Transcript
The Ocean Dancers Cephalopods ignite imaginations. Evoking images of seafaring monsters and alien life forms. More positively their imagery has provided great design ideas that have decorated our homes, bodies and our plates. But these fascinating creatures are so much more than that.
Of the higher classification Mollusca, cephalopod means “head-foot” in Latin. The comical name does not add to its reputation of being an advanced invertebrate. There has been minimal change in there form from the over 200 million year old fossils that have been found. This makes their lineage older than dinosaurs. Of the 800 species that are known 300 are octopus and are the most researched of the four subspecies which means much more information can be elicited about them. This is compared to the other species of cephalopods being squid cuttlefish and nautilus.
In brief, an octopus has 8 arms and three hearts. Two of which move blood beyond the gills whilst the third ensures the blue blood flows to the organs. The colour comes from the copper based haemocyanin which is more effective at transporting oxygen in the colder and more hypoxic environments of the deep ocean. All of its vital organs are located within its head however 65% of its 500 million neurons extend through to their arms. Therefore their arms can
move independently from each other. This allows the octopus to multitask without involving its brain in most of its activity. Additionally each sucker can move independently of each other. With a large sucker being able to hold up to 16 kg and with an average of 240 suckers or cups per arm these versatile arms are also very strong. Each of the 400 plus species of cuttlefish and squid has 10 arms. Two of which, their tentacles, are specialised for feeding. Some deem it hard to distinguish between the two subspecies and reading such statements as “every squid can be called a cuttlefish but not every cuttlefish a squid” does not ease any confusion. Anatomically squid are more slender with their eyes located more towards the side of their head. Also a few species of cuttlefish can be seen with an external shell. This is a common characteristic of a nautilus. So too, are their 90 tentacles. When aiming to distinguish between species of cephalopods confusion can easily befall most when looking at some of their names. Take for example the vampire squid which is actually an abyssal octopus. The striped pyjama squid is a species of cuttlefish and the dana octopus squid is a squid that looks like an octopus! Cephalopods are found throughout the world’s oceans. From the shallow waters through to deep open, pelagic, waters. As technology enables further exploration of the depths the vastness of their habitats continue to amaze. Last year hailed the find of the Stubby Squid, a purple toy-like creature which was found at 900 metres depth. Another recent find was Casper, found on a 4000 km deep survey of the Pacific floor in Hawaii. The deepest point at which any cephalopod has been seen to date was a Dumbo Octopus down at 7000 metres depth. As is evident there is a more gelatinous transparency to the deep water species compared to its more muscular shallow water cousins. Mainly due to the inadequacy of food at depth and it takes much energy to build muscles.
Birth and Death. The lifespan of cephalopods is short. The average life of an octopus is 3-5 years whilst cuttlefish and squid are in the oceans for 1-2 years. The deep water species living longer than their shallow water cousins due to their slower metabolism. Within their lifetime the timelines, especially of octopus are significantly variable. Their period of sexual maturity will vary depending on external, environmental factors. For example the Dumbo Octopus will carry eggs at differing stages of maturity and will use the sperm she has collected only when the conditions are optimal.
Multiple males will provide sperm to the hen either via their specialised arm. Or as in the case of the male blanket octopus a detachable arm, a hectocotylus, is taken off and given to the female. As you will see later that is a powerful gift from something so small. The male dies shortly thereafter. Admittedly the female may hasten the process by strangling then eating them. The hen then tends for up to 40000 eggs from three months to one year during which time she eats nothing. The eggs are mostly kept stationary but some species do carry them around as seen with the blanket octopus. During the brooding process the eggs will be cleaned by bubbles being washed over them. Upon the birth of the baby octopus, which is the size of a flea, the hen dies from malnourishment. This leaves the juvenile to fend for themselves.
Size Cephalopods are mainly solitary creatures. Juveniles may school and squid may gather in schools during the day to then hunt individually at night. However you will never find different sizes of the same species together as they are well known for their cannibalism. Sizes between and within different species can vary significantly. Take the blanket octopus. Being around 6.5m the female is 40000 times bigger than the male which grows to no more than one inch. It is the most significant size discrepancy between genders in the animal kingdom.
Deep Water Gigantism can be seen when viewing the largest invertebrate on earth, the elusive Giant Squid. It can reach up to 18m in length and weigh 1600kg. Mostly found at 1000m it inhabits the waters around New Zealand. The NE-NW Pacific holds the biggest octopus as yet to be found. Each arm of the 10m long, 50kg body of the Giant Pacificus can be up to 2m. And of the cuttlefish the largest is the Australian Giant which can weigh up to 5kg.
At the other end of the significantly long size spectrum is the smallest of the species. The 1gm pigmy squid is about 10mm whilst the Octopus Wolfi, being 1 inch is the smallest octopus. Through all these facts the biggest surprise may be concerning the Vampire Squid. The image and its name portray an animal much more foreboding and larger than its actual size of 6-15 inches.
Mobility. The ability of jet propulsion makes cephalopods the fastest marine invertebrates, even out maneuvering most fish. This is especially true of squid and cuttlefish even though most movements for them are in reverse. Their streamlined nature enables them to reach speeds up to 25mph in short bursts. At which time they sometimes leave the water. Another physiological feature is the lack of any real form of a skeleton which enables a significant degree of flexibility. The spine line structure, a pen, of the squid and cuttlefish is their only form of skeleton. But the octopus is the real contortionist. With only having a small piece of cartilage around the area of its brain and its beak as restrictions they are able to fit into an area less than a third its size. This is something remarkable to see. Some species like the Glass Octopus, only ever touch the sea floor to mate. They expend little or no energy by allowing the currents to propel their neutrally buoyant bodies along. The Adorabilis Octopus shape is perfectly adapted for this with its webbed tentacles. Sensory receptors, statocysts, acknowledge the rules of gravity and ensures the octopus stays the right way up whilst floating. Crawling along the seabed is the preferred, energy conserving action of the shallow water octopus as one of their three hearts stop when they are swimming. It has been noted that other species never leave the sea floor. A good example being the Flamboyant Cuttlefish and The Coconut Octopus which walks or ambles along the sand.
Intelligence Teuthology, cephalopod research, started over 100 years ago and mainly centered on Octopus. Therefore it has long been understood that they have the most complex nervous system of all invertebrates and their study has significantly enhanced the understanding of the nervous system in general. Even though their brain is the size of a walnut the body to brain weight ration far exceeds that of other invertebrate’s fish and reptiles. Octopus can conceptually think thereby learning by themselves and from others. They have the ability to feel pain and have individual temperaments. Some have been observed playing. Taking things apart for fun. They can navigate through mazes, solve puzzles and display memory retention both cerebrally and within its numerous suckers. The first instance of tool use was observed with the coconut octopus transporting and using the shell of the coconut to hide from predation.
Eyesight Their eyesight is the most complex of the invertebrates. Vision is acute, however all octopus and most squid and cuttlefish are considered colour blind. They have only one visual pigment but an enhanced sensitivity to recognise differences in contrast and brightness. The Firefly Squid is thought to be able to distinguish between species according to the wavelengths of light they emit during bioluminescence. It will be expected that the biggest invertebrate will have the biggest eye, and admittedly the 25cm eyeball of the Giant Squid will serve its purpose in increasing the efficiency of sight in the light-less depths. However the cephalopod with the biggest eyes relative to its body is the Vampire Squid.
Diet Each of the numerous suction cups on the octopus arm has chemoreceptors so it tastes whatever it touches. The significant innervation of their arms allows for this sensory loading to be processed and helps the octopus be the deceptively veracious predators they are. Easily able to desiccate its meal with its beaklike jaw. Animals within their diet include crabs, prawns, others mollusc's and even other octopus of the same species. Species specific diets include Giant Octopus eating sharks and Blanket Octopus favouring turtles. The deeper species such as vampire squid rely on detritus, or ocean snow. Gathering up the remnants of dead plants and animals on their sticky tentacles. They are opportunists. Eating whenever food is available. Conversely the shallower living species tend to hunt during the night. Their territory not limited with some species travelling significant distances to find food. This movement is mainly from deep towards shallow as seen with the nautilus which will vertically travel around 100 metres per day to feed. One species of octopus has even been observed traversing across the land to hunt.
Most species of cephalopods are venomous. In octopus the venom is stored within the salivary glands and originates from bacteria. After the strong beak penetrates the animal the toxin paralyses then softens the flesh. The blue ringed octopus is in the top five of the world’s deadliest animals and is the only one harmful to humans. Found only in S. Australia and the Coral Triangle in the Indo-Pacific region. Being the size of a golf ball is not an immediate give away to its potency but its colour is. The neurotoxin, tetrodotoxin, is 1200 times more potent than cyanide and one bite can paralyse and kill humans in minutes. A 30gm octopus has enough venom in its saliva to kill 10 people. Let’s wonder whether the woman seen holding the octopus is aware of this fact. Other venomous cephalopods include the Flamboyant Cuttlefish with the toxin in its flesh, and the Striped Pyjama Squid which releases toxic mucous from glands under its body
Camouflage The creatures that predate upon cephalopods are numerous, including turtles, sharks and sperm whales which favour the Giant Squid. As most haven’t any form of external protection they have developed some fascinating means of defensive strategies which can also be tailored to meet offensive and communication needs. Octopus mostly, but some cuttlefish and squid display crypsis. The ability to blend in with their environment, through changes in colour, texture, shape and locomotion. Adding up to around 50 unique behaviours.
Bioluminescence is light produced by biological activity such as the chemical reaction of bacteria. This could emanate from their light emitting organs, the photophore's, which can be up to 5cm long as seen on the Dana Octopus Squid, or within its secretions. A prime example is the Vampire Squid. It can pulsate the photophore's, which cover most of its body, whilst producing bioluminescent mucous from the tips of its arms. If the predator is not sufficiently confused the vampire squid will bite off one of its legs. The dispatched glowing limb will hopefully lure the predator away. Squid are also known to amputate portions of their arms to distract prey or predator. Differing sequences of bioluminescent patterns have been noted as communication tools when observing the Humboldt Squid.
Firefly squids are good examples of a species that have photoreceptors, proteins, embedded in their skin. They have the ability to control the degree of bioluminescence illuminating form its underside so that it meets the brightness of the surface. Prey will then be unable to see them from below. A tactic called counter illumination. It is even theorised that they can achieve this without even involving their brain.
Some cephalopods can camouflage within 3/10 of a second by contracting muscles around the many chromatophores, colour cells, within their skin, thereby changing colour. There can be up to 200 chromatophores within the size of a pencil eraser so the skin of a squid can easily have 10 million cells. Another means to achieve colour change is by the reflective plates within skin. Iridophores, leucophores and reflector cells allow for the mirroring of metallic colours, white hues and blue-greens respectively. However, the more complex the environment the
more intricate the colour change. Therefore a significant difference can be seen between the benthic and pelagic species. In the open ocean some species have no chromatophores at all as seen with the ghostly Casper. If they do then any colouration is restricted to simple disruptive camouflaging. Making their body outline less easy to see. Some species are restricted to just one colour change as seen with the bright red colour of the Humboldt squid. The wavelength of such a colour is so short that it will become invisible. In shallow water species not only is there a complex intricacy of the camouflage, some cuttlefish can rhythmically pulsate their colour changes to mesmerise their predator or prey. Additionally they can use the dark hues of aggression on half their body in response to males whilst displaying the light colour of courtship to the female on its other side. .
No other cephalopod can display mimicry better than the aptly named Mimic Octopus. Creating illusions, by changing its posture, shape and behaviour to resemble a multitude of other animals. By extending two arms and burying the rest it will resemble a sea snake or by splaying all its arms to take on the appearance of a lionfish. It will even flatten itself out and move away from the seabed and swim like a fish. Mimicry, however, is not restricted to this species alone. Algae Octopus uses its arms to look like wispy strands of seaweed. Squid will position themselves upright and splay their arms to resemble plants. Papillae, small protuberances on their skin, ensure the cephalopod's textural appearance mirrors that of their background. Whether this be rock, sand or vegetation.
Some species can be seen to mimic animals much larger and offensive than themselves, by displaying diematic behaviour. In other words shock tactics. One characteristic that enables this is the use of ocelli, or false eyes. This deterrent is used by the Vampire Squid. Other will display highly visible colours and extend their arms to appear as large as possible. A good example being the Blanket Octopus which will unravel its webbing to increase its apparent size. If a further deterrent is needed they will detach the blanket serving to entangle the predator.
If all else fails some octopus will either bury themselves or simply hide behind the nearest object available.
When they cannot blend in with their environment they will aim to change it by expelling ink. Ink sacs have been found in fossils and is therefore a defensive strategy whose composition has needed little modification over millennia, Not only does the dark melanin cloud serve to disrupt the attackers vision the substance contains dopamine which is thought to dampen the predators sense of smell and taste. It has been noted that ink can be projected in the form of pseudo morphs or false bodies to act as a lure whilst the cephalopod escapes. Some squid, more specifically of the deeper seas, produce and expel bioluminescent secretions at the same time as inking. An extra defensive manoeuvre.
The expelling of the ink and propelling away is known as the Blanch Ink Jet tactic and followed by most cephalopods but not all. Usually the transparency of the Glass Octopus works to its benefit but last resort will involve it pulling its head into its body. Turning itself into a sphere armed with mantles of tiny teeth and then ink so it disappears into the darkness. Not all species have a functional ink sac such as the Vampire Squid so they rely more heavily on the other strategies mentioned.
The Coconut Octopus has already been mentioned for its use of the husks to hide in. However cephalopods are variable in their choices of tools to provide shelter. From glass bottles, cans to discarded shells. Shallow water octopus have often been seen laying claim to territory by decorating the area with anything they can find. But it is one octopus that stands out from the crowd when talking about tools. The Blanket Octopus, being immune to the sting of the Portuguese Man O War will rip off their tentacles and attach them to their own arms. These will then be used to attack the jellyfish themselves or other predators or prey.
This information has admittedly just skimmed the surface of the world of cephalopods. Here’s hoping the next time you see these creatures dancing around the ocean, like these local residents, then they will stoke the fires of fascination for you too!
