Overfish ing, especially for sport fish such as sailfish, can dwindle local fisheries.

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Like all coral islands, keys are the remnant s of ancient coral reef s, and many keys are still ringed by healthy reef ecosystem s.

Over time, the top of a coral reef is expose d to the surface.

Waves and wind slowly transport sediment, sand, shells, and even living organisms to the exposed reefs depositional node.

A depositional node is simply a part of the reef where currents are less likely to erode the material deposited there.

Usually, depositional nodes are at the reefs highest elevation.

The nutrient -rich sand and sediment often support coconut palms and other plants.

Sturdy mangrove forests often thrive in the coastal areas of keys.

The shallow, shadowed waters of these mangrove forests offer habitats for shorebirds, such as egrets and herons.

Coral reefs that often surround keys provide one of the most biodiverse habitat s on the planet.

Coral reefs boast an array of fish, sponges, marine mammal s, and crustacean s, in addition to the corals that support the ecosystem.

Native animal species in keys are often smaller than their mainland counterparts.

Key deer, for instance, are an endangered species native to the Florida Keys.

Key deer are related to white-tailed deer, but adapted to their small, isolated environment by evolving to grow less than half the size of their North American cousins.

The soil and sediment that support such diverse, healthy ecosystems can also support agriculture.

In addition to coconuts, key residents often harvest mangoes, dates, guavas, and other tropical fruit s.

Most livestock on keys, usually pigs, are introduced species.

Agriculture is not a strong economic activity on keys, however.

Tropical waters surrounding keys include grouper and sharks, and deeper waters include populations of sailfish, tuna, and other large species.

Keys white sand beaches and tropical waters make them popular vacation spots.

The Florida Keys, Caribbean keys (often called cays) and the keys of Australias Great Barrier Reef draw millions of tourists every year.

The same elements that make keys so inviting can also make them vulnerable.

Thousands of tourists and a growing service-based economy (including hotels, charter boats, and fishing opportunities) can stress the key environment.

Define Keys