Biology of the Octopus Briareus (Caribbean Reef Octopus) -- Final Draft
This topic submitted by Lindsey Duff at 7:39 AM on 5/16/09.
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Biology of the Octopus Briareus: The Caribbean Reef Octopus
Octopus briareus, more commonly known as the Caribbean Reef Octopus, is one of the many species that form the class Cephalopoda. These mollusks are more than just bright colored coral marine animals that are an interesting site for divers; these creatures are one of, if not, the most intelligent and perceptive of all invertebrate. In addition to their intricate body structures, the Caribbean Reef Octopus uses its exceptional senses to survive amongst the perilous beings living amidst the ocean floor.
One of the most interesting characteristics of the Reef Octopus is the physical make-up of their boneless body. The octopus belongs to the phylum mollusca, meaning it is a creature with a soft, unsegmented body and lives in an aquatic or damp habitat. Octopus briareus species range in size from 40 cm to 60 cm, although they are able to grow to 100 cm at most. At heaviest, octopus briareus can reach up to 1.5 kg or 3.3 lbs. The octopus is then separated from the mollusks into the class Cephalopoda. Not only does this class include the most advanced animals of the phylum, the octopus has evolved most of the cephalopods since the class began over six hundred million years ago. The octopus differs from the rest of the cephalopods in that they have no form of inner or outer shell like the others. The term cephalopod, meaning Òhead-footedÓ, describes the octopus by referring to the fact that the animals in itsÕ class have arms that branch directly from their heads. The eight arms, used for almost every action the octopus performs, are attached to the head classifying the octopus as a cephalopod. More in depth of the octopusÕs anatomy, the mantle sits directly behind the head, opposite itsÕ arms. The purpose of the exceedingly muscled mantle is to house all of the organs of the animal. Crammed into this structure and protected by the strong muscles are the octopusÕs gills, hearts, digestive system, and reproductive glands. These powerful muscles in the mantle also aid with respiration and contraction. The gills located inside the mantle, sometimes referred to as the head, extract oxygen from the water. Once the water is passed through the gills, it is released by way of the siphon, or funnel. Of the octopusÕs three hearts, two of them pump the copper-based blood through each of the two gills. The last of the three hearts pumps blood through itsÕ body. The blood of an octopus is seen as the color blue because of the copper-rich protein hemocyanin that it contains. The hemocyanin dissolves in the plasma versus being inside the red blood cells, like human blood, giving the blood a blue color. The hemocyanin protein is used to transport oxygen. In comparison to human blood, which contains iron-abundant hemoglobin, hemocyanin is more efficient in oxygen transportation under cold conditions with low oxygen pressure. However, under normal conditions, the iron-rich hemoglobin of vertebrates is more efficient. Because the copper-based blood is sometimes not as efficient in oxygen transportation as our iron-abundant red blood, an octopus moving quickly or trying to escape runs out of energy and tires easily.
In the event of a fleeing octopus tiring, the cephalopod must defend itself incase a predator approaches. Although the octopus has no inner or outer protective shell, the creature has developed many remarkable defense mechanisms, which compensate for its lack of bodily protection. ItsÕ primary goal is to hide. The creature either does not want to be seen at all by its predators, or at least not to be recognized as an octopus. The octopus is often called the Òchameleon of the sea,Ó however; the octopus is able to change color much faster than a chameleon on land. In addition to its ability to camouflage, the octopus has astonishing agility, an extremely flexible body, and incredible intelligence. An octopusÕs classic defense, and the one most depicted in movies, is its use of expelling ink. Using this mechanism, the octopus squirts a cloud of ink, its body turns white, and then jet propels itself to safety. Once the mollusk is positioned in a safe location such as positioned against a rock or wall, it camouflages itself by changing its color and skin texture to blend in with its background. Its flexible boneless body allows it to squeeze into small caves or crevices for safety as well. When a predator or enemy attacks, the octopus will then uses its ink defense strategy. It squirts thick blackish ink in a cloud, which lingers in the water where it was ejected for several seconds. This allows just enough time for the octopus to escape and perform itsÕ color change. The main colouring agent of the ink is melanin. This chemical is the same chemical that gives humans their hair and skin tone color. The expelled ink cloud not only distracts the predator from the sight of the escaping prey, but the scent as well. The melanin in the ink cloud is thought to dull the smell of the octopus. This strategy is particularly helpful for fleeing from predators who are dependent on smell to hunt such as sharks. These life saving inkblots sometimes serve as pseudomorphs, decoys that the predator attacks instead of the prey.
Like the inkblot, an octopusÕ lost arm serves as a distraction. This strategy is known as an arm autotomy. If a predator, which for octopus briareus is usually a shark or stingray, attacks an octopus the sight looks like a blur because of the vigorous fight. During the fight, the octopus may lose an arm to the sharkÕs snapping jaws. Once its arm is detached and the shark focuses on the still-wriggling arm, the injured octopus turns white and darts away to safety. The lost limb distracting the predator will soon grow back.
If a predator approaches quickly and the octopus canÕt escape, its camouflage defense strategy may protect it. Depending on the background or environment, its skin changes texture to smooth or pebbly. In addition to texture, its skin transforms to the color of its hiding place. Although an octopus is color-blind, it still has a startling color sense. Specialized skin cells called chromatophores aid in the octopusÕ camouflage. Chromatophores are able to lighten or darken the skin to create a range of shades and patterns to mimic its background. These tiny sacs of pigment contract into small dots making the octopus appear lighter, whereas, if the octopus needed to appear darker the color cells would expand. These advanced skin cells can alter the apparent color, opacity, and reflectiveness of the epidermis. An octopusÕ color changing ability may also be used to communicate with or warn other octopi. For example, a color change may reveal the octopusÕ mood. A startled or scared octopus may turn white, while an angry or excited octopus may turn a deep red.
Another wonder of the complex creature is how an octopus moves about the ocean. While locomotion is familiar to humans using a pair of legs, the octopus moves about in an extremely different way. When hunting, it glides phantomlike across the ocean floor. The octopus extends its lead arms and bringing up its rear arms, thus pulling itself forward. Its fastest means of locomotion are by jet propulsion. Water is taken into the mantle through an opening near the front of the octopusÕ protuberant body. In order to move, the water is forced out through the funnel with a strong contraction of its muscles. Like a balloon releasing its air, the propulsion of the water shoots the octopus backward. The ways by which an octopus moves are intricate and fascinating.
In addition to a complex body structure, the octopusÕs eye is quite intricate itself. The pupil differs from the human pupil in that rather than a round dot; the pupil is a horizontal stripe. Similar to the human eye, both have comparable structures: retinas, crystalline lenses, irises, eyelids, and pupils. Researchers have found that even though octopus cannot detect color, their capability to perceive texture and tone is more than compensating. In addition to its keen sense of sight, the octopus can turn its eyes 180¡, allowing it to look behind itself without actually turning its body around.
Not only does the physical body make-up of the octopus set it apart from the other spineless creatures, their devotion to their young is like no other. Octopi take parenthood very seriously, literally to the point of death. The reproduction period usually lasts one to two months and tends to be during the month of January. Scientists have researched and observed that size matters in the event of mating. One scientist noted that, ÒA large male will stand just outside a femaleÕs den, and a smaller male will wait five to six feet away, and still smaller males another six-foot distance away.Ó During the reproduction process, the male passes sperm packets called spermatophores down a groove in its third right arm. The male then ÒmountsÓ the female and inserts the hectocotylus, a unique spoon-shaped tip, into her mantle. The hectocotylus carries the spermatophores into the femaleÕs oviduct. Mating for the Caribbean Reef Octopus usually last for approximately half an hour. Also, octopus briareus usually mates during the day and mating can only be initiated and stopped by the male. After the spermatophores are transferred the female returns to her cave. For protection, she may seal off the entrance to her den by building a wall of stones. Once inside her lair, the mother octopus attaches strings of eggs to the ceiling. After being fertilized, a female of octopus briareus can store sperm in its oviduct for up to 100 days. It can then lie up to 500 large eggs. The soon-to-be-mother then rests with her eggs until they are ready to hatch. The laid eggs take between 50 to 80 days to hatch, depending on the temperature of the water; eggs hatch quicker in warmer waters. At birth, baby octopuses are able to jet propel themselves around and expel ink. In just 150 days after birth, both male and female babies reach sexual maturity.
The statement that octopuses take birth so seriously, even to the point of death, is not a figurative statement. The life span of octopus briareus ranges from ten to seventeen months. Some octopi undergo a 2 to 4 week deterioration period just before natural death. During this time, feeding is scarce and sporadic. For males, this deterioration period occurs shortly after mating. For females, death mainly occurs quickly after egg laying. During reproduction, the female starves itself and doesnÕt eat for a long period of time. Even if a predator approaches her eggs, the mother octopus may attack and possibly kill the enemy but will not eat it. While protecting her eggs, the mother will not leave the den to hunt and will even refuse food that is brought to her. Throughout the duration of egg hatching, a female may lose more than half of her body weight and may eventually die of starvation, if not some other cause sooner.
While they donÕt eat during reproduction, octopuses do have an intriguing way of hunting when they do feed. Back to the complex body of the octopi, the eight arms do more than just help the creature move about the ocean. Covering each arm in double rows lie approximately 240 highly sensitive suction cups. In total, an octopus may have nearly 2,000 suckers on its arms. These suction cups, or suckers as their sometimes referred to, are made of strong sets of muscles that allow it to contract, stretch, or bend at any given time. By lowering the pressure inside the sucker, a vacuum seal is created allowing the sucker to grip an object. These objects can range from a pebble or rock, to its prey or even a human hand. The suckers are so strong that they can be folded over objects as small as fishing line or a pebble. For octopus briareus, hunting usually consists of lying and waiting in its lair, but if enough time passes and no prey is seen, the predator will venture away from its den to find food. In the hunting process, these suckers come into use when the octopus pokes its arms into cracks and crevices. Not only do the suction cups seize prey, but they can taste as well. Chemoreceptors, the rim of the sucker that is loaded with sensory organs, are so highly sensitive in their taste and smell senses that they can even distinguish a live clam from a dead one. Similar to a snake, the skin of the suckers is shed routinely to keep them aware and agile. When prey is spotted, such as a crab on the ocean floor, the octopus swoops down opening its webbed arms to create a canopy to net its target. The Caribbean Reef Octopus mainly targets crab, shrimp, lobster, polychaetes, and a variety of other fish. Crabs seem to be preferred because shrimp and other prey are often too fast and difficult to catch. After planning its kill, the octopus the closes around its prey like an umbrella and totes the crab back to its den inside a sac of water. To tranquilize an aggressive crab or other prey, the octopus secretes a chemical into the pouch. Once safely inside its lair, octopus briareus crack open the shell using its suckers or beak, much like that of a parrot, which is hidden inside its mouth at the center of its arms. Its poisonous bite paralyzes or kills its prey so it can eat in peace. Depending on the conditions an octopus will eat more of less often. As stated before, females do not feed at all during the period of reproduction. Studies have shown that in warmer waters and where food availability is greater, food intake increases. An experiment conducted in California showed that food intake doubled with a temperature rise of 10 degrees Celsius and the doubling of crab density. It was also found that overeating had no effect on food intake. However, a female will cut down her food intake by 50% a few weeks before she lays her eggs. Food consumption is affected by water temperature, crab or prey density, and food deprivation. Most octopuses are not directly given food; consequently, they must hunt. Not all species hunt only at night; octopus briareus are nocturnal and have been observed to catch their prey at dusk or dawn. An octopus greatly depends on its extraordinary senses of smell and vision to hunt.
Supplementing the cephalopodÕs exceptional senses of smell and vision is its astonishing intelligence. Octopus briareus is one of the, if not, the most intelligent of all invertebrate. Although this may seem surprising, it makes the most sense considering the size of its brain compared to its overall body. The creature is basically a head with arms; therefore, its brain seems colossal for its size. Many laboratory experiments have been conducted to gauge just how intelligent these creatures are. The octopus has the ability to retain the knowledge of what technique another octopus of the same species uses to accomplish a task. The phrase ÒMonkey see, monkey doÓ seems to be applicable to the octopus species as well. Some experiments have witnessed the species disguising themselves as algae or coconuts in order to avoid predatory detection. Because their mothers die so shortly after their birth, baby octopuses cannot learn from their mothers like so many other animals do. This may be why octopi have developed such a strong intelligence so they can survive on their own.
These brainy creatures inhabit in solitary places; consequently, octopus briareus are hard to spot. The easiest time to spot these octopi is at night while they are feeding on reefs and seagrass beds. Using a dive light helps to detect the creatures because their blue-green skin is so reflective. Other than that, the nature of the Caribbean Reef Octopus is known to be shy and hermitic. Only during mating will one interact with another. Octopus briareus remain safe and avoid instigating fights if they stay at least 60 feet from one another. These creatures mainly reside in secluded, rocky dens that are difficult to locate. These shelters are usually created or found in shallow warm waters. While they remain anchored in one habitat during egg hatching, octopi spend the rest of their lives moving from one home to another. Because they inhabit in warm shallow waters, the Caribbean Reef Octopus is commonly found throughout the Florida Keys specifically, Western Atlantic, Bahamas, Caribbean, and coasts of northern South America.
Since they live in such shallow warm waters which are, most of the time, waters that tourists vacation to, one may wonder the relationship these creatures possess with humans. Although movies often depict octopus as Òmonsters of the sea,Ó octopus hold no real danger toward humans. If a diver pokes his finger into an octopusÕ habitat, he may feel several arms suction his finger and prevent him from pulling it out. If the diver doesnÕt panic, the octopus will soon tire and release its grip with no harm done. The only species of octopus that are truly dangerous to humans is one of the smallest, the blue-ringed octopus. Its venomous bite can render a human dead in just a few minutes. As for octopus briareus, it can only bite or suck, but does not possess venom strong enough to kill a human. The Common Reef Octopus has no positive or negative economic importance to the human race. It is not sought after for any particular characteristic and is therefore, not in any danger of extinction thus far due to humans. In addition, the octopus briareus has no specific predator that poses a threat to its existence.
The Common Reef Octopus is a complex and interesting creature that is overlooked by many curious divers. This cephalopod is one of the most intriguing underwater species that exists. From its intricate body structure to its astonishing intelligence, the octopus possesses a puzzling existence that can and will be studied for years to come. Laboratory research of octopus briareus is also easily available because the species can be bred almost effortlessly. Because of their ability to multiply easily, scientists can continue to gain further knowledge of them. Even though a great deal of information is already known, there will always be more to study and discover.
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