Coloration in reef organisms
column spacer Coloration in 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, considered here, the latter including the possibility of UV protection. 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. CLICK ON a topic to learn about it.

Function of colours: defense: warning of toxicity: introduction


We know from other parts of the VIRTUAL DIVE that camouflaging 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. We know from other parts of the VIRTUAL DIVE that camouflaging in reef organisms can involve combinations of colour, form, and behaviour. In considering the topic of warning of toxicity we will see examples where colour and colour-patterns predominate. This large topic is divided into an introduction section presented here, and sections on


seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of colorful reef fishes "I wonder if these fishes are toxic in some way and their bright colorations are warnings to other fishes? Eat me if you dare!." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize

photo collage showing colorful and sometimes toxic reef organisms
Any brightly coloured animal that openly wanders the reef or that is otherwise visually obvious is a candidate for "warning-colour" status, but the problem is in knowing what toxins, if any, it may have, and what predatory animals the toxins may be acting against. Photo of clown crab courtesy John Lewis, Montreal.

NOTE also known as aposematism lit. "away" "sign"

NOTE many or most xanthid relatives of the clown crab Platypodiella shown here are distinctively coloured, and many are known to possess deadly tetrodotoxins of the type found in puffer fishes

  With a some exceptions, so little is known about the biology of reef invertebrates that we can only guess at the function of their coloration. There is evidence that the flesh of some Caribbean tunicates is toxic and some, like the ones featured below, are certainly colorful, but little is known about possible predators.
photograph of an unidentified tunicate photograph of strawberry tunicate Eudistoma sp. photograph of bluebell tunicates Clavelina puertosecensis
Unknown tunicate 1X Strawberry tunicate Eudistoma 2X Bluebell tunicate Clavelina puertosecensis 0.2X

photo array of 2 types of reef invertebrates that come in colour morphs
Where a species comes in different colours, it seems unlikely that it will be toxic. The reasoning for this is that if the colours were for warning, potential predators would have a confusing and likely impossible time learning to associate all the different colour morphs with a common, easily remembered, toxic entity.

NOTE neither species shown here is known to be toxic. The reasoning used above is a bit "circular", but the idea is basically sound

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of queen angelfish "Not all brightly coloured reef inhabitants are advertising toxicity, at least not in ways that we can determine. One problem in devising experiments to test for function of coloration is that we may have only a sketchy idea what the predator of an organism might be." - Turneffe Island, 2002. Video courtesy Andy Stockbridge, Belize.

photograph of a cushion star  to show spinynessphotograph of a black crinoid Nemaster grandis
Not only do we not know what predators a certain reef organism might have, but their coloration may have evolved in response to selective factors no longer present, with the colours being retained possibly through genetic linking with other currently useful features. Also, is it possible that warnng colours could be associated not with toxicity as such, but with some other distasteful feature(s), such as spinyness?

Crinoid Nemaster grandis 0.2X

Cushion sea star Oreaster


Still, there are many reef animals that are toxic and that may be using warning colours to send a "don't eat me" signal to potential predators. Recognition of such signals by a predator is thought not to be innately determined, that is, with a genetic basis, but must be learned. Thus, after a predator takes a bite of a toxic prey, it becomes sick and learns not to eat others of the same prey species. The bright colours make the recognition process easier for the predator.


hot button for how colours are created part of BCCR hot button for how colours are perceived part of BCCR hot button for functions of colours part of BCCR