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, 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: other: UV protection

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of an indigo-hamlet taken from a video

"Here's a nice dark-blue indigo-hamlet having fun in the sun. I wonder if coloration in reef organisms has any sort of role in protection from ultraviolet light? Or, maybe the harmful rays are absorbed too quickly in the water for them to give anyone a sunburn..." - 2002 Turneffe Island. Video courtesy Andy Stockbridge, Belize.

NOTE Hypoplectrus indigo


diagram showing how pigment granules in the skin of a coral polyp shield the underlying symbionts from harmful wavelengths
In fact, UV irradiation does penetrate the ocean and, while its energy attenuates quickly with depth, it is known to affect photosynthesis in corals at depths of up to 20m and to cause bleaching in seaweeds at shallower depths. Pigments in corals that generally shade out light may also shade out harmful UV irradiance. In the accompanying diagram, pigment granules in the epidermis are blocking penetration of sunlight to the deeper gastrodermal layers where the photosynthesising symbionts are housed.

NOTE bleaching in corals is a different phenomenon, involving expulsion and/or death of the photosynthesising symbionts. Loss of symbionts causes whitening of the corals and, if long-lasting, can be life-threatening. See CORALS: A CASE STUDY: CORAL BLEACHING


photograph of a school of silversides in shallow water
Reflective scales in pelagic fishes are thought to be mainly for camouflage, but their mirror-like properties could also provide protection from UV light.





Schools of silversides like herring and anchovies
feed by filtering food from the plankton; hence,
are found commonly in shallow surface waters 0.25X


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