The Mimic Octopus

Foraging behavior

When the mimic octopus is not at rest, it is usually foraging. Norman’s study observed that mimic octopuses are mostly diurnal foragers (Norman, 2001.) A previous study conducted by Norman and Hochberg suggested that the mimic’s diurnal lifestyle and habitat may have evolved through one of two scenarios: a habitat shift by a day active ancestor, or from an activity pattern shift from a night-active (Norman, 2005.) These two scenarios give rise to different possibilities as to why a mimic octopus would be diurnal, which has caught scientists attention because the common octopus, as well as other octopus species, are nocturnal foragers. There has also been some unique foraging tactics presented by the mimic octopus that have not been seen in other octopuses. Several mimic octopuses were observed entering a tunnel completely an emerging from another hole up to 1 m from the area the entered through (Nabhitabhata, 2007.) This is very uncommon in octopus species because they usually will camouflage until their prey come around.

Moving Around

Regardless of its foraging techniques, the mimic octopus shifts into day foraging and movement by masking its presence visually from local predators through the impersonation of other dangerous local predators. Moving in a shallow, open environment is not an easy task for a boldly patterned octopus such as the mimic octopus; it can easily be noticed and pointed out by other predators. Therefore, one of the most interesting adaptations the mimic octopus has developed is its ability to mimic different predators who are co-living in their environment, which allows it to move without being attacked. Scientists have concluded that the Thaumoctopus mimicus uses this mimicking as a defense mechanism because it allows predators to believe the mimic octopus is a venomous predator who they do not want to mess with.

How close the mimic octopus is to the ground or the surface of the water is one of the determining factors as to which predator the octopus decides to mimic. Other factors that affect its choice of animal is the speed the octopus is moving and the other creatures currently around the octopus. During Finn’s 24 hour period of observation, the study found the mimic octopus mainly impersonated 4 main different animals, all which were venomous predators that lived in the environment, displayed below.

Flatfish Figure 3. The different forms the Thaumoctopus mimicus mimics

When moving right along the ground at a faster speed than crawling, the octopus would draw in all its arms into a leaf-shape, with a central mantle trailing behind the head (Figure 3c.) The octopus would undulate its body while in that shape, representing a flatfish (figure 3d) (Norman, 2001.) This mimicking technique was observed in the study “Mimicry and foraging behavior of two tropical sandflat octopus species off North Sulawesi, Indonesia” conducted by R. Hanlon, L.A. Conroy, and J. Forsynthe. This study found that the flatfish mimicking technique is used to move longer distances, at a faster speed.

Lionfish

During Norman’s study spectating the mimicry of several mimic octopus, they sometimes would observe the octopi just hovering above the sea-floor with arms trailing from the side of their body. This appearance was similar to that of the lion fish, a fish with venomous spines who were fully flared (Figure 3e and 3f.)

Sea Snake

There have been many times when divers researching the Thaumoctopus mimicus, and accidentally mistook it for a sea snake. The mimic octopus will push six of its arms into the sand, and spread the other two straight out from one another, moving them back and forth slightly. During this time the octopus will pull its head as close to its body as possible, giving the appearance of a sea snake (Norman, 2005.) This can be seen in figure 3g and 3h. They observed this behavior occurring when there were small territorial Damselfish, common prey of sea snakes, pestering the mimic octopus. The octopus decided to mimic the sea snake, thus scaring off the damselfish (Norman, 2005.)

Jellyfish

Habitat

Their environmental habitat tends to be fairly common. They appear to prefer warmer waters and muddy locations, making this species harder to locate via diving. They tend to be located in these sandy and muddy substrates off of river mouths or estuaries that are roughly 2-12 meters deep (Norman, 2001.) After observing these habitats, they found that it is “rich in benthic infauna” and has several different worms, echinoderms, crustaceans, and fishes, all which the mimic octopus consume (Norman, 2001.) In shallow waters there are not many places to hide from predators; some researchers believe this is why the mimic octopus has developed the ability to "mimic" different venomous species that co-live in the area

Figure 2. Mimic at rest Resting

During the study “Dynamic Mimicry in an Indo-Malayan Octopus” conducted by M. Norman, J Finn, and T. Tregenza, mimic octopuses were filmed over a 24 hours period on a research dive. This study found that the mimic octopus displayed a variety of postures and body patterns depending on whether or not the octopus was moving. When at rest, the mimic octopus typically sits in the mouths of burrows on sand mounds, with all of their tentacles under the sand (Figure 2 and 3a) (Norman, 2001.) This helps the octopus blend in with the mound and environment. Like other cephalopods, the mimic octopus is capable of changing the texture of its skin, the pattern, as well as the color to camouflage into its environment. In the sand mounds, the octopus tends to mimic sponges, coral, and different plants found in these murky shallow waters. However these are not the only objects the mimic octopus will represent. They have been known to mimic different animals such as anemones or starfish. During Norman’s study, observation of the first captured Mimic octopus found it mimicking a large sand anemone by raising all the arms above the body, each being held in a zig-zag form (Norman, 2001.) There has also been photographic evidence presented by J. Nabhitabhata and C. Sukhsangchan in their article “New Photographic Record of Mimic Octopus in the Gulf of Thailand” that shows a Mimic octopus impersonating a brittle star while resting, seen in Figure 3b. As seen, there are several different camouflaging techniques the mimic octopus uses to blend into its environment while at rest.