Online Snorkel Trips



Put on your mask, fins and snorkel, and let’s go on a make-believe exploration in a Virgin Islands National Park coral reef! But first, let’s learn a little bit about what a coral reef is, and how to snorkel responsibly in one of the world's most important ecosystems.

Leinster Bay St John
Leinster Bay, St. John, USVI

Susanna Pershern

Coral reefs are one of the world's most complicated ecosystems; they are found in warm, clear, tropical seas around the world. (This picture shows Australia's Great Barrier Reef.) Some scientists think that 1 million kinds of animals and plants live in the world's coral reefs, but only about 10 percent of the life has been identified; wow! There are fish, sea stars, snails, sponge animals, seaweed, crabs, bristly worms...and of course corals.

underwater picture of living elkhorn coral

NOAA's Florida Keys NMS

Have you ever heard of the guessing game “Animal, Vegetable, Mineral” or sometimes called “20 Questions?” It's fun, and doesn't need any equipment; just your creativity.

The game starts by one person being the starter. He (or she!) thinks of some thing, like "dog," but keeps the thing secret. Now it's the job of the other people to take turns asking questions to the starter person that he can answer by saying only "yes" or "no" to the question. The first person to ask a question usually starts with, “Is the word you're thinking about an animal, a vegetable or a mineral?”-- meaning: is the word an animal, a plant or is it non-living, like a rock? After that, other people take turns asking questions to narrow down what the thing could be. The first person to guess the thing correctly in 20 questions or less wins!

The picture shows living elkhorn coral. Soooooooo, what's a coral?

closeup  of two coral polyps in the expanded state, each showing a mouth surrounded by about a dozen tentacles


Soooooo, as a part of a coral reef, what is a coral? -- animal, vegetable or mineral?

Well guess what?! Coral is all three! To begin with, a coral is mostly an animal called a polyp, and it eats things. The polyp tentacles capture small living things from sea water, and then stuff the food into the polyp's mouth.

This is a microscopic view of many greenish, single-celled zooxanthellae, which live in the skin cells of corals.


A coral polyp is also sort of a plant. How would you like to have lunch by going outdoors and standing in the sun for half an hour while spinach in your skin photosynthesized to make food for you?! That’s what corals do; they have tiny plant cells (called zooxanthellae…zo-zan-thel-ee) living in their skin that make food for the coral. But zooxanthellae don’t look anything like spinach; each one is just a single cell; so gazillions of them live inside almost every coral cell, giving coral its color. And some zooxanthellae can make 90% of the food a coral needs; wow!
an underwater picture of an elkhorn coral skeleton

NOAA Center for Coastal Monitoring & Assessment

Finally, coral is sort of a rock, but it’s a living rock. As the coral polyp grows, it makes more and more polyps, all joined together to become a coral colony. By chemical action, each coral polyp takes the minerals of calcium and carbonate out of seawater to make a hard, limestone outside skeleton for the colony. Each little polyp sits at the top of the limestone rock in a little cup, and its body connects to all the other polyps in its coral colony. The colony is all one connected happy family! The picture is an elkhorn coral skeleton.


At the heart of a big coral colony is limestone. The top layer of the colony is living animal polyps. Inside the animal polyps’ skin cells are plant-like zooxanthellae. Coral is pretty amazing...and it's ALIVE! But it grows very, very slowly. It might take a coral colony 10 long years to grow to be the size of a coin, like a U.S. quarter (1" or 2.5 cm); wow!

underwater picture showing 2 snorkelers; one is behaving irresponsibly by standing on coral

NOAA, courtesy of Ziggy Livnat

OK; now that we know what coral reefs and coral are, come along on a snorkel trip in Virgin Islands National Park. But remember, corals are ALIVE! Don't swim too close to a coral colony and accidentally knock off a piece that might be waaaaay older than you are. How would you like it if your hand broke off? And of course don't stand on coral!

SOS means "Stand On Sand." What's the person doing wrong in this picture?

If you do at least one of these two snorkel trips, you can print yourself a Virgin Islands National Park SOS Snorkeler Certificate, and show it to the Ranger at our Visitor Center when you visit our Park!

Online Snorkel Trip: Corals, Sponges and Creepy Crawlies
Online Snorkel Trip: Fish and Turtles


Last updated: March 23, 2020

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