.
The Roanoke Valley Reef project has looked for ways to be eco-friendly. The recycling of yarn, pulled from old sweaters at yard sales, is one way to help the environment in general, and coral reefs in particular.