Flounder Mimicry in an Atlantic Octopus

Octopuses are well known for their ability to camouflage with their environments and, at times, mimic other marine species. A lack of rigid structures in their bodies makes them extremely malleable while command of their coloration allows them to easily blend in with their environments. Muscular and freely bending arms allow them to move in a variety of different ways. These features all contribute to the ability of some octopus species to use mimicry as a method of defense and survival.

 A study published by Hanlon, Watson, and Barbosa describes the first instance of documented flatfish mimicry in an Atlantic octopus species. A few examples of mimicry in octopus species had been observed previously, but the species involved had all been located in the Pacific Ocean rather than the Atlantic. The octopus Macrotritopus defilippi is Caribbean octopus that can be found in sand plains where little shelter is available. Growing up to 90mm in length, details about the biology and life history of this species remain elusive. Over the course of several dives, M. defilippi was observed in five different locations mimicking posture, style, and speed and coloration of a common flounder, Bothus lunatus.

M. defilippi

Octopuses – and other animals that use camouflage – can blend in with their environments as long as they stay still, but movement will alert predators to their presence. While some octopus species can work around this using slow movements in a dense and structured environment (such as a coral reef), M. defilippi has no such luxury. This species faces the challenge of needing to navigate a wide and open habitat without being detected. By combining camouflage and mimicry, M. defilippi can safely cross the sand without raising suspicion.

Figure 1: Examples of M. defilippi using mimicry in its movement.

Using gathered video data, the swimming speed and style of M. defilippi was compared to B. lunatus. The flounders have a distinct swimming style in which they swim along the contours of the sand, hugging the ripples. The octopuses copied this style, swimming along the shapes of the sand just as the flounders did. The octopuses also positioned themselves in such a way that their eyes were in a position similar to where the flounders’ would be. A M. defilippi octopus captured during its planktonic stage and raised in captivity in 1978 with no exposure to flounders exhibited identical swimming behavior, indicating that it is instinctual rather than learned.

Up to this point, octopus defense strategies against predators have been categorized into three stages. First is using camouflage as a primary defense, second is using sudden and startling displays when closely approached by a predator, and third is attempting to escape using erratic movements that will confuse the predator. With camouflage being the primary defense mechanism, developing a method that can maintain the illusion during quick movements is both important and difficult. The authors believe that M. defilippi being the third recorded octopus species to utilize flatfish mimicry means that using mimicry along with camouflage may be more common than previously thought and should thus be added to the category of primary defense.

Hanlon, R. T., Watson, A. C., Barbosa, A. A 'mimic octopus' in the Atlantic: Flatfish mimicry and camouflage by Macrotritopus defilippi. The Biological Bulletin 218:1 (2009). 15-24.
http://www.journals.uchicago.edu/doi/full/10.1086/BBLv218n1p15