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We all know the Earth’s surface is two-thirds water, most of which constitutes the world’s oceans. But did you know that 25 percent of marine life depends directly on coral reefs? Like cities, coral reefs cover a disproportionately small area—only 1 percent of total marine habitat—but these bustling underwater metropolises are home to a richness of life that rivals tropical rainforests.

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Sometimes mistaken for plants with their branchlike features and often colorful pigments, corals are actually miniature sea anemone-like animals. The animal part of a coral, called a polyp, consists of a head and a stomach. From the head extend tiny toxic tentacles that are used like harpoons to spear equally tiny floating plants and animals, called plankton. Hard corals, which you are probably most familiar with, grow cup-shaped calcium carbonate skeletons around their soft bodies, creating massive reefs over hundreds or even thousands of years. Indeed, some large coral reefs are like ancient underwater cities—only instead of buried rubble and debris, these cities are loaded with life.

A school of yellow fish, about the size of an adult's hand, swim among fan-like clumps of coral.

As corals build upward and outward, ocean inhabitants from shrimp to sharks crowd reefs in search of a new home or good meal.

Aside from being prime seabed realty, coral reefs also support people. They are nurseries for a quarter of the ocean’s fish species, many of which we like to eat. Coral reefs also protect coastal cities from large storms, acting like breakwaters, and are an increasingly important resource for developing new medicines.

Unfortunately, our cities on land pose serious risks to the coral cities in the ocean. Overfishing, careless tourism, pollution and destructive fishing practices are a few causes for concern. In fact, a quarter of the world’s corals are already damaged, possibly beyond repair. Thinking about our reliance on seafood for a source of protein, consider this—bottom-trawling, a fishing practice that drags a weighted 400-foot-long net across the seafloor, can pulverize a coral reef. Every year the world’s bottom-trawling fleet devastates an area of ocean bottom twice the size of the contiguous United States. That’s a grim outlook for so valued an ecosystem.

Fortunately, organizations like Shedd are helping to protect corals. In 2011, our expert aquarists helped rescue more than 1,500 coral colonies and fragments from a deteriorating reef in the Florida Keys National Marine Sanctuary. Shedd is also successfully propagating corals in tightly controlled habitats, using high-tech water filtration to create the unique environmental conditions required to grow corals.

You can help, too! Next time you order seafood at a restaurant or grocery store, ask where it came from and how it was caught. Was it caught using bottom-trawl nets, which are known for habitat destruction and bycatch (fishes and other untargeted marine life unintentionally caught and killed in nets)? Or was it caught using a more sustainable fishing method, like mid-water trawling, or poll and line, which have less impact on the environment and are more selective in terms of catch? Your consumer choices can help save the coral cities of the world!

Reid Bogert, former Great Lakes sustainability team member