Advertising Toxicity to Defend Against Reef Predators

Although chemical defenses can provide excellent protection for many reef organisms, there is always a danger that an inquisitive predator might launch an attack before realizing its mistake. Although this may have dire consequences for the attacker, the prey animal may also suffer serious injury. Therefore, it pays for animals to advertise their toxicity clearly, making sure that predators get the message well before they become too interested.

Do all inedible animals advertise?

Whereas the most dangerous animals usually do invest in warning colors, there are many species that, for whatever reason, do not. Marine sponges are soft bodied and highly vulnerable to fishes but those that live among high densities of fishes, such as coral reef sponges, are almost always unpalatable to fish. On the whole, sponges do not use bold warning colors to alert their predators, possibly because they are able to regenerate damaged tissue. But even without these warning colors most fish rarely attack them and even avoid eating fragments of sponges. This may be because the sponges also smell bad or because the fish simply learn to avoid them after an early encounter.

What color patterns do poisonous animals use as warning signals?

In biological terminology, using color patterns to warn potential predators of danger is known as aposematism. Most poisonous animals are aposematic the deadly blue-ringed octopus uses a subdued, camouflaged color pattern for most of its life, but when threatened it flashes the vivid blue warning pattern that gives it its common name. Similarly, the devil scorpionfish blends in with its background under normal conditions, but when threatened it produces a display to warn its assailant of its toxic qualities.

However, a warning signal is only effective when it can be generally recognized. For this reason, groups of poisonous animals all tend to converge on the same kinds of signal; for example, many stinging insects, such as bees and wasps, use the combination of yellow and black to give advance warning. The same happens on the reef, where different nudibranch species all adopt the same livery to consolidate the message to any potential predators, a phenomenon known as Mullerian mimicry.

Are warning colors mimicked by other reef animals?

When large groups of poisonous animals all use the same warning colors to signal that they are poisonous and should not be interfered with, it sends a strong message to their potential predators. But, rather sneakily, the message can be hijacked by perfectly harmless animals that merely pretend to be poisonous.

For example, hoverflies have exactly the same color pattern as wasps but are completely inoffensive; this is known as Batesian mimicry. In effect, the harmless creatures use the wasp's color pattern — pretending to be
dangerous without actually being so — to protect themselves. On the coral reef, predators avoid the valentine pufferfish and with good reason — it is extremely poisonous. But the blacksaddle filefish (Paraluteres prionurus), a completely harmless species, gains protection simply by looking like a valentine pufferfish. However, predators are not stupid; this bluffing strategy only works when there are comparatively few mimicking cheats relative to the number of real poisonous species, otherwise the predators would quickly leam and start to attack