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, camouflage, 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: camouflage: vertebrates

 

We know from other parts of the VIRTUAL DIVE that camouflaginig in reef organisms can involve combinations of colour, form, and behaviour. What follows in this section are some examples where colour and colour-patterns predominate. This topic is divided into vertebrates, considered here, and INVERTEBRATES, dealt with in another section.

NOTE see DEFENSES OF FISHES: AVOID DETECTION: CAMOUFLAGE

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs photograph of a shoal of blue tangs feeding taken from a video

"Wow! Here's a bunch of hungry blue tangs, but who's this sneaking through the group? Trumpetfishes like to use other organisms as camouflage as they move around the reef, sometimes not too successfully...as we see here." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Acanthurus coeruleus

NOTE Aulostomus maculatus

 
 


Peacock flounders attack small fishes, octopuses, and shrimps from camouflaged positions in the sand. Abundant chromatophores produce colour and pattern change within moments to match the fish's background.

photograph of a peacock flounder Bothus lunatus camouflaged in the sandHow does this work? Well, the chromatophores themselves are not sensitive to colour or pattern, nor do the eyes somehow transmit a "photographic" image of the colour pattern of the substratum to the brain to transmit to the chromatophores. The exact mechanism is not well understood, but what is thought to happen is that the skin and to some extent the eyes perceive the ratio of incident light (directly from the sun) to reflected light (from the substratum) and communicates this, skin-section by skin-section, to the brain and thence to the chromatophores. When resting on a checkerboard, some flatfishes can recreate the white and black squares in perfect size and orientation with those on the board.

NOTE function of chromatophores is considered in more detail at COLORATION OF REEF ANIMALS: HOW COLOURS ARE CREATED: CHROMATOPHORES

 

Peacock flounder Bothus
lunatus
resting on sand 1X

  What more can we learn about camouflaging in peacock flounders? Study these photos in relation to how well the flounders are camouflaged on the different backgrounds, and see what ideas you come up with. The comments below each photograph may be useful if/when you get stuck.
 
photograph of peacock flounder Bothus lunatus camouflaged 1 photograph of peacock flounder Bothus lunatus camouflaged 2 photograph of peacock flounder Bothus lunatus camouflaged 3
Typical coloration of a peacock flounder on light-coloured sand. In addition to chromatophores, this species has pigment spots on its midline and on the peripheral fins. Note that the spots seem to be reduced in relative size in comparison with the other 2 flounders shown here Why has the flounder selected this unusual coral location on which to rest? Note that it has accentuated its pigment spots and created others by expansion of melanophores (colour cells containing black melanin pigment). This creates a better match with the black spots on the coral This flounder similarly appears to have accentuated its black spots to match the pattern of black stones in the sand. Did it preferentially select this dark-spotted area of sand because its permanent dark pigment deposits would make for good camouflage?
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of initial-phase stoplight parrotfish

"Initial-phase parrotfishes often have a light or chocolaty checker-board coloration that is quite different than the bright colours of terminal-phase males.. Sexual recognition do you think? Or maybe just disruptive camouflage for the bottom-inhabiting juveniles?" - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Sparisoma viride

 
 
photographs of life stages of stoplight parrotfishes Sparisoma viride Juveniles of many species of coral-reef fishes are more cryptically coloured than the adults, and they tend to hang out closer to the sea bottom, thus adding to the camouflaging illusion. photographs of life stages of princess parrotfishes Scarus taeniopterus
 
 

photograph of squirrelfish Holocentrus adscensionis
In fishes, solid colours that seem bright to us may be for camouflaging. Squirrelfishes and cardinalfishes that inhabit recesses and caves, and/or that hunt at night, are less visible in dim photograph of squirrelfish Holocentrotus rufuslight because of their red colours. Not only do red wavelengths rapidly diminish with increasing depth, but fishes are apparently relativey insensitive to red wavelenghts. Marshall et al. 2003 Copeia (3): 467.

 

Squirrelfish Holocentrus
adscensionis
0.6

 

Longspine squirrelfish
Holocentrus rufus
0.6X

  Blackbar soldierfishes Myripristis jacobus emerge from protective hideaways at dusk to begin a night's foraging. As the light fades into twilight, their red colours not only dim in intensity, but gradually become washed out.
 
photograph 1 in a series of 5 showing twilight effects on red colour of blackbar soldierfishes Myripristus jacobus photograph 1 in a series of 5 showing twilight effects on red colour of blackbar soldierfishes Myripristus jacobus photograph 1 in a series of 5 showing twilight effects on red colour of blackbar soldierfishes Myripristus jacobus photograph 1 in a series of 5 showing twilight effects on red colour of blackbar soldierfishes Myripristus jacobus photograph 1 in a series of 5 showing twilight effects on red colour of blackbar soldierfishes Myripristus jacobus
  LATE AFTERNOON           DUSK  
 
  photo array of a few Caribbean reef fishes that have yellow coloration
Many species of reef fishes, in either or both juvenile and adult phases, bear distinctive yellow colorations that are conspicuous close up, but from a distance may act as camouflage.

 

 

 

 

 

 

 

 

 

 

 

 

 

  simulation of a queen angelfish
This is simulated in the 2 photographs shown here of a queen angelfish Holocanthus ciliaris, one with the fish close up; the other, with it in the distance.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of jacks swimming in a loose shoal

"See how these horse-eye jacks are bright, then dark, depending upon how the surface light hits them. If they were to move quickly in this way, it's easy to see how a predator might be confused." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Caranx latus

 
 

photograph of a school of silversides in a mangrove area
The bewildering pattern a school of silversides presents to a potential predator is not just confusing, but is also a kind of camouflage, because when the fishes swim close to the sea surface the reflections seen by the viewer are actually of the bright sea surface.

 

 

 

School of silversides at the
edge of a mangrove area 0.15X

   
 
To understand how mirror-sided fishes are camouflaged, imagine that you are looking up to the sea surface during a dive... drawing 1 in a series of 4 to show how a silversided fish's camouflage works
...from your pocket you bring out a piece of transparent glass and look through it to the surface...and the glass, of course, appears to disappear... drawing 1 in a series of 4 to show how a silversided fish's camouflage works
...now you bring out a small mirror and hold it out and look into it as you did the glass... drawing 1 in a series of 4 to show how a silversided fish's camouflage works

...and, if you now tilt it to the correct angle, the mirror also appears to disappear because it reflects a portion of the sea surface.

This is the principle governing the reflective camouflaging of mirror-sided fishes such as silversides, and silvery types of other fishes, such as salmon and herring.

drawing 1 in a series of 4 to show how a silversided fish's camouflage works
 

 
drawing of head of a silvery-sided fish showing how platelets function to reflect light


Such fishes have a myriad of essentially tiny reflective mirrors called platelets embedded in the skin and scales. The platelets are laterally compressed and are embedded vertically even in the round parts of the body, thus aiding in the mirror-effect.

NOTE lit. "small plates". The platelets contain deposits of white reflective guanine, a purine base representing a component of RNA and DNA

photograph of a herring 3 rotational views
  Some fishes, like ambush-hunting scorpionfishes Scorpaena plumieri, put more reliance on body texture and motionless behaviour, than on colour, to be camouflaged, but all are important components in the illusion.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a scorpionfish hiding in the seaweeds taken from a video

"Let's just swim slowly up over this tangle of seaweeds...I thought I saw an eyeball...but let's make sure. Yes, it's a spotted scorpionfish in hiding...good camouflage, don't you think?

NOTE Scorpaena plumieri

 
  In other species of reef fishes colours, even some of the brightest ones to our eyes, can provide effective camouflaging depending upon the habitat that the fish happens to be in. Scientists in Hawai'i compare spectral reflectivity patterns, that is, overall colour patterns, of different parts of the reef environment with the different colours and colour combinations of the inhabitant fishes. The following sets of panels show how this might work for a few Caribbean species. Each resident species is shown in different parts of its habitat, and there are explanatory comments from the scientists who did the studies. Marshall et al. 2003 Copeia (3): 467.
 
photograph of blue chromis photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background
NOTE: blue fishes like this blue chromis Chromis cyanea are best camouflaged against a deep-water background
 
photograph of a stoplight parrotfish
photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background
NOTE: green fishes like this stoplight parrotfish Sparisoma viride match to horizontally viewed space just at or above the reef top
photograph of a trumpetfish photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background
NOTE: a yellow-coloured trumpetfish Aulostomus maculatus is poorly camouflaged in shallow reef areas because our eyes distinguish yellow from other reef colours quite easily. A yellow fish against a deep-water blue background is especially conspicuous because the 2 colours are close to being complementary (i.e., contrasting)
 
 
photograph of a redband parrotfish Sparisoma aurofrenatum
photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background photograph of a blue chromis possibly camouflaged against an area of reef background
NOTE: combinations of reds with greens or blues, as in this initial-phase redband parrotfish Sparisoma aurofrenatum, will camouflage the possessor in shallow-water habitats where reds are still visible to predatory fishes or, in even shallower habitats, to predatory wading-birds
   
 

REVIEW: from the comprehensive studies on functions of colours in Hawai'ian reef fishes, what do we know thus far on general camouflaging and pattern-disrupting coloration in reef fishes? Marshall 2000 p.83 In, Animal signalling. Signalling & signal design in animal communication (eds, Espmark et al.); Losey et al. 2003 Copeia (3): 433; Marshall et al. 2003 Copeia (3): 455; Marshall et al. 2003 Copeia (3): 467.

1. Colours and colour patterns are multipurpose. At close range they may be for social communication, such as sexual or aggressive messages between conspecifics, and at distance provide pattern-disruptive camouflage against predators.

2. Many reef-fish colours have a UV-reflective component, so there may exist the potential for a "secret" level of communication between fishes. The caveat to this is that less than half of all reef fishes in Hawai'i have UV sensitivity, and there appears to be no correlation between the UV-reflectance of a species and its own ability to see images in UV.

3. Finally, the fact that many reef fishes appear not to be able to see in UV suggests that use of UV by certain species to "send out" anti-predator "messages" or territorial advertisements would be uninterpretable by many fishes because they can't see in UV.

NOTE for most benefit from this "review" you should have also looked at 2 other sections: COLORATION IN REEF ANIMALS: HOW COLOURS ARE PERCEIVED

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photgraph of dolphins swimming taken from a video

"Oh, some nice bottlenose dolphins joining us for our dive. Can you see their counter-shadings? Most sharks and cetaceans are counter-shaded for camouflage...but against what?...maybe bigger sharks, or perhaps killer whales where they occur? Hawksbill turtles are doubly protected...counter-shading for camouflage and heavy shell plates to resist crunching teeth." - 2002 Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Tursiops truncata

 
  photo array showing countershading strategies in coreal-reef fishes
Counter-shading, that is, dark on top and light on the bottom, provides camouflage both against predators looking down and predators looking up. Many Caribbean reef fishes, even though brightly coloured for possibly other reasons, are counter-shaded for camouflage.
 
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