Copyright 1995 Jonathan Bird, O.R.G., Inc.
The Caribbean Sea. When many people think of the Caribbean, they think of the warm tropical beaches of a vacation paradise. But perhaps the greatest things to be found in the Caribbean are not on the beach, but underwater. This warm, tropical ocean boasts an incredible amount of marine life, taking many spectacular and usual forms. Join us as we journey Beneath The Caribbean, to discover the fascinating creatures which call this sea home.
The Caribbean Sea is much like every other tropical ocean in that it has very clear, blue water. The water appears blue due to the fact that the ocean absorbs all wavelengths of light very well, except for the short wavelengths of blue. The fact that tropical oceans are clear means that they are lacking in suspended sediment and plankton. This is in contrast to the popular misconception that tropical waters are very high in biological productivity. In fact, they are nearly sterile when compared with the cooler, plankton-rich temperate ocean regions, like the North Atlantic.
Plankton is the base of the food chain in all oceans. Because the tropical oceans are low in plankton, the creatures living in these regions have developed many unique techniques of capturing enough food to survive.
One very successful solution to the food problem in the tropical seas is the coral reef community. This complex community is centered around the coral reef itself. A coral reef is a living structure made up of thousands of tiny colonial animals called coral polyps. Each polyp is an individual animal with a mouth and a circle of tentacles used to capture prey. The tentacles are covered with microscopic stinging cells, called nematocysts. The stinging cells are used to subdue the prey, consisting of plankton and tiny bits of organic matter. On a night dive, a colony of brain coral devours the planktonic creatures attracted to our lights.
In order to build a reef, the coral polyps extract calcium from the seawater, and combine it with carbon (a by-product of their own respiration) to produce calcium carbonate, or limestone. This limestone is secreted layer by layer underneath the colony, to build up a skeleton for the coral. Every year, the coral reef grows a little larger, as it adds calcium carbonate to its skeleton.
The magic in a coral reef is not just the reef itself, but the importance it holds in the entire tropical ocean ecosystem. The coral reef is home for thousands of different creatures which rely upon it in one or more ways. Small fish hide in the coral, as it is usually the only place to hide. Like a crowded hotel, the reef fills to capacity with fish and invertebrates seeking to hide and make their nests. Sometimes the reef gets a head start with a shipwreck. When a ship sinks, the structure provides hiding places for fish. Slowly, over a long time, the ship breaks down and is covered with coral. After a hundred years or more, the ship may look like this old molasses steamer in the Bahamas. It barely looks like a wreck at all anymore, but the coral grows on the remains, and provides a sanctuary for many fish.
Small fish like these grunts stay close to the reef for protection. The abundance of small fish draws larger fish to the reef, where they circle around trying to catch an unwary lunch. Predators like barracudas spend the day circling the reef looking for food.
Some fish on the reef have developed fascinating ways to protect themselves. For example, the puffer inflates itself with water when it is threatened, thereby raising numerous pointy spikes. Most larger fish would find this to be a most unpleasant mouthful. The side-effect of blowing up like a balloon is a reduction in mobility and swimming speed. So, as soon as the threat is gone, the puffer deflates and swims away.
This hermit crab has a good technique for defense. On its shell, the crab has several anemones. Anemones are invertebrates closely related to coral, which have stinging tentacles, to capture food. Most anemones live their lives in one spot, anchored to the bottom, like this common Purple-tipped Anemone. The anemones on the hermit crab, however, live in a symbiotic relationship with the crab. By living on the crab's shell, the anemones gain mobility. Mobility gives the anemones the opportunity to feed on a wider variety of organisms than they would get by staying on the reef. In return, the crab gains the protection of the anemone's dangerous tentacles, and is free to roam the bottom with confidence.
One of the most common ways for fish and other creatures to gain protection on the reef is camouflage. The scorpionfish, which has evolved in such a way as to resemble an algae covered rock, is a good example. For defense, the scorpionfish has venomous spines along its back which can inject a predator with deadly venom.
Here's a fish that nearly everyone has heard about, but very few people have ever seen in person: the sea horse. It's hard to find a sea horse because it hides so well. The sea horse uses it's long tail to hold on to narrow sponges or soft corals, and blends in to look like a sponge itself. Since the sea horse can't swim very well, it relies upon this excellent camouflage to keep from being eaten by larger animals.
The strange-looking frogfish also looks like a sponge, but its camouflage has a different purpose. The frogfish pretends to be a sponge while, at the same time, flicking a lure back and forth in front of its mouth. This lure, called an illicium, is actually a modified part of the frogfish's dorsal fin, and is the key to getting dinner. When another creature mistakes the frogfish's illicium for a tidbit of food, the frogfish will engulf the creature in its enormous mouth. Frogfish can eat animals as large as themselves, but, fortunately, not as large as me!
Night on the reef. Most of the fish have found themselves hiding spots, and are fast asleep. But some creatures use the night to their advantage. The moray eel stays in its hole during the day, but comes out at night to search for a meal. The eel slithers in and out of little cracks and crevasses looking for small fish which have hidden for the night. The eel hopes to catch them off guard in their drowsy state. After a series of close calls, the eel stops to investigate our camera. As luck would have it, a drowsy damselfish wanders into the area at just the wrong time... and becomes the eel's dinner. The eel swallows the struggling fish whole!
Not only do fish hide in the reef, but larger animals do as well. This Loggerhead turtle is sleeping in a hole in the reef. Because the turtle is a reptile, like a snake or a lizard, he must surface to breathe periodically, but he still sleeps, hunts and mates underwater. For most of his life, he holds his breath. All marine turtles are endangered now, due to their slow reproductive capabilities and overhunting by man.
Marine turtles live in the water, but return to dry land to lay their eggs. Here, a Leatherback turtle, a member of the largest marine turtle species in the world, is digging her nest in the middle of the night. Once she has begun her digging, she is determined to finish her task and get back into the water, so she continues in spite of our flashlights. She digs a hole several feet deep and lays about 100 eggs. In 60 days, they will hatch into tiny replicas of herself and swim away into the sea. Unfortunately, this particular turtle has decided to nest on an eroding beach. In 60 days, there will be no sand where she is digging, and the eggs will perish. So Leatherback turtle researcher Peter Dutton and his team of volunteers are moving the eggs to a better location.
Interview with Peter Dutton:
"Okay, this turtle has nested on an eroding beach, and there won't be a beach here when the eggs hatch, so we are moving the eggs to a better location. As you can see, the eggs are flexible, unlike chicken eggs. They have a little dimple in them. And these eggs will bounce. I'm not going to demonstrate this, but they will bounce, because the eggs fall a considerable distance when the turtle is laying them. So what we're going to do is dig an identical nest here and re-bury the eggs. In two months they will hatch."
Two months later, just after sunset, the hatchlings begin to emerge from the nest. Just three inches long, the hatchlings head instinctively for the water. On their way, they are vulnerable to predation by birds and rodents, but the sea doesnt offer any greater security. Sharks and fish will threaten the hatchlings until they grow larger. Most will die, but some will survive, to carry on the legacy of their ancestors.
Looking very much like part of the coral, sponges are common on most Caribbean reefs. Many people do not realize that sponges are not plants, but living animals which must feed to survive. Although you can't tell by just looking at them, sponges feed constantly in a very efficient manner. Here, we demonstrate with a special non-toxic yellow dye. The outside of a sponge is covered with small pores called ostia, through which water is drawn from the sea. This water is pumped through the wall of the sponge by special pumping cells and finally is expelled through a larger hole called the osculum. While pumping the water, the sponge extracts minute particles of food, some as small as bacteria. Because of the fact that they can extract very small particles from the water, sponges are among natures most efficient filter-feeders.
Not all of the Caribbean is coral reef. An equally important part of the sea are the coastal mangrove forests. Mangroves are trees which live in shallow salt water, and put down roots which create an underwater labyrinth. In this maze, sponges and other stationary animals cling to the roots, and fish life flourishes. Mangroves are important because they serve as nurseries for young fish. The mangroves are relatively safe from the larger predators found out on the reef, so many smaller juvenile fish mature in the cover of the mangrove, and then later head out into the more dangerous coral reef areas in search of food.
Sometimes, manatees are found near mangroves. These large marine mammals can reach 12 feet in length and 3,000 pounds. Fortunately, they are very gentle, and eat only aquatic plants. Although these giants resemble whales and dolphins, they actually evolved separately, and it is believed that their closest living relative is not the whale, but the elephant! When Columbus first saw a manatee, he thought it was a mermaid, and not a very pretty one at that. In Columbuss time, manatees were common all over the Caribbean. Now, due to to pollution and accidents with deadly boat propellers, manatees are barely clinging to survival. Because manatees are slow swimmers, sometimes they cant get out of the way of speeding boats. This one was lucky. Although it has a terrible scar, it survived the accident. Only a few thousand manatees remain, and the population is getting smaller every year. Without immediate action, the manatee faces extinction by the year 2,000.
Out on the bottom near the reef, other kinds of creatures have adapted to life on the flat ocean floor. Cruising the bottom in pursuit of small creatures living in the sand, the Southern Stingray lives up to its name by carrying a venomous spine at the base of its tail. Although it is rare for the stingray to use this spine, the result can be a very serious wound. Stingrays are fish, but they have no swim bladders, so they sink. In order to deal with the problem, they have become bottom dwellers.
Another bottom dweller is the flounder, a flat fish which camouflages itself to match the color of the bottom. Works pretty well, doesn't it? If the flounder doesn't move, it is nearly undetectable. Because both of the flounder's eyes are located on the same side of its head, it can see potential predators before they see the flounder.
Unfortunately for the flounder, the dolphin doesn't hunt by eyesight alone. Dolphins have good eyesight, but they see better with sound than with their eyes. They have a form of sonar called echolocation, which enables them to see for great distances underwater. This is accomplished by making clicking sounds which travel through the water and bounce off of distant objects. By listening carefully to the sounds bouncing back at them, the animals can detect objects which are too far away to be seen with their eyes, or are buried in the sand. In fact, one of the ways these Spotted Dolphins feed is by using echolocation to find fish and invertebrates hidden in the sand. Then, they stun the prey with very loud sounds, and eat it. Because they have such advanced means of finding prey, very little time is actually spent feeding. Instead, the dolphins spend a lot of their time playing. Sometimes, even playing with people.
In the open ocean, dolphins play in the tropical sunshine. Spotted dolphins are common in the Caribbean. These were filmed near Grand Bahama Island. Dolphins are social animals, which means that they tend to stay together in groups. These groups, called pods, can range from 2 individuals up to 30 or 40. Unfortunately for us, since we are so slow by comparison, the dolphins get bored with people fairly quickly, and swim off together, leaving us behind.
For the dolphin, the manatee and the other creatures we have met, the Caribbean Sea is a backyard playground. This is their home, where they live their lives and bring up their young. To us, the Caribbean is a warm-water vacation paradise. But the Caribbean is more than just warm water and beaches. The Caribbean is an ecosystem centered around the coral reef. In this coral reef community, some creatures use the reef for shelter, some use it for food, and others seek the animals living near the reef. Without the coral reef, life would be scarce in these nutrient poor waters. The reef community is an extremely complex ecosystem, and is important not just for the creatures of the seas, but for us as well. In this modern age where we have the ability to change the environment with our actions, it is our responsibility to preserve and protect this delicate ecosystem thriving Beneath the Caribbean.