Copyright 1995 Jonathan Bird/Oceanic Research Group, Inc.
All Rights Reserved
The South Pacific Ocean. When many people think of the South Pacific, they think of exotic tropical locations and beautiful blue water. But perhaps the greatest things to be found in the south pacific are under water. This warm, tropical ocean boasts an incredible amount of marine life, taking many spectacular forms. Join us as we journey Beneath The South Pacific, to discover the fascinating creatures which call this ocean home.
The Pacific ocean is a huge expanse of seawater. It is the largest of the oceans, and also the oldest, as it was the first ocean to form. Therefore, the creatures in the Pacific have been around for a long time. This long evolution time has produced many unique species found nowhere else in the world. For example, while the Caribbean and Atlantic oceans together have under 100 species of reef-building corals, the pacific has over 500.
The tropical south Pacific is much like every other tropical ocean region in that it has very clear, blue water. The water appears blue due to the fact that that the ocean absorbs all wavelengths of light very well, except for the short wavelengths of blue. The other, longer wavelengths, like reds, oranges, and yellows are absorbed by the water.
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 seas when compared with the cooler, plankton-rich temperate ocean regions, like the North Pacific.
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.
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 the reef in one or more ways. Small fish hide in the coral, as it is usually the only place to hide. Away from the reef, there is just flat sand, offering no protection to most fish. Like a crowded hotel, the reef fills to capacity with fish and invertebrates seeking to hide and make their nests.
Small fish like these Blue Chromis stay close to the reef for protection. Even just a tiny coral colony like this one attracts marine life. When a threat advances towards the fish, they quickly retreat into the coral. When the threat has left, they resume their search for the larger plankton on which they survive.
The abundance of small fish draws larger fish to the reef, where they circle around trying to catch an unwary lunch. Here a huge school of fusalier swarm around the reef, searching for smaller fish, like Blue Chromis, to eat. Jacks, small tuna, and many other kinds of medium sized fish all spend the day circling the reef looking for food.
The larger fish draw sharks, nature's ultimate predator. These animals occupy the top of the food chain, feeding on the sick and weak, thereby keeping the gene pools strong. We frequently see many species of sharks on the reef, especially the Gray Reef shark. Although they are more than capable of eating humans, most sharks prefer to seek meals which are easier to obtain. Although they are curious of our film team, they are not aggressive.
Sharks are opportunistic feeders, and will readily accept dead fish from us, in lieu of live food. Sharks beautiful and graceful animals which are smarter than they are usually given credit for. Moreover, without sharks, the food chain would have no top predators to keep the medium sized fish populations in check. For this and other reasons, sharks are extremely important in the ocean food chain.
Skates and rays are close relatives of the sharks. Sharks, skates and rays are all cartilaginous fish, having a skeleton made of cartilage rather than bone. Because all cartilaginous fish lack swim bladders, they are heavier than water and tend to sink. The largest ray in the world, the Manta Ray, keeps from sinking by flying through the water with giant strokes of its enormous wings. Once known as the Devil Fish, Pacific Islanders used to believe that this tremendous animal would viciously attack people. Little did they know that even though the Manta Ray can reach 25 feet across, it feeds exclusively by filtering tiny planktonic animals from the water. It is completely harmless. Although smaller than the Manta Ray, the Eagle Ray also uses its wing-like pectoral fins to fly through the water, and stay up off of the bottom.
In contrast to the rays, the skates have opted to allow themselves to sink. So they spend their lives living near the bottom, searching for food like worms and mollusks, which live in the bottom. When the need arises to escape predators, the Blue-Spotted Stingray simply digs in and hides. How does it accomplish this task? Watch carefully...
Instead of blending into the sand, the stonefish uses the reef by blending in to the coral and waiting for prey to come along. Stonefish are among the most venomous fish in the world. The spines along its back are used to inject venom into an attacker. Many islanders around the Pacific say that the pain caused by such a wound in a human often causes the victim to commit suicide. The sting can be (and frequently is) fatal.
The lionfish is a close relative of the stonefish, and is also found in the tropical Pacific. Due to its beautiful coloration and ornate feather-like fins, the lionfish has become a popular aquarium fish throughout the world. But beware, for like the stonefish, the lionfish can sting, causing great pain. Each pointy projection on the lionfish is a deadly venom syringe.
Moray eels are also common reef inhabitants. Although the moray may look menacing with its toothy grin, in fact it is quite docile, and actually rather curious of our cameras. This species of moray, the Spotted Moray, probably uses its coral-like camouflage pattern to sneak up on prey .
Fish are not the only animals which live near the reef for protection. Many invertebrates are found here as well. One such invertebrate is the anemone. Anemones are actually close relatives of coral, having tentacles with stinging nematocysts to capture prey. But unlike coral, anemones are solitary, living not in colonies, but all by themselves. Additionally, anemones have larger tentacles and are able to capture larger prey, some as large as fish. But what keeps this huge anemone from capturing this fish? This is an anemonefish, which lives in a symbiotic relationship with the anemone. The fish has a special mucous coating on its body making it immune to the anemone's sting. The mucous also tells the anemone not to sting the fish. In exchange for the privilege of living in the protective tentacles of the anemone, safe from danger, the colorful anemonefish attracts other fish to the anemone, where they are captured and eaten by the anemone. The anemonefish then gets to share in the meal. Taking full advantage of its hosts protection, the anemonefish even uses the anemone to protect its eggs. The eggs are carefully laid on the reef, under the edge of the anemone. Covered by the deadly tentacles, few fish would dare try to eat them. Periodically, the male parent anemonefish goes to the eggs and checks on them, fanning them free of sediments. Strangely, all anemonefish are born as males. As they mature, some will metamorphose into females, while others will remain male. With anemonefish, the females are the dominant sex.
Not too far from the anemonefish we find a giant Tridacna clam. The Tridacna clam eats by filtering tiny bits of organic matter from the water using its two siphons. The incurrent siphon sucks in the water, where it is filtered through a sieve. After extracting food and oxygen from the water, the clam finally expels it through the excurrent siphon. For protection, the clam can close surprisingly quickly when it senses a reduction in light caused by the shadow of a predator.
These giant clams, which can reach 3 feet across, are rare on many reefs due to heavy harvesting by clam fishermen. Ironically, although a large clam may yield a hundred pounds of meat, very little of it is edible to humans. Tridacna clams are protected from fishing in many areas and, due to their ever decreasing numbers, Tridacna clam farming is becoming more and more common. There is now a Tridacna clam farm on the tiny Pacific island of Kosrae!
Although present in large numbers on the reef, it is usually quite difficult to find an octopus. The octopus hides in a hole in the reef, safe from being seen, but gives away the location of his den with the remains of the crabs on which he survives. The octopus is actually closely related to the giant clam. These two seemingly unrelated creatures are both mollusks, though their body forms are strikingly different. The octopus, a shy animal, usually sleeps by day, hidden in its den, and searches for food at night. Sometimes, however, we can find an insomniac octopus out for a stroll during the day. Octopods are masters of camouflage, using color-changing cells called chromatophores in their skin to alter their dominant skin pigments in less than a second. This allows the octopus to blend in with virtually any background, either to sneak up upon prey, or simply to evade detection. One of the most amazing things about octopods is their intelligence. Octopods are probably the smartest invertebrates in the world. Unlike most ocean creatures which are afraid of divers and hide from them, the octopus is genuinely curious. Just looking isn't enough. This octopus wants to know what we feel like too. The animal is gentle, yet it clamps down with many suction cups, forming a tight grip. It's a good thing that they are friendly, because if this little mollusk didn't want to let go, we'd have a serious problem!
Clinging to the edge of the reef is an animal commonly mistaken for a plant. This is the crinoid, or feather star. A relative of the sea star, the crinoid uses its feather-like arms to capture drifting plankton and organic matter. It holds onto the reef using a set of appendages which act like fingers. Crinoids try to position themselves in good places to catch plankton, but if they pick a bad spot, they can always move, walking slowly on those tiny fingers. These beautiful and fragile creatures come in many colors from golden yellows to deep black.
Perhaps no creature better fits the echinoderm phylum than the crown-of-thorns sea star. The term echinoderm means "spiny-skinned" and includes all sea stars, sea cucumbers, crinoids and sea urchins. If ever an animal had spiny skin, the crown-of thorns certainly does. The venomous spines of the animal protect it from being eaten by all but a few specialized predators.
The crown-of-thorns is a major predator of coral. It eats the coral polyps alive, leaving just a dead, white skeleton behind. In many areas of the Great Barrier Reef, Crown-of-Thorns sea star outbreaks have decimated the coral. The Crown-of-thorns holds onto the reef with its hundreds of sucker-equipped tube feet.
Another echinoderm, which looks nothing like the crown-of-thorns, is the pincushion star, or sea biscuit. A sea biscuit is basically a sea urchin with no spines, looking a bit like a basketball. These enormous echinoderms search the reef for algae which they scrape from the reef using a mouth with scraping teeth on its underside.
For many animals, the reef provides not only a place to live, but food to eat. The parrotfish relies upon the reef for its meals. Like real parrots, parrotfish have beaks. However, the parrotfish beak is designed for biting hard coral. The parrotfish lives on the algae growing on dead portions of the reef. The parrotfish gnaws at the algae and ends up eating a lot of the coral's limestone skeleton. This limestone is pulverized by chewing and is eventually passed completely through the parrotfish's digestive tract, to be deposited as sand on the bottom. Believe it or not, one of the main sources of tropical sand is parrotfish! A single parrotfish produces on the order of 1000 pounds of sand per year! At night, the parrotfish creates a bubble of mucous in which it sleeps. It can take nearly an hour to create this bubble, and the bubbles exact purpose is not known. It is suspected that the bubble hides the scent of the parrotfish so that it cannot be detected by nocturnal predators such as sharks.
The damselfish also eats algae growing on dead portions of the reef. However, unlike the parrotfish, the damselfish actually farms the algae. The damselfish finds a nice area of the reef, usually among the bases of staghorn coral, and stakes a claim. It then chases other fish away from its turf and nurtures the growth of the algae. As the algae grows, the damselfish keeps it in check by eating it. The damselfish will challenge anything which enters its section of the reef, including our divers' cameras.
Only a few feet from the reef, on the sandy bottom, we find another echinoderm, the sea cucumber. This sea cucumber eats sand in order to get at the microscopic animals and plants living within it. When disturbed or threatened, the sea cucumber protects itself by releasing long, sticky strands of poisonous tissue, to incapacitate a predator. These strands are actually part of the sea cucumber's respiratory system. South Pacific islanders have long used sea cucumbers to catch fish in tide pools by stunning them with the poison from the sea cucumber.
Sharing the sand with the sea cucumber, we find small fish called gobies and their room mate, the blind shrimp. The gobies and the shrimp live in a symbiotic relationship, each helping the other to survive. The shrimp maintains the burrow which is home to all three, constantly removing sand and small rocks which fall into the entrance. In exchange for the housekeeping, the tiny fish protect the shrimp by serving as its eyes. Whenever danger approaches, the gobies retreat into the burrow. When the coast is clear, one or both gobies stands guard. The shrimp, keeping one if its long antennae in nearly constant contact with a goby, knows from the actions of the fish, when the coast is clear. When the gobies go in search of food, the shrimp stays hidden in the burrow, safe from danger.
Also found digging in the sand, near the reef, is the goatfish. This curious creature has a pair of long whiskers called barbels which are used to sift through the sandy substrate. The barbels are chemosensitive, meaning that they can detect prey by its chemical smell. The goatfish feeds on small invertebrates like worms and mollusks, which it finds living in the sand.
Frequently found pulsating silently above the reef are jellyfish. Although these animals are commonly known as jellyfish, they are not fish at all. They are actually Cnidarians, closely related to anemones and corals. Like all Cnidarians, they have powerful stinging cells called nematocysts which are used to capture prey. Some jellyfish are potent enough to injure or kill animals as large as humans! Unlike real fish, jellyfish are weak swimmers, and are at the whim of the currents. They have little say in their direction, but instead follow the ocean flow.
Here's an animal with a cast-iron stomach. This sea turtle is a marine reptile, and eats things which few other creatures can digest. Among its favorite foods are poisonous jellyfish, and nearly indigestible sponges. The sea turtle has developed these remarkable eating habits to fill a space in the food chain, surviving on things which are not eaten by many other creatures, and therefore reducing competition for food. Although they breathe air and must hold their breath while submerged, sea turtles still sleep underwater, hidden from view, in caves in the reef.
The tropical South Pacific 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. The sand near the reef also supports life. 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, it is our responsibility to preserve and protect this delicate ecosystem thriving Beneath the South Pacific.