Coloration of reef organisms
 
column spacer Coloration of reef organisms
  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 icons.
 
 

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 as a 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: pattern disruption

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of yellowtail snappers

One would think that bright colours in fishes that prey on other fishes would be counter-productive as they would alert their own predators. However, as seen in these yellow-tail snappers, the colour-pattern may be visually disruptive in the eyes of the prey. - Little Cayman 2003

NOTE Ocyurus chrysurus

 
 

photograph of a banded butterflyfishAbout 20% of all Caribbean reef-fishes have disguised eyes, either obliterated, broken-patterned, or eye-barred. Eye-bars disrupt the visual continuity of an animal, helping to disguise it from its predators. Eye-bars are a common type of defensive coloration in other animals as well, including many birds and mammals. Over 90% of all world species of butterflyfishes, genus Chaetodon, have some sort of eye-marks or eye camouflage, or have entirely black faces.

NOTE it's interesting that the eye-bars of C. stiatus, shown here, only half cover the eyes...from this we must conclude that, unlike half a wing, evolution of half an eye-bar has selective value

Banded butterflyfish Chaetodon striatus with eye bars 0.4X

 
photograph of hogfish in company with trumpetfish and bar jack photograph of spotfin butterflyfish

A hogfish Lachnolaimus maximus forms a cooperative hunting group with a trumpetfish Aulostomus maculatus and a bar jack Carangoides ruber. The hogfish's eyes do not
seem to be particularly well-camouflaged against the dark head stripe until you recall that the flash photograph has restored red wavelengths. At depth, owing to the quick attenuation of red wavelengths, the eyes would appear black to other fishes 0.3X

Spotfin butterflyfish Chaetodon stiatus bearing a camouflaging eye-bar. The spot on the fin is thought to be an eye mimic, a topic considered in the MIMICRY section of function of colours 0.75
 
 
 

Eye-bars on predatory fishes may function both to disguise them from their prey and to confuse their own predators.
photo array showing various predatory fishes with eye-bars
 
 
 

photograph of the head of a Nassau grouper
The split-head colour pattern on a Nassau grouper Epinephelus striatus divides the head into halves and disrupts its outline. A split-second delay in recognition by the intended prey of the grouper may be all that is required for the grouper to eat it.

 

 

 

 

 

Nassau grouper Epinephelus striatus 0.5X

 
 

photo array showing different configurations of eye-bars in Caribbean reef fishes
If eye-bars act to hide the eyes and confuse the viewer, what explains the brightly coloured and apparently conspicuous eyes of many other reef fishes? Since such conspicuous eye-coloration often includes combinations of black, blue, and yellow - colours that transmit well through clear reef waters - it is thought that they could be functioning not for pattern disruption, but as intraspecific signals. Thresher 1977 Z Tierpsychol 43: 152.

NOTE lit. "within species", and therefore having a social type of function. For more on this topic see FUNCTION OF COLOURS: SOCIAL

 
  photographs of life stages of blue tangs Acanthurus coeruleus
As another example of this phenomenon, even though the function is not actually known, body colours of blue tangs go from yellow to blue during development, while iris colours surrounding the black pupils go from blue to yellow. Thus, the 3 "easy-to-see" colours, also referred to as "poster" colours, are maintained through development. Thresher 1977 Z Tierpsychol 43: 152.

 
 

Categorisation of colour combinations and patterns in 51 reef-fish species in Hawai'i show that the 3 most common groupings are:

1. yellow and orange with blue,
2. yellow with black, and
3. white with black.

The authors of the study suggest that these combinations are ones that transmit well close up, thus possibly providing sexual or territorial information, yet form strong disruptive patterns at a distance, providing camouflage. Marshall et al. 2003 Copeia (3): 455.

A simulation of this is provided below for a bluehead wrasse Thalassoma bifasciatum. Note the change in visual obviousness of the colours of the wrasse at different distances.

 
photograph 1 in a series of 4 of bluehead wrasses at different distances photograph 2 in a series of 4 of bluehead wrasses at different distances photograph 3 in a series of 4 of bluehead wrasses at different distances photograph 4 in a series of 4 of bluehead wrasses at different distances
 
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