Camouflage – The Art of Disguise

Camouflage and its countermeasures are some of the most challenging visual games played out in the ocean. An animal searching for its next meal needs to be able to detect and approach it without scaring it, whereas for the impending meal it generally pays to stay hidden.

This plays out an endless evolutionary arms race between predator and prey, and as a consequence, there are a myriad of beautifully refined ways to camouflage underwater.
The most obvious means of camouflage is to blend into the surrounding environment, and this technique (called crypsis) is ubiquitous across most marine taxa, from fishes to all manner of invertebrates.

Cryptic colouration is the most common way of achieving this, by possessing colours and patterns that match the common background, such examples in New Zealand waters include the many juvenile reef fishes or the mottled kelpfish and marblefish.

Even more complex is active crypsis, a changing of the colour and/or texture of the skin as the animal moves between different habitats and backgrounds. Chromatophores are responsible for this, whereby swiftly translocating pigments or reorienting reflective plates in these cells brings about rapid colour changes. Many fishes such as scorpionfishes and flatfishes are capable of this. However, it is cephalopods such as octopuses that are masters of this disguise, and have such control over their complex chromatophores that colours can pulse exceedingly fast, so much so that it is also used for signalling.

Cryptic camouflage is not only used for defence, but also attack. Sit and wait predators like scorpionfishes, flounders and stargazers often have the most elaborate camouflage patterns. This enables them to get within striking range of their completely unaware prey. Moreover, it is these types of predators that are associated with some of the fastest movements in the animal kingdom, as they strike out to ensnare a passing meal.

In open water, there are no complex backgrounds with which to hide against, therefore camouflage is approached entirely differently.

There are four main types of open water camouflage – transparency, countershading, illumination and reflection. Transparency is generally the domain of small-bodied zooplankton such as jellyfish and larval animals. Although complete transparency is effectively impossible, by achieving transparency in most body parts, these animals can remain undetectable in the ocean. In the well-lit surface waters, predators can see easier than in deeper water. This means to remain transparent there, much more of the body has to be clear (ie. jellyfish can be over 90% transparent), resulting in large gelatinous bodies that float near the surface – usually a trade off in mobility for the extra transparency. Countershading (otherwise known as Thayer’s Law) is a common mechanism in pelagic fishes and cetaceans.

By being dark on top and light below this makes the animals disappear into the background whichever way something is looking at you. When something looks down into the inky darkness, or up towards the brightly lit surface the counter-shaded animal effectively disappears. This protects vulnerable prey items, but also facilitates in hunting. For instance, impact predators like kingfish rely on their countershading camouflage to delay their prey’s detection, allowing them to get within striking distance. Illumination, or more specifically, counter-illumination, is also a common feature of camouflage.

Animals use bioluminescence to create a similar effect to the countershading above, with symbiotic bacteria such as <<<vibrio>>> found among fishes, cephalopods and other invertebrates. However, this is more common in the darker deeper waters, beyond the realm that most of us can venture. Reflection is a clever mechanism of, well, simply reflecting light. The reflections, usually from the sides, make the object show as a reflected patch of the environment (eg. water column). This means of camouflage is very common and successful in smaller pelagic and schooling fishes.

There are countless other mechanisms of camouflage, including irregular shapes to break up an outline, concealment of a shadow, disruptive colouration or false eye spots to distract and confuse would-be predators. Self-decoration is another active means of crypsis. Decorator crabs in New Zealand Notomithrax sp. stick sedentary objects – often living, such as algae and sponges – to its shell to provide camouflage. Mimicry is yet another example of natural selection crafting a fascinating means of camouflage. By disguising as something else, this affords a would-be prey some protection, say as something unpalatable or toxic. It also provides animals with ulterior motives a chance to gain the trust of unsuspecting animals, a common ploy for cleaner wrasses and mimic blennies.

Going unnoticed provides an obvious advantage and increases an animals’ chances of survival, either hiding from predators or facilitating a meal.
As such, camouflage is ubiquitous in the natural world. Underwater there is evidence of it in almost every direction; be it hidden in the reef, in the dark inky depths, or even in plain sight in the sunlit surface waters.