In our previous installation of reef creatures and their survival techniques, we talked about mimicry and how certain mimics have evolved to copy their models for protection. In this second part, we take a look at animals who display protective resemblance. Protective resemblance is a passive form of mimicry where an animal copies an inanimate object to remain hidden and under the radar – A.K.A, camouflage. Like a stick insect and his stick, or a leaf insect with his leaf leaf, the reefs are filled with creatures that look like things they aren’t suppose to look like. Take a look at the photo above of an Antennarius frogfish in camouflage. The reef is a large continuous structure replete with rocks and sponges and while it may be easy to find it here, down there it is a whole different story.
Fishes that adopt camouflage for cover and concealment have two main purpose. Like in aggressive mimicry, some use camouflage in an incognito attempt to sneak up on their prey for the element of surprise. Others use protective mimicry to blend in with their surroundings and hide, to increase their chances of survival by decreasing their visibility.
There are many masters of camouflage in the reefs, each specialising in their own field of disguise. No two are ever the same, and they are patient predators waiting in ambush. The antennae frogfish is (Antennarius sp.) are some of the best sponge impostors anywhere in the ocean. Each individual is structured differently from another, and are rugose with knobs and nooks and undulated with textural contrast. They come in a rainbow of colours with an endless pattern of permutation to suit their spongey habitat, and some are capable of colour change.
The individual above mimics an orange sponge and you can see just how well it carries that out. The outline of a typical fish is broken by knobby and stumpy fins, and the body colour is replete with darker patches and blotches to mimic the many osculum (openings) in a sponge. Frogfish are not good swimmers, and are well known for their limb like pectoral and anal fins which they use to moonwalk clumsily around the reefs. As such, they do what they do best and sit. And wait, for a small unfortunate fish to swim by and then the rest as they say, is history.
Taking the silhouette dissolving game even further is the weedy scorpionfish, or Rhinopias frondosa. These ambush predators, like the frogfish, spend much of their lives sitting around waiting for food to swim by. In order to do this they have to be pretty darn good at camouflage, and they definitely are. While some species of Rhinopias can pull off as a rather convincing sponge, the weedy scorpion fish uses a filamentous macro algae disguise as is modus operandi.
All its fins, as well as its body, mouth and ocular grooves are festooned in filamentous extensions that resemble the leaves of many macro algae, such as Gracilaria. As if this wasn’t convincing enough, the extensions are soft and pliable, and move with the flow of water. Rhinopias frondosa come in an array of patterns, colours and forms. Some prefer looking like filamentous algae, while some prefer stocky leafed varieties. Regardless of their MO, they are excellent at their art and make for very convincing “algae”.
Here’s another example of a weedy scorpionfish, this time in brown. Check out the filamentous fronds and extensions. This one is even more exaggerated than the one before. Pay close attention to its surroundings. Unlike the previous photo, this individual lives in an area where colourful macro algae may be sparse. The brownish clump in the foreground is mimicked perfectly by the fish, and in a a macro photograph it may still be easy to identify. Extrapolate the photo to its macro surroundings and the fish becomes invisible.
Another ambush predator that disguises itself is the well known and iconic stone fish. What better disguise to choose than stones, which is probably just as abundant and the second best thing to copy after water. Honestly though if a fish could mimic water, that’s severely rigged and just plain cheating. We chose a photo of a stonefish in an area devoid of stones to make it easy for you to find, but even then it puts up a really convincing decoy. In a vast rubble reef filled with nothing but rocks, a stonefish in ambush is one of the hardest things to find. Literally, it’s like finding a hay in a haystack. You read that right.
Unfortunately because the stonefish’s disguise is so good, people often run the risk of stepping onto them. Apart from their predatory cunningness, the stonefish has also highly venomous spines on its dorsal fin. These envenomated spikes can deliver an extremely painful reaction when accidentally stepped on.
While camouflage is good for sneaking up on prey, it is also just as good for concealing yourself from said predator. The ghost pipefishes from the genus Solesnostomus are practically inventors of this game, and are some of the most crazily talented artists in their field. The robust ghost pipefish, S. cyanopterus above is an excellent mimic of seagrass. Not only are they tapered and compressed, each individual has its own set of leaf like realness that help shy them away from even the most eagle eyed macro photographer.
Translucency in a dying leaf and natural brown streaks are just some of the many leaf like qualities that the robust ghost pipefish is capable of mimicking. Some are coloured brown to mimic a completely dead leaf. Because these are not situated directly on the seafloor, they are susceptible to wave movement and current. As such apart from their physical form, their swimming style has to correspond to their disguise as well. Ghost pipefishes hover in the water very close to their models and sway in the same way they do. For the robust ghost pipe fish, that means staying close to its sea grass and swaying with it.
An even more amazing species of ghost pipefish is the halimeda ghost pipefish. Solenostomus halimeda mimics the calcareous halimeda algae in pure perfection. Halimeda is a calceous algae with a calcium carbonate frame, and each cuboidal “leaf” is connected on end to form a chain. As the algae dies, it leaves behind a white calcium based “skeleton”. The halimeda ghost pipefish copies it remarkably well, with its fins and tail looking almost perfectly like the cuboidal leaf structure of Halimeda.
Not only is the physical form convincing, the ghost pipefish is also green with intermittent streaks of white to mimic dying portions of the algae. All ghost pipefishes have a diet of small crustaceans and various kinds of amphi- or copepods. They hunt for their prey around the structures that they mimic and seldom stray far. Another wonderful species is S. paradoxus, the ornate ghost pipefish. That species has frilly filamentous appendages which it uses to disguise itself in Crinoids and various sea fans.
Fish are not the only one who use camouflage. Invertebrates are just as, if not more adept at cover and concealment than their vertebrate friends. In the invertebrate world, everything wants to eat you. If you’re a crab, you’re food. If you’re a cuttlefish, you’re food. If you’re a shrimp, you’re also food. Needless to say invertebrates are cunning little creatures that make use of camouflage pretty well too.
Halimeda is apparently very popular. Everything wants to copy it, and rightfully so. Being calcareous, Halimeda is not easy to eat nor is it palatable. As such it would make a good object to copy. The halimeda crab, Huenia heraldica is another master of disguise. Not only does it look like it with its green and irregularly shaped body, it goes the extra step by cutting pieces of halimeda and sticking it on its rostrum. The crab above has a long piece of Halimeda stuck on its head, completing its deception perfection.
Another class of invertebrate with impeccable deceptive qualities are Nudibranchs. The xenia nudibranch Phyllodesmium rudmani is one of the best. The slug is adorned all over with appendages mimicking a Xenia polyp. These nudibranch prey on Xenia and when feeding on the coral, are nearly invisible. Even when they are not on the coral and just crawling on the sand bed, they look like a lonesome Xenia colony.
To list every invertebrate or fish with a camouflage quality would be a tedious and improbable task. This short article with a few examples help highlight the various ways of camouflage and how it helps them stay protected, or to keep them concealed while hunting. Of course there are many more amazing examples such as the octopus, and these are just some of the many clever animals that live to fight another day in the ever dangerous reef they inhabit.