Octopus spotting in the TCI.

By Dr. Caitlin E. O’Brien, The School for Field Studies Center for Marine Resource Studies

Octopuses are among the most intelligent of animals without a backbone.

Caribbean waters are home to several species of octopus, which are some of the most extraordinary creatures of the ocean. Octopuses (not octopi) can be more difficult to spot than many other marine creatures, but the experience of seeing one is well worth the effort.

What are they?

Octopuses are Molluscs in the Class Cephalopoda, along with squid, cuttlefish and nautilus. The word “cephalopod” originates from the Greek words for “head” and “foot,” referring to the fact that their heads are attached directly to their “feet.” Cephalopods first appeared around 500 million years ago as shelled creatures known as ammonites, nautiluses and belemnites. Ammonites later went extinct, existing today only as spiral fossils popular with collectors. Most nautilus died out too, although six species still exist in the Indo-Pacific Ocean. Belemnites eventually evolved into the 800 or so species of squid, cuttlefish and octopus known today. Among these, most of the approximately 300 species of octopus live in shallow, coastal areas, although a few deep-sea and pelagic species are also known.

Octopus biology is quite bizarre. In addition to a soft body with eight arms (not tentacles), they possess three hearts and have blue blood due to the presence of copper (hemocyanin) rather than iron (hemoglobin). The arms are also quite extraordinary. Covered with hundreds of flexible suckers, they are capable of adhering to almost any surface with considerable force. Not only do they assist octopus in locomotion, but the suckers also have the ability to “taste” in order to help locate tasty critters under rocks and corals. Equally extraordinary is the fact that an arm severed from the body will eventually grow back, and sometimes an octopus will even intentionally sacrifice one to a predator in order to escape.

A common corpus swims across the sea floor.

Octopus have a wide range of near-supernatural tricks to protect themselves. They can avoid being seen in the first place due to their ability to change the color, iridescence and texture of their skin. Small sacs of ink expand and contract to instantly create different colors and patterns, and to modify the skin’s reflectiveness. The effect is accentuated by muscles that can raise or smooth out patches of skin (papillae) to create a rough texture resembling algae. When threatened, octopuses can escape by squeezing themselves through any hole larger than their parrot-like beak. Alternatively, they can propel themselves rapidly away by quickly sucking in water and shooting it out their siphon. They may also eject ink at the same time, either in the form of a gelatinous blob to act as a diversion or as a “smokescreen” to hide behind. Predators of octopus include sharks, dolphins, eels, large fish and humans.

Octopuses are largely asocial creatures, only seeking out other octopus towards the end of their lifespans in order to mate. Before then, they try to steer clear of others in order to avoid being eaten by one of their own. Octopuses have only one reproductive event in their lives, although both females and males can mate multiple times. After reaching the end of their natural lifespan (usually one to two years), males will go through a period called senescence, in which their bodies rapidly deteriorate and they behave recklessly, often swimming in the open without regard to predators before dying or being eaten. Females on the other hand will select a well-protected crevice in which to lay their eggs. Thereafter, she will carefully tend to them, fending off predators and gently cleaning their surfaces of debris. During this time, she forgoes food and rarely leaves the den. When the eggs hatch several weeks later, she dies and the planktonic young go on to drift in the current until they are large enough to settle on the seafloor.

Octopuses are among the most intelligent of animals without a backbone (invertebrate). They can solve puzzles and mazes, and are notorious for their Houdini-esque feats of escape from aquarium enclosures. This cognition is made possible by one of the largest of invertebrate brains, consisting of more than 200 million neurons, and which is donut-shaped and wrapped around the esophagus. In addition, each of the eight arms has its own “mini-brain” which allows it to perform actions semi-autonomously. In fact, an arm that is severed from an octopus will still move, seemingly unaware that it has been disconnected.

How can I find them?

A Caribbean reef octopus envelops a coral head with its arms in search of prey.

Octopus of the Caribbean are typically found in relatively shallow (<10m) waters sheltering in natural rock or coral crevices, within small holes in the sand or inside seashells or human trash. When approached by a diver or snorkeller, an octopus may retreat deeper into their den or attempt to escape. If this happens, the best thing to do is be as still as possible in order to allow the octopus to habituate to your presence. However, some octopus are extremely curious and may reach out to touch you. If this happens, there is nothing to fear: as soon as they realize you’re not a crab they will likely let go. Less often, octopus can be found out hunting. In this case, it is best to sit back and watch . . . no one likes being interrupted during dinner!

Octopus vulgaris, the common octopus

In addition to the Caribbean, this species can be found in tropical and temperate waters across the globe. It ranges in color from solid white to brown, along with a variety of mottled patterns. The common octopus can grow up to three feet long from mantle to arm tips, and hunts crustaceans and bivalves in rocky areas and coral reefs. It is a crepuscular species, meaning it prefers to hunt at dawn and dusk, although it may be found out and about at other times as well. However, the best way to find one is to look for holes and crevices with a shell “midden”— piles of shells and rocks around the den entrance representing prior meals as well as providing octopus with a sort of “shield” if a predator attacks.

Octopus briareus, the Caribbean reef octopus

The Caribbean reef octopus is one of the most beautiful octopus species due to its typically rainbow appearance. While they are predominantly blue, they can take on a range of colors and mottles, including dark red. Fully grown members of this species can weigh up to three pounds, eating crustaceans hidden in crevices of coral reefs. This species is nocturnal, spending daytime in difficult-to-locate dens. For this reason, the best way to see one is to go night diving or snorkelling on a shallow coral reef.

Macrotritopus defilippi, the Atlantic longarm octopus

The Atlantic longarm octopus is the smallest of the three species, with the body growing up to three and a half inches. However, as its name implies, its arms are very long and it can sometimes be seen using these arms to masquerade as a flounder. Its color can be anything between solid white to mottled yellow and brown. It hunts small crustaceans on the sandy sea bottom and in seagrass beds, and unlike the previous two species, can often be seen doing so during the day. Dens are more difficult to locate, as this species has the ability to bury itself completely in sand.

Now that you know a little more about these amazing creatures, you’re ready to get out in the sea and go octopus spotting. Good luck!

Further reading

Hanlon, R.T. and Messenger, J.B., 2018. Cephalopod behaviour. Cambridge University Press.

Jereb, P., Roper, C., Norman, M., Finn, J., et al., 2016. Cephalopods of the World. An Annotated and Illustrated Catalogue of Species Known to Date. Vol. 3. Octopods and Vampire Squids.

Humann, P., Deloach, N. and Wilk, L., 2002. Reef creature identification: Florida, Caribbean, Bahamas.