We are all familiar with the terrifying story of Captain Nemo’s submarine which sailed into the depths of the ocean and was suddenly captured by a monstrous octopus which threatened to sink it. The resourcefulness of the captain prevented the terrible tragedy. People often wonder if the account of the giant octopus which can encircle a submarine and threaten to sink it, is a true story or just a great fairy tale for children.
Evasion under an ink cloud
Octopuses are the cleverest and most interesting of all the marine creatures. They belong to the mollusk family which includes animals without a supporting internal skeleton such as the snail. But unlike the snail, which is supported by an outer shell, octopuses have neither a skeleton nor a surrounding shell. Every octopus has eight tentacles which it uses to move along the sea bed and over the rocks of the reef. Each tentacle is covered by tens of suction cusps each of which has strong adhesive power.
There are a number of ways the octopus can defend itself against danger, the primary one being the ejection of an ink cloud, emitted from a sac full of black ink located in its body. In times of danger the octopus squirts ink into the water and escapes under cover of the resultant thick, dense and murky cloud. The octopus can eject a number of ink clouds before the ink sac is completely emptied. Apart from the ink, using special pigment cells found in its skin, the octopus can camouflage itself perfectly well by rapidly changing its color to that of its surroundings. In addition, by creating protrusions and changing the texture of its skin, the octopus can change its shape and size, remaining so well camouflaged that one can pass by and not even notice it.
With the help of its sharp eyesight, the octopus can identify a predator from a great distance before being identified. At that instant it freezes on the spot, its color blends into the surroundings and its eyes contract until the danger passes. When in danger, octopuses excel at rapid swimming but only for very short distances. They do this by creating a forceful burst of water which propels it forward, a movement reminiscent of a jet engine.
Together and Separate
Octopuses are not particularly social animals and every octopus has a habitat which it guards jealously even from its own species. However, despite being solitary animals, every year one can see pairs of octopuses spending a few hours together. This occurs in the mating season – spring, during which the male octopuses begin to move along the length of the stony sea bed in search of a female. Upon meeting another octopus they carefully examine each other from a distance, checking out the other’s size, and the males confirm that it is indeed a female opposite him and not another male. After the examination ritual and the establishment of a suitably sized couple, the two of them settle on a stone. The male extends his breeding tentacle embellished with a small number of attachment cusps, and from his mantle (body cavity) removes a sac containing sperm, which he passes into the mantle cavity of the female. The reproduction process takes a few hours and while it takes place the two octopuses sit quietly, glassy eyed, and oblivious to their surroundings. Large grouper fish exploit these opportunities and more than once can be observed trapping an octopus during the reproduction process. After passing the sperm sac to the female, the couple hastens to separate before one of them develops an appetite.
After fertilization, the female octopus begins to look for a suitable rock den. Once found, she enters the aperture and over a few days seals the entrance with coral fragments and shells. All attempts to open the den of the female octopus are met with stubborn resistance and no fish is able to penetrate.
The female lays a large number of eggs, up to a thousand per batch, then protects and ventilates them in fresh water to prevent bacterial and fungal infection. The safeguarding period of the eggs lasts about 50 days, during which the eggs develop and hatch under the watchful eye of the mother. At the end of this period, when the young octopuses leave the den, the life cycle of the female is usually over and she dies. The tremendous amount of energy expended in building the nest, laying the eggs and guarding the young octopuses at the start of their lives, saps the energy of the female, who does not feed during this period. In most cases, female octopuses do not manage to survive after the end of the reproduction season, whereas the males survive two and even three reproduction seasons. Only one or two of the hatched octopuses will survive till maturity, the majority being eaten by fish and crustaceans in the first stages of their lives.
Sophisticated Hunting Mechanism.
The diet of the octopus is mainly comprised of fish and crustaceans with the hunt usually taking place in the early hours of the morning or when the sun is about to set. The octopus has a highly developed sense of sight and can see sharply and clearly over a long distance. Octopuses like settling on a branching stony coral which it envelops with its tentacles. From time to time, by extending a tentacle into the branches of the coral and utilizing its suction cusps, the octopus traps one of the frightened coral fish. Usually it does not hunt like this alone, and is joined by a large grouper fish and an adult lionfish. These fish swim alongside the coral and catch any poor fish which, having managed to evade the octopus’s tentacles, is trying to find shelter in another coral. On the other hand, they also help the octopus in its hunt because upon seeing them, the coral fish hesitate to leave the coral branches. In this way, with its suction tentacles, the octopus manages to catch the fish and bring it into its sharp, strong parrot-like beaked mouth. The octopus rarely sees its prey. Its eyes, situated high above its head, scrutinize the surroundings spying out predators, whereas the tentacles are busy searching for food.
There are many different species of octopuses in the world: the largest reach a length of up to seven meters, and the smallest octopus at maturity is no longer than a centimeter. In Australia there is a small species which lives in shallow water, and which in addition to its camouflage ability, has a very potent poison. When the octopus is held, it simultaneously bites and injects its poison which can kill even an adult. In order to warn predators and keep them away, the octopus is covered in bright blue circles acting as warning colors. But by bad luck this color attracts the eyes of small children, and more than once children have been injured by the poisonous bite.
So are there really giant octopuses of the size described by Jules Verne? As far as we know such enormous octopuses do not exist, though there is a species of giant squid, the colossal squid, (a relative of the octopus family), whose tentacle length can reach up to 20 meters! It is known that whales, who feed on deep sea squid, rise not infrequently to the surface of the sea with signs of a struggle in the depths of the ocean covering their body.
So maybe the story of giant octopuses is only a legend, but octopuses are without doubt one of the most interesting creatures living in the sea.
The Underwater Observatory Octopus
At the Underwater Observatory in Eilat one can learn about the high intelligence of octopuses and their learning ability. There, one of the aquariums is dedicated to the adult octopus. In consideration of the solitude which he likes, the aquarium is for him alone. Because the octopus is by nature a curious animal and enjoys stimulation and cognitive assignments, the underwater observatory challenges him with different activities. The food of the octopus is offered to him in a closed bottle with a screw lid. In order to get the desired food, the octopus must open the lid, put his tentacle inside and draw out the food. Octopus feeding takes place daily at 11.30.
So are there really giant octopuses of the size described by Jules Verne? As far as we know such enormous octopuses do not exist, though there is a species of giant squid, the colossal squid, (a relative of the octopus family), whose tentacle length can reach up to 20 meters!
There are a number of ways the octopus can defend itself against danger, the primary one being the ejection of an ink cloud, emitted from a sac full of black ink located in its body. In times of danger the octopus squirts ink into the water and escapes under cover of the resultant thick, murky cloud.