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, 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

 
 

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. This large topic is divided into a section on fishes, considered here, and sections on SEA ANEMONES JELLYFISHES & HYDROIDS, ZOANTHIDS, and SNAILS presented elsewhere.

NOTE see DEFENSES: INVERTEBRATES: BEHAVIOUR: HIDE AWAY/CAMOUFLAGE

 
 

Function of colours: defense: warning of toxicity: fishes

 
  photographs of reef fishes as part of quiz to determine which may be warningly coloured
There are lots of colorful reef fishes in the Caribbean area, but how many of them are warningly coloured? Take a moment to scan this collection of common Caribbean reef fishes, then sort them mentally into categories of WARNING COLOURS and NOT KNOWN TO BE WARNING COLOURS. Note that only the toxic ones can be "warningly coloured". Now, look at the black boxes below the video to see the fishes correctly sorted, at least based on present knowledge.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website
photograph of juvenile yellowtail damselfish

"This little juvenile yellowtail damselfish couldn't get much brighter, at least not to our eye, but I've never heard that it is warning of any sort of toxicity." - Little Cayman 2004

NOTE Microspathodon chrysurus

 
 
photo array of toxic fishes, possibly also warningly coloured

So,while the representation of fishes in the sorting exercise is by no means complete, the results are still a bit of a surprise, because those fishes known to have toxic flesh (puffer) or have toxic spines (scorpion and surgeon), are rather muted in colour (Left panel). In comparison, other fishes not known to be toxic (although some of them, such as triggerfishes and filefishes have rather sharp dorsal spines - see Right panel) are quite colorful.

These observations may just be reinforcing the point that evolutionary selection for colour in reef-fishes has in many cases been for reasons other than warning of toxicity. Still, let's take a closer look at other examples of Caribbean reef fishes that are toxic and have warning colours, and others that seem to be toxic, but don't have warning colours (at least to our eyes).

photos of Caribbean fishes not known to be warningly coloured
Well, these species certainly have toxicity in the form of venomous flesh and spines, but are they warningly coloured? The only one with conspicuous coloration is the scorpionfish (middle), with its bright pectoral fins that it flashes when disturbed (see photo a few panels below) For several of these non-toxic but highly colorful Caribbean reef fishes, we suspect that their colours have evolved for such "non-defense" reasons such as social (neon goby: a cleaner), territorial (stoplight parrotfish & bluehead wrasse), and mimicry (butterflyfish: simulated eye)
 
 
photograph of a blue tang photograph of an ocean surgeonfish Acanthurus bahianus to show caudal spine
Blue tangs Acanthurus coeruleus have their sharp caudal spines highlighted in yellow, a good warning colour because it transmits well through seawater . Note how brightly it contrasts against the black surround 0.6X In comparison, caudal spines in related ocean surgeonfishes Acanthurus bahianus appear to be unhighlighted. Perhaps the blue piping on the fins (less obvious in the blue colour-phases) acts as a kind of warning. Blue also transmits well through seawater 0.4X
photograph of a porcupinefish photograph of a lionfish Pterois volitans
A porcupinefishe Diodon hystrix is a type of pufferfish and, while it is not known if its tissues are toxic, it can inflate and erect defensive spines. It seems blandly coloured to our eyes, but other relatives may be quite distinctively coloured (puffer, burr, and balloon) 0.2X. The skin, liver, and gonads of pufferfishes contain tetrodotoxins - potent neurotoxins that produce numbness, tingling, respiratory distress, and sometimes death, when consumed. Photoraph courtesy Anne Dupont, Florida. Lionfishes Pterois volitans have venomous spines, warning coloration, and a flamboyant graceful style as they move slowly and sedately about the reef 0.3X. Lionfishes were introduced into the Caribbean almost 3 decades ago, probably from unthinking home-aquarists, and now are quite widely distributed. They are excellent examples of fishes in which toxicity, warning coloration, and behaviour are combined in overall defense. However, their appearance in the Caribbean is cause for great concern
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of scorpionfish lying camouflaged in seaweeds

"There's a scorpionfish hiding in the weeds...let's try to sneak up on it. Easy, isn't it? Scorpionfishes are so confident in their toxicity and their camouflage, that they don't mind any but the most in-your-face confrontation." - Little Cayman 2003

NOTE spotted scorpionfish Scorpaena plumieri

 
 

photograph of a scorpiofish Scorpaena plumieri
Evolutionary selection for overall colour pattern in scorpionfishes, which have venomous spines, seems to have favoured camouflaging benefits over warning-colour benefits. It is more advantageous for the scorpionfish to lie hidden from its prey for greater success in ambushing them. When disturbed, however, the fish displays brightly coloured pectoral fins presumably to warn of its deadly toxic spines.

 

 

 

Spotted scorpionfish Scorpaena plumieri
displaying colorful pectoral fins 0.25X

 

photograph of a splendid toadfish courtesy Anne Dupont, Florida
Toadfishes also bear venomous spines and advertise themselves warningly by the presence of bright yellow and black pectoral fins, and by conspicuous yellow borders on the other fiins. The zebra-striping may camouflage the toadfish's head as it peers out from its usual crevice of overhanging hiding spots. Photograph courtesy Anne Dupont, Florida.

 

 

 

 

 

 

Splendid toadfish Sanopus
splendidus
1.5X

  CONCLUSION: there is no "conclusion" regarding warning coloration in fishes. While there are some good examples, as shown here for scorpionfishes and toadfishes, competing evolutionary "needs" have "clouded" the issue. A logical continuation of the topic would probably be mimicry at COLOURS: FUNCTION OF COLOURS: DEFENSE: MIMICRY.
 
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