Coloration of 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, 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: sighting by predators made easy

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a Pedersen shrimp taken from a video

"Look at how brightly these little Pedersen shrimps stand out! It seems counter-intuitive that selection would favour colour-patterns that a predator could spot more easily, but it would be hard for a fish NOT to notice something so obvious." - Little Cayman Island 2002

NOTE Periclimenes pedersoni


photograph of cleaner gobies at their cleaning stationphotograph of a cleaner shrimp at its station
At least to our eyes, cleaner fishes and cleaner crustaceans tend to be brightly coloured. This is thought to be adaptive, in that host fishes can more readily spot the cleaners against the variegated background of the reef. Although this makes the cleaners easier to spot by carnivorous reef fishes, in this case the predators are not looking for a meal but, rather, are looking to be cleaned. Actual predators of cleaner fishes or cleaner crustaceans seem to be non-existent.

Cleaner gobies Gobiosoma genie 1.5X


Spotted cleaner shrimp
Periclimenes yucatanicus


photograph of cleaner shrimp with moray in Australia
In fact, it's not just that cleaner fishes are not attacked by hungry predators, but recent studies at Lizard Island Laboratory, Australia show that the very presence of cleaner gobies tends to reduce aggressive tendencies of attendant predatory fishes at the station. As hungry as the predators may be, the ministrations of the cleaners tends to reduce their aggression towards other fishes that are hanging around the station awaiting their turn. In fact, the more tactile stimulation given to the piscivorous client fish by the cleaner, the less the client fish chases the attendant bystander fishes. Cheney et al. 2008 Behav Ecol 19: 1063.




A nicely behaving yellow-margined moray
Gymnothorax flavimarginatus being tended
to by an unidentified Indo-Pacific cleaner shrimp 1X


photograph of squat anemone shrimp with anemone
Just as for cleaner fishes, the primary function of bright colours of cleaner shrimps is thought to be for photograph of spotted cleaner shrimp Periclimenes yucatanicus with anemone hostease of identificationn by client fishes who wish to be cleaned. However, could the colours have a secondary function in attracting the shrimps' own predators, if any exist, into lethal contact with the stinging cells of their hosts?

Squat anemone-shrimp Thor ambinensis in
a giant anemone Condylactis gigantea 2X


Spotted cleaner-shrimp Periclimenes
with its host anemone
Condylactis gigantea 2.5X


photograph of a clownfish Amphiprion in its anemone hostIndo-Pacific clownfishes are not cleaners, nor do they live in the Caribbean region, but they too are brightly coloured and live in association with sea anemones. Do their bright colours function to attract predators to their death in the clownfish's host anemone? Alternatively, are their colours a warning to potential predators that they risk being stung by the anemone if they attack the clownfish?

NOTE clownfishes are able to live in sea anemones because of their protective mucous coatings, but it is not known how prawns similarly cope. Clownfish mucus is thicker on fishes that inhabit anemones, and contains substances that may act as a "chemical cloak" (molecular mimicry), or interfere with discharge of the anemone's nematocysts

NOTE the symbiotic relationship between the fish and anemone is continually being investigated. Provision of food scraps to the host may be one benefit, and fecal and urinary wastes are thought also to contribute to the host's nutrition. Recently, another benefit to the anemone has been proposed. This idea originated when clownfishes were seen to be moving actively around and within their hosts at night, whipping their tails about and raising the hosts' tentacles as though to ventilate them. Indeed, oxygen levels tend to be quite low at night, and tests show that the fishes' antics raise the oxygen consumption of the anemones significantly through the night. Yet other data suggest that the presence of Amphiprion benefits a host anemone by increasing its growth and asexual reproduction (by fission), and its survival (Holbrook & Schmitt 2005 Coral Reefs 24: 67).

Clownfish Amphiprion chrysopterus in host anemone 1.5X

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