Welcome to Marine Mondays. 🐋🐠 Following on in the steps of Fossil Friday and Wildlife Wednesday is Marine Monday, where I’ll share marine related finds from along our beautiful coastline. Hidden mainly from view, below the surface of the sea, in the rock pools, under the waves, there is much “going on” underneath.
Today’s post features the Maori Octopus (Octopus maorum) of the Cephalopod class.
(I had promised myself to make posts shorter although this one is longer again. The next one will be far shorter so is more reader-friendly.)
This group of marine molluscs includes squid, octopus, cuttlefish and nautilus. Cephalopod translates to “head feet” and is a reference to the way the cephalopod’s head connects to its many arms.
The basic cephalopod body plan includes two eyes, a mantle, a funnel (also called a siphon), and eight arms. They have bilateral body symmetry, a prominent head, and their foot has been modified into arms or tentacles.
Cephalopods are found in all of the world’s oceans. They are found at all depths, from hydrothermal vents to the sea surface. All Cephalopods are carnivores.
Coloration of this species can vary and they will be either orange-brown or dark purple-grey. The Maori Octopus is a carnivore and is nocturnal (is active at night). It is the largest octopus in our area and whilst they only live a short life (around 2-3 years) they can reportedly weigh up to 12 kg when fully grown. The octopus has numerous small iridescent white spots on the web, arms and dorsal arm crown but there are no spots present on the mantle.
Octopuses are considered to be the most intelligent of all invertebrates . They have a highly complex nervous system, only part of which is located in its brain. Apparently about two-thirds of octopus’ brain cells are in each of octopus’ arms. Laboratory experiments with mazes and problem-solving have shown that they do have both short-term and long-term memory. The octopus also uses tools in it’s habitat and their arms show a wide range of complicated reflex actions. Some of my favourite stories involve anecdotes of the intelligence and problem solving skills of octopus.
Not only being intelligent and active hunters, their biology is also interesting.
Cephalopods are the only mollusks with a closed circulatory system. They have three hearts: two gill hearts that transport blood through the capillaries of the gills (to pack the blood with oxygen before transferring it to the large one) and a third larger single heart that pumps the oxygenated blood through the rest of the body. Cephalopods use the pigment hemocyanin, a copper-containing protein, rather than hemoglobin to transport oxygen. This means their blood is colourless when deoxygenated and turns blue when exposed to air.
They have suckers on their arms that are also extremely sensitive; they can pick up subtle chemical signals and move individually, even folding in half in a pinching gesture.
Octopuses are the “masters of disguise”. As well as having the ability to hide in very small spaces, as the only hard part of their body is their beak (much like a parrots beak), they can change their colour by the chromatophores in their skin, papillae, in just three-tenths of a second.
An example of the chromatophores in use is captured in the photos above (taken from a distance). It’s arms were active whilst it’s arms sought out crabs in the distance.
They also can raise their skin, up to 3cm in adults, to create a texture to match it’s surroundings (to mimic speficic objects, for e.g., to match a rock with bumps on it) so as to disappear into the underwater scenery) taking this level of camouflaging to the next level. Other defence and survival mechanisms include jet propulsion (from it’s mantle) for fast movements/escapes over short distances and activating it’s ink sac to create a “smoke screen” to distract it’s predator and allow it to escape.
Octopuses have excellent eyesight and a very well developed sense of touch. Octopuses move about slowly by crawling, walking on their arms, or by swimming.
All Cephalopods have a two-part beak and most have a radula, They feed by capturing prey with their arms, drawing it in to their mouth where they have a strong beak (much like a parrots) that breaks through the carapaces of crabs, and they take bites of their prey that includes, small fish, molluscs and crustaceans. To prevent their prey from escaping, they have modified salivary glands that produce a venom (a saliva with bacteria) although all octopuses produce venom only the small blue-ringed octopuses are deadly to humans. It is thought that perhaps these “juices” that are ejected from their salivary glands onto their captured prey also assists with separating the flesh of their prey from the bone or shell.
The Maori Octopus lives in the benthic zone (ocean floor), in soft-sediment and rubble habitats, with depths of 0-549m and will sometimes forage in nearby hard-reef habitats. I have spotted them myself in the intertidal zone in Aireys Inlet and Lorne. Whilst it is said that live in temporary shelters there are a few locations that are known as regular habitats. The one featured in this post was at Aireys Inlet, in the Eagle Rock Marine Sanctuary, and was sheltered under a semi cave, and was taking advantage of the overcast day to venture out to look for food during the late afternoon. I have also been gently tapped on the foot by a gentle inquisitive octopus arm whilst standing in a deep rock pool area for a lengthy time on a dark and overcast day.
They live solitarily in a den for up to 3 months at a time. They gather prey remains to form a midden (piles of shells, bones and rocks) which is used to conceal the entrance to their den.
The adult male and adult female octopus mate with the male octopus then becoming senescent and dieting shortly after. The female usually stops eating for 2 weeks during the laying eggs period and continue to look after the eggs until they hatched (a month). She may lay approximate 7000 eggs. Their eggs are usually clusters of 3-12 eggs and cemented directly to a rocky surface. The mother uses her arms to “sweep” across the eggs to keep them well oxygenated, clean and safe from predators. “During brooding period female will stop feeding so that it produce less wastes and ensure the water quality is good for the eggs. When the eggs are about to hatch the mother will frequently squirt water on the eggs using siphon until the eggs hatched.” After the eggs hatch, the female will swim away and dies shortly after, as she has been greatly weakened from her dedication in safe guarding her eggs. Newly hatched octopuses live amongst the plankton and eat copepods and larval crabs and starfish.
The main predators of adult octopuses are seals, eels, dolphins, sharks, sea lions, wobbegongs, school and gummy sharks, mulloway, queen snapper and dolphins, and perhaps penguins, as well as humans.
Cephalopods have existed since Carboniferous period, which is roughly 296 million years ago.
Happy octopus day to you.
– Rebecca Hosking