Explore Geology
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Buck Island Reef

National Monument

Virgin Islands

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park geology subheading
Underwater photo of diver at Buck Island Reef
Buck Island Reef National Monument, Virgin Islands

The Coral Reef
Of all the reef residents, the corals have the most extraordinary habits; these are the architects, the builders, and the landlords of the reef. Ranging in size from a pinhead to a raindrop, billions of tiny master builders, called polyps, erect the dazzling array of reef forms that give quarter for all other life in the coral community. As architects of the reef, they must follow natural, but nonetheless strict, "building codes" that keep them:

  • within tolerances of light,
  • temperature,
  • salinity,
  • oxygen,
  • motion,
  • depth, and
  • firmness of the base on which they build.
World geography even dictates site selection for coral structures.

Usually associated with the shallow waters of offshore tropical islands, coral reefs are seldom found farther than 22° north or south of the equator. They occur only off the east coasts of the world's continents, where prevailing winds and the earth's rotation push tropical waters north and south toward the poles. Reef builders reject, as substandard, building sites along deeper western continental shores; there cold upwelling currents move toward the equator and preclude their growth.

Here in the Caribbean, waters are clear, maximum light is available, and temperatures meet polypean standards—rarely falling below 20°C (68°F). Currents move gently, bringing the plankton—microscopic animals and plants—on which the nocturnally-feeding polyps subsist. In these waters too, polyps find solid foundations at acceptable depths. Reefs seldom develop in water deeper than 45 to 60 meters (150 to 200 feet), and soft or shifting bottoms have poor coral formations or none at all.

Construction of a typical aquatic housing project begins when the free-swimming coral larva attaches itself to some firm surface, becomes a full-fledged polyp, and begins secreting its own limy exterior skeleton. This single polyp and all its many descendants, building on one another, budding new members as they go, erect their communal skeleton outward and upward toward the all-important rays of the sun. Colony after colony in hundreds of shapes and sizes ultimately create the reefs that decorate the ocean floor—spires, trees, shrubs, stone-hard staghorns, huge boulders that appear to be designed after the cortex of a monstrous brain belonging to some supersized being. Each shape and design represents a species of coral.

The larger, more rigid structures become the "buildings" of the coral community. Among them, surrounding them, are the plantlike shapes of near relatives—the gorgonians, sea whips, and sea fans. Only a small percentage of growing things in the reef community are true plants. Reef ecology is one in which the animals far outnumber the plants—the reverse of lush land communities where plants outnumber animals.

Even as the polyps erect their dwellings, multi-colored fishes and other marine creatures already are moving in. These residents comprise a second category of reef inhabitants. To the still backdrop of coralline shapes, they add life and motion and color. The third major group of creatures at the reef are those which come to feed upon its inhabitants. Sharks, snappers, and barracudas, among others, cruise slowly among the corals, seeking the opportunity to flash toward unwary prey. For every creature there is a role to fulfill and a purpose unique to its own kind.

The overall effect is one of pure fantasy. A world so sensate, so unmercifully beautiful, could not have been created by the richest of imaginations. In the coral reef, the gifts of life and beauty are concentrated as they are nowhere else in nature.

From Pastureland to Parkland: Buck Island's History
Buck Island, beautiful as it is, bears the scars of long habitation. Since the 1750s, the island has been used for a residence, and for agriculture, pasturage, and lumbering. In 1948 Buck Island became a park and was administered by the Virgin Islands Government; in 1961 the area was transferred to the National Park Service.

When colonists first set eye on Buck Island in the 1770s, it was covered with Lignumvitae trees,locally called Pokholdt trees. The island took its name from these trees. Corrupted by usage, the name changed from "Pocken-Eyland" (Dutch) to "Bocken" and finally to "Buck". The latter two names refer to goats that were pastured on the island beginning in the 1750s. Sometime during the 19th century, the Lignumvitae trees were cut for lumber—incidentally creating abundant pasture for the island's goats. When rapid regrowth of the forest threatened the goats in the early 1900s, the eastern half of the island was burned over repeatedly.

Another animal associated with man—the rat— indirectly created a separate ecological problem in the early 1900s. Bubonic plague, which is spread by rats, was epidemic in Puerto Rico at that time. Declaring war on rats, officials introduced mongooses in many areas, including Buck Island. Because mongooses forage during the day, and rats are nocturnal animals, the strategy failed. The mongooses prey primarily on the island's native birds and reptiles, and the rats continue to survive.

Despite the continued presence of some introduced animals, Buck Island belongs more to nature today than at any time in its recent history. The return to nature began with the elimination of the goats in the 1950s. Overgrazing had by that time reduced the island to a more-or-less desert like appearance. As the vegetation returned at a quickening pace, Buck Island again became home to a variety of native species. The island is now one of the important Caribbean nesting sites left where the pesticide-ridden brown pelican is still producing live young.

Safety Tips for Sea and Shore

  • The intense tropical sunlight of this region is more likely to cause you discomfort and pain than any other hazard here. Protect yourself from the sun by using plenty of waterproof sun-blocking lotion. Wear a hat, a shirt, and other protective clothing when practical.

  • Always swim or snorkel with at least one other person. In an emergency, this "buddy system" can provide immediate help. If you haven't snorkeled before, be sure to practice in shallow water before daring the reef.

  • While enjoying the waters off Buck Island don't forget that some hazards do exist. The most dangerous "creatures" you will encounter are boats; watch for them when swimming or snorkeling. Swim quickly out of high traffic areas such as anchorage and mooring sites.

  • Avoid touching corals; most have sharp surfaces and some sting.

  • If you encounter a barracuda don't be alarmed; consider yourself fortunate to have seen this fascinating reef inhabitant. Although a barracuda may follow you, it means no harm, so don't hurt yourself in a frantic attempt to escape. However never feed a barracuda. Feeding could arouse aggressive behavior from this many-toothed predator, or the fish could have trouble distinguishing between the food and your fingers.

  • Onshore, several of Buck Island's plants are poisonous to touch or eat. Do not handle any plant that you cannot positively identify as harmless.

Protecting Your Park

    A few regulations are necessary to preserve the natural values of this park area. Following these rules during your visit will make it possible for you and others to enjoy the park another time.

  • Fires must be confined to picnic area grills or your own personal self-contained stove or grill. No open fires are allowed.

  • Camping is not permitted on Buck Island, but you can camp aboard your boat offshore.

  • Plants and animals in the park area are protected. The collection, harassment, or destruction of any plant or animal is prohibited. Seashell collecting is restricted; contact a park ranger for more information. The Marine Garden, a nearly pristine reef and lagoon area, is closed to all fishing and shellfishing.

  • Coral formations are fragile; avoid anchoring in them. Touching or standing on coral is also destructive.


park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A general photo album for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.



geologic research subheading

For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.



selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

Currently, we do not have a listing for any park-specific geology education programs or activities.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www.nature.nps.gov/Geology/parks/buis/index.cfm   I  Email: Webmaster
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