Coloration of reef organisms
 
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  hot buttons for colours section of Biology of Caribbean Coral Reefs website
This section deals with the function of colours. Topics of HOW COLOURS ARE CREATED and HOW COLOURS ARE PERCEIVED can be accessed via the icon.
 
 

Function of colours

  Functions of colours and colour patterns in reef animals fall into 2 broad categories of SOCIAL and DEFENSE, one topic of the latter, mimicry, being considered here. Most or all of these topics have been mentioned elsewhere in the BCCR but, by its nature, this section on FUNCTION OF COLOURS pulls them together in broad summary. A third category of UV PROTECTION is also included in its own, short section. CLICK ON a topic to learn about it.
 
 
 

Function of colours: defense: mimicry

 

Mimicry is when an animal's shape and colour resemble something else in order to attract its prey, hide from its prey, hide from its predators, or to benefit in copy-cat fashion by appearing to be another animal entirely. Fishes such as frogfishes that use lures to attract their prey are employing mimicry, and colours as well as form and behaviour are involved.

This section of mimicry deals with aggressive mimicry, while other sections deal with FISHING LURES & CAMOUFLAGE MIMICRY, EYESPOT MIMICRY, and BATESIAN & MULLERIAN MIMICRY.

 
 

Function of colours: defense: mimicry: aggressive mimicry

 
 

Some types of mimicry, such as eyespot mimicry and camouflage mimicry, act passively in defense; hence, are termed "non-aggressive" types of mimicry. In contrast, an "aggressive" type of mimicry is when a predatory species evolves in colour and shape to mimic an otherwise harmless species, thus disguising itself. This allows the predator (the mimic) either to prey on the species it is mimicking (the model) or to allow it to sneak up on other prey species that do not distinguish it from the harmless and more numerous model species. Whether aggressive mimicry exists in coral-reef areas is still under debate.

Let's see how this might work using a completely hypothetical (and entirely silly) "wolf in sheep's clothing"-type of strategy, with a barracuda as the mimic and a blue tang as the model. Afterwards, we can look at some possible examples of aggressive mimicry in coral-reef fishes:

 
drawing of an unsuccessful strategy of aggressive mimicry by a baraccuda drawing showing baraccuda thinking of a strategy of mimicry to catch some blue tangs drawing of an unsuccessful strategy of aggressive mimicry by a baraccuda
No matter how stealthy is the barracuda, it never can get close enough to the school of tangs to catch and eat one It has an idea: "If only I could disguise myself in such a way to mimic a tang, I might get close enough." A visit to the local costume shop apparently isn't enough to fool the tangs; if anything, they are even more wary...
 
A behavioural scientist in SCUBA gear has been observing the barracuda and tangs, and asks the the barracuda to come along to TANG SCHOOL to discuss its unsuccessful behaviour. One of the tangs takes exception to the barracuda being invited to class and marks up the invitation sign: cartoon 1 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs
cartoon 2 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs cartoon 3 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs
cartoon 4 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs cartoon 5 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs
cartoon 6 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs cartoon 7 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs
cartoon 8 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs cartoon 9 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs
cartoon 10 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs cartoon 11 in a series of 11 where a behavioral scientist discusses aspects of aggressive-mimicry strategy with a baraccuda and a school of tangs
 
 

photograph of trumpetfish traveling in tandem across the reef with a hogfish
Trumpetfishes commonly join with other species to move around the reef. This may be another example of aggressive mimicry. From their disguised positions in the group they can attack other fishes. In addition to simply being hidden by other members of the traveling group, the disguise is improved by the trumpetfish preferentially associating with fishes of comparable size and colour, and it often matches the arch of spine with that of the accompanying fishes. Colour changes apparently can even include having a blue snout when associating with blue tangs. Aronson 1983 Bull Mar Sci 33: 166.

 


Trumpetfish Aulostomus maculatus accompanying a
hogfish Lachnolaimus maximus across the reef 0.15X

 
 
cartoon showing 2 bluehead wrasses remarking on the blue snout of a trumpetfish
  cartoon showing 2 bluehead wrasses remarking on the blue snout of a trumpetfish
 


Another example of aggressive mimicry is thought to involve initial-phase bluehead wrasses Thalassoma bifasciatum that act as cleaners of other fishes. These may be mimicked by juvenile wrasse blennies Hemiemblemaria simulus (lit. "half blenny" "imitate" L.) which are not cleaners and which usually feed on zooplankton. They are of comparable size to initial-phase juvenile wrasses with similar colours, but differ in having a prominent spot at the tail end of the horizontal black stripe. The wrasse blenny also swims by sculling its pectorals, the same as does the bluehead wrasse (most other blennies swim by wriggling-tail propulsion), and it does occupy a similar open-water habitat to that of the putative model. If it is mimicry, its function could be aggressive. First, a close resemblance to the cleaner wrasses may allow the wrasse blenny closer approach to their zooplanktonic prey in order to eat them, in which case the mimicry would be more of a camouflaging aggressive kind. Another possibility is that by resembling the cleaners, the mimic may be able to get photograph of bluehead wrasses with a client fish in a spongeclose enough to a client fish to take a nip from their fins. In this case, the mimicry would be simply an aggressive kind. A third possibility is that a resemblance to the cleaners gives them protection from being eaten by client fishes, in which case it would be an example of Batesian mimicry. A fourth possibility, of course, is that the resembance is just coincidental. Randall & Randall 1960 Bull Mar Sci 10 (4): 444.photograph of a juvenile wrasse blenny Hemiemblemaria simulus with a queen angelfish

Initial-stage bluehead wrasses Thalassoma bifasciatum cleaning a blue chromis 0.2X

Two wrasse blennies (the putative mimics)
Hemiemblemaria simulus swim around a queen angelfish (one is near the tail), while an initial-phase bluehead wrasse (the putative model) swims directly above the angelfish's head 0.25X


NOTE
in this idea, then, the resemblance allows the wrasse blenny to make closer approach to its zooplanktonic prey, which are fooled into thinking that it is harmless (the model, a cleaner fish, does eat benthic and planktonic prey, but at least some individuals obtain most or all nutrition from eating parasites from their hosts). There is one major problem with this idea. The potential zooplankton prey, small crustaceans and larval fishes, mostly rely on their transparency for protection, with a second line of defense being quick escape-swimming. It's hard to imagine that these tiny prey are able to recognise fishes visually and adjust their behaviour accordingly; rather, it's more likely that they would tend to swim quickly away from any fast-moving/attacking fish in their immediate vicinity. So, perhaps the fin-nipping
scenio is the more believable

NOTE Batesian mimicry is discussed in another section: DEFENSE COLOURS: BATESIAN & MULLERIAN MIMICRY

 


photographs of a wrasse blenny (the mimic) and an initial-stage bluehead wrasse (the model)One reason we can't pin down what kind of mimicry it is owes to our lack of knowledge about the biology of the participants, and this task is made even more difficult by the fact that the putative mimic, the wrasse blenny, is relatively uncommon. In fact, a recent analysis of this pairing along with 2 other mimicry pairings from the Indo-Pacific suggests that, rather than being an example of aggressive or Batesian mimicry, the wrasse-blenny/initial-stage bluehead-wrasse combination may represent an example of yet another kind of mimicry, social mimicry. This type of mimicry comes from the mutual attraction of two species. A wrasse blenny attracted to mingle within a shoal of initial-stage bluehead wrasses may benefit from protection from predators conferred by being in an aggregation and also by enhanced access to food shared with the wrasses. The author concludes that if the pairing is truly mimicry it is more likely to be social rather than aggressive or Batesian as originally proposed by earlier authors. Robertson 2013 PLoS1 8 (1): e54939. Photos on Right courtesy J. Adams & D. Robertson.

photograph of a possible juvenile wrasse blenny Hemiemblemaria simulus resting in a hole in a coral

 

When not swimming a juvenile wrasse blenny
Hemiemblemaria simulus may find a hiding
spot in corals or other substrata 1X

 
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