Coloration in reef organisms
 
column spacer Coloration in reef organisms
 
  hot buttons for colours section of Biology of Caribbean Coral Reefs website
This section continues the topic of how colours are created. Topics of HOW COLOURS ARE PERCEIVED and the FUNCTION OF COLOURS can be accessed via the icons.
 
 

How colours are created

 

Colours in marine animals are created by structural elements, considered here, and by PIGMENT DEPOSITS, by CHROMATOPHORES, and by the PRESENCE OF OTHER ORGANISMS.

NOTE: this generally involves refraction (bending) of light or diffraction (differential reflection) of light. Common examples are rainbows, and most natural blue colours, such as in butterflies, coral-reef fishes, and birds

 
 

How colours are created: structural elements

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a queen angelfish taken from a video

"Wow! Is there anything more gaudy than a queen-angelfish's colours? The blue colour is not from a pigment but, rather, from differential refraction of light from deep within the fish's skin...the light bounces around...and...out...comes...gaudyness!" - Turks & Caicos 2005

NOTE Holacanthus ciliaris

 
 

illustration of how blue colours are created in a fish
Blue colours in fishes, such as this queen angelfish Holacanthus ciliaris, are produced structurally through diffraction of light as it penetrates to varying depths into a layer of reflecting iridiphores. The light bounces around within the tissue until eventually emitted as blue wavelengths.

NOTE a type of chromatophore containing a white, reflective pigment

 

illustration showing how green colours are produced in a fish
What about green colours, as in this stoplight parrotfish Sparisoma viride? These result from the passage of these same blue wavelengths as they exit the skin through a layer of yellow chromatophores.

 

 

 

 

 

 

 

 

Blue plus yellow equals green

 

illustration showing how purple colours are produced in a fish
Similarly, purple colours in fishes result from the transit of blue wavelengths through a red layer of chromatophores. Yellow colours are produced by reflection from yellow chromatophores. Colours in fishes, then, can result from a combination of chromatophores, pigment deposits, and structural effects on wavelengths.

 

 

 

 

Purple and yellow colours predominate in the fairy basslet Gramma loreto 0.5X
Note that structurally produced blue wavelengths are changed to purple as they pass
upwards through red chromatophores sited in a more shallow part of the dermis layer

 

photograph of a beaugregory damselfish
As might be surmised from the array of colours seen in coral-reef fishes, their visual acuity and ability to perceive colour are good. Beaugregory damselfishes Stegastes leucostictus, for example, are thought to be able to distinguish some 50 species of fishes in territorial encounters.

NOTE other characteristics such as scent, vibrations, and behaviour are certainly also involved

 

Beaugregory damselfish Stegastes leucostictus 0.5X

 
 

photograph of shell lining of red abalone Haliotis rufescens
The iridescent colours in the mother-of-pearl layer of pearl oysters results from diffraction of light from the hard nacre layer lining the inside of the shell. Note that photograph of mother-of-pearl lining of a wing oyster Pteria penquinneither of the shells shown here is from the Caribbean, but both provide good examples of mother-of-pearl.

NOTE a French word meaning "mother-of-pearl"

California red abalone
Haliotis rufescens 0.6X


Indo-Pacific wing oyster
Pteria penguin 0.6X

 

  drawing to show how nacre is formed by a mollusc
Nacre is comprised of many overlapping layers of calcium carbonate laid down within a protein framework. The materials are secreted by the mantle, the soft tissue of the body that lies adjacent to the shell.
  drawing showing how colours are emitted from nacre
As light shines into the layers of nacre, it penetrates to different depths and is broken up or diffracted, then re-emitted in its spectral components. Not all the wavelengths are re-emitted, however. Different wavelengths have different energy levels. Some bounce sideways and are absorbed by the shell, and others combine to form different hues.
 
photograph of nacre of red abalone Haliotis rufescens

With changing angle of view the diffraction effects change; hence, producing iridescence
photograph of nacre of red abalone Haliotis rufescesens1
 
double-headed arrow
 
 

photograph of 2 strings of natural pearls
Pearls are formed in bivalve molluscs through deposition of nacre to coat irritants that find their way between the shell and mantle tissue. For example, sand grains are commonly the bases for natural pearls. A pearl's colour derives from the colour of the nacre, and its lustre from the depth and number of layers of nacre photograph of pearl-oyster with cultured pearls courtesy Krikor Tersakiadeposited. The more layers, the deeper and richer is the lustre. Cultured pearls are formed around starter objects such as spherical plastic beads or bits of natural shell that are inserted into the oyster. The less time the oyster is allowed to grow after insertion of such an object, the poorer will be the quality of the pearl.

Natural pearls from freshwater bivalves are
typically irregularly shaped with good lustre

 

These 2 perfectly spherical cultured pearls in the pearl oyster
Pinctada
sp. have poor lustre because of the large-sized plastic
spheres inserted starters. Photograph courtesy Krikor Tersaki, Japan.

 
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