The Bay Islands Reef System

Coral reefs are one of the most complex ecosystems on the planet, comparable in diversity to tropical rainforests. The Bay Islands [1] reef is particularly varied because of its location on the edge of the continental shelf, at the transition between shallow-water and deep-water habitats. Some 96 percent of all species of marine life known to inhabit the Caribbean — from tiny specks of glowing bioluminescence to the whale shark, the largest fish in the world — have been identified in the waters surrounding the Bay Islands. Divers and snorkelers flock here in droves to experience a dizzying assortment of fishes, sponges, anemones, worms, shellfish, rays, sea turtles, sharks, dolphins, and hard and soft corals.

What Is Coral?

Contrary to what many people understandably assume, coral is a stationary animal, not a plant. Each “branch” of coral is made up of hundreds or thousands of tiny flowerlike polyps. Polyps, thin-membraned invertebrates, compensate for their flimsy bodies by extracting calcium carbonate from the seawater and converting it into a brittle limestone skeleton. Through this continual, tireless construction process, the bizarre and beautiful undersea forests seen by divers and snorkelers are created, at a rate of about a centimeter per year.

Tiny, extended tentacles bring in food drifting by in the water, but the anchored coral polyps must supplement their intake by housing minuscule algae cells; these cells in turn produce nutrients for the polyps through photosynthesis. Because of this symbiotic relationship, coral always grows in relatively shallow waters, where the sun can penetrate. Reduced water clarity due to pollution or erosion from construction, agriculture, or deforestation can be fatal for coral, robbing the algae of the light needed to photosynthesize.

The main reef-building coral in shallow areas is leafy lettuce coral (Agaricia tenuifolia). This species virtually excludes other corals from many spur tops, growing in some areas to within 10 centimeters of the surface. In areas with greater wave energy, such as along the north sides of the islands, forests of treelike elkhorn coral (Acropora palmata) are common.

Star coral (Montastrea annularis), brain coral (Diploria spp.), boulder brain coral (Colpophylia natans), and elegant columns of pillar coral (Dendrogyra cylindrus) are often seen on the fore reef, at a depth of 10–15 meters.

Black coral is still found around the Bay Islands [1], usually in deeper waters on reef walls. Many shallower patches have been destroyed by jewelry-makers. In the water, black coral appears silver, only turning black when exposed to the air.

Fire coral, or hydrocoral, is not a true coral but a “battery of stinging nematocysts on tentacles of coral polyps,” as Paul Humann, author of a good three-volume reference on reef systems, describes it. Learn what fire coral looks like right away, and keep well clear of it — even a light brush can be painful.

Should you accidentally bump into fire coral, remember never to rub the affected area or wash it with fresh water or soap, as this can cause untriggered nematocysts to release their barbs. Two recommended treatments are vinegar or meat tenderizer, both of which immobilize the nematocysts.

The Reef

It’s often claimed that the Bay Islands [1] reef and the Belize reef system to the north together make up the second-longest reef in the world — after Australia’s Great Barrier Reef. Technically, the Bay Islands reef is distinct from the Belize reef — not only does a 3,000-meter-deep undersea trench separate the two, but they are different kinds of reef. The Belize system is a barrier reef, with the coral wall separated from shore by a lagoon at least a mile wide, while the Bay Islands system is a fringing reef, essentially beginning right from the shore. Sections of the north-side reef on the Bay Islands show characteristics of developing into a barrier reef in time but are still considered fringing reef.

Reef geography is generally the same on all three of the main islands. The north-side reef forms almost a complete wall, with only a few narrow passages allowing access to the shallow lagoon between the reef and the shore. The Guanaja [2] north-side reef is much farther offshore (about a mile, or 1.5 kilometers, in places) than on Utila [3] and Roatán [4]. From the reef crest, which sometimes almost breaks the surface, the reef slopes to a plateau at around 10 meters, then falls off the wall.

The south-side reef frequently starts literally at the water’s edge and slopes down at a more gentle grade to a depth of around 10–12 meters, when it hits the sheer reef wall bottoming on sand at around 30–40 meters. The southern reef is generally more broken up than the north, with channels, chutes, headlands, and cays. Sea mounts — hills of coral rising up off the ocean floor — and spur-and-groove coral ridges are common and are often the best places to see diverse sea life.

The Cayos Cochinos [5] reef system shares similar characteristics with the other islands, except it lacks steep drop-offs and lagoons on the north side.

The Health of the Reef

Generally speaking, the Bay Islands [1] reef is in pretty good shape, although certain high-impact areas are showing signs of damage from overdiving and decreasing water quality. According to a recent study, the Roatán [4] reef has 25–30 percent live coral cover (the rest covered by sand, sea grass, sponges, rubble, algae, dead coral, fire coral, etc.), a relatively healthy percentage compared to other Caribbean reefs.

Tourism development poses the most direct threat to the reef, since coastal and hillside construction generates runoff and other forms of water pollution. Degraded water quality leads to algae blooms, which steal sunlight, oxygen, and other nutrients from the coral, literally choking the reef to death. This threat is particularly severe on Roatán, where the island’s long central ridge is being carved up on all sides for roads and houses, while coastal wetlands, which filter runoff, are being filled in for construction. The reef off West Bay in Roatán [6] is particularly threatened, due to all the construction and tourist activity in the hills backing the beach.

While Guanaja [2] is quite hilly, construction on the main island is still limited, making runoff less serious. However, water pollution around Bonacca [7], Mangrove Bight [8], and Savanna Bight has damaged most of the reef surrounding those towns. Utila [3], mostly flat and still retaining much of its wetlands, does not face much erosion at the moment, but water pollution is a problem around East Harbour [9] and Pigeon Cay [10].

Coral bleaching occurs on the Bay Islands [1] reef, as it does on reefs all over the world. During these usually temporary events, higher water temperatures than normal cause the coral to expel the zooxanthellae (algae cells) that give coral its color pigments. The cells return when the sea temperature returns to its normal level, ideally 23–30°C (73–86°F). In 1998–1999, there was a global bleaching event, in part as a result of the warming of the world’s seas after the 1997–1998 El Niño phenomenon. Hurricane Mitch — so devastating above the water — helped spur the recovery of the Bay Islands reef from the prolonged bleaching episode by bringing up colder water from deeper in the ocean and cooling off the waters near the surface by as much as 3°C.

The proliferation of divers is beginning to take a toll on the reef; some oversaturated dive sites are closed off to allow for the coral to recover. These days, dive boats more regularly tie off on buoys instead of anchoring on the reef, but divers continue to bump and grab coral in spite of frequent warnings. Each brush with a piece of coral wipes off a defensive film covering the polyps, allowing bacteria to penetrate. Just one small gap can compromise the defenses of an entire coral colony. Think about that when you see the reef in front of West Bay Beach, Roatán [6], swarmed with thousands of cruise-ship visitors.

Black coral, formerly common around the Bay Islands [1], has been depleted in recent years by jewelry-makers, whose work can be seen in several local gift shops. For those tempted to buy a piece, remember it is illegal to take black coral into the United States.

Two websites with detailed research information on the Bay Island reef system are www.yale.edu/roatan/index.htm [11] and www.wfu.edu/~dkevans [12].