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=='''Coral Coloration'''==
=='''Coral Coloration'''==
===Location===
Depth, sedimentation, etc


===Zooxanthallae===
===Zooxanthallae===

Revision as of 21:54, 15 April 2014

The Role of Color on the Reef

Introduction

Fish vision

Rods and cones

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The way that fish see the world is dramatically different from the way humans see it. This is largely due to the scattering of light that occurs in their underwater habitats. Scattering of light has a huge impact on both underwater visual systems and the colors used in marine signaling systems.[1] The retina of the eye contains light detecting cells called rods and cones. Rods are responsible for detecting low-intensity light while cones pick up high-intensity light and colors. Fish that live closer to the surface, where there is more visible light, tend to have more cones than fish that love in deeper waters and rely more on rods. Those that live below the photic zone often have more rods than cones while those that live in deep-sea habitats often lack cones altogether. Fish that only have one or fewer types of cones are not able to detect different colors. They can only detect variations in light intensity and as a result see shades rather than colors. Fish that live closer to the surface and in more lighted waters, such as the coral reef environment, are capable of seeing a broad array of colors. Their retinas contain two or three different cone cells, giving them an acuity which exceeds that of human vision.[2]

UV visual sensitivity

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It is a common, but certainly not dominant, feature for coral reef fish to possess short wavelength vision.

This allows them to see a broader spectrum of light than other species. There are three categories used to describe this vision: ultraviolet (UV)-sensitive, UV-specialized, and violet-specialized.[3]

UV-Sensitive: This type of fish vision is characterized by a lack of specialized UV receptors. In this case, the UV blockers simply fail to function below 400nm. These fish probably do not have true UV color vision and cannot discriminate between hues. [3]

UV-Specialized: These eyes allow transmission of UV light to the retina. They fail to block some of the light in the UV spectrum. This category of fish vision is characterized by the possession of receptor cells that are responsive to visual pigments absorbed at 360nm. These fish possess UV-sensitive cone cells with peak absorption between 300nm and 400nm. They may have true color vision and recognize UV as a color. [3]

UV-Sensitive Cone Cells: These cells allow for true color vision and hue discrimination. It is likely that they provide the fish with separate perceptual functions, such as prey detection.[3]

Violet-Specialized: Fish with this type of vision are capable of blocking some radiation below 435nm. Their receptor cells are most sensitive to radiation that is between 400nm and 435nm. This allows for increased sensitivity to violet light in deeper water where UV radiation is less than violet radiation and there is a lower risk of ocular damage from harmful UV radiation. These fish display improved color constancy and focusing ability and are able to retain some of the advantages of UV-specialized vision (i.e. prey detection).[3]

Fish Coloration

Specific colors and patterns

blue, red, orange, yellow, green, gray, white, black, brown, silver[4]

brightness

bands, stripes, bars, speckles, spots, lines, blotches, eye markings, ocellated spots

The Role of the Environment in Coloration

Not only does water control the light field at any location within the reef, but it also has a dramatic effect on how the colors and patterns of a target are perceived by the observer.[1]

Roles of Colors

Protection Against Predation: warning colors, camouflage



Mate Selection

Life cycle phases

purpose of color as a juvenile vs. adult[5][6]

specific examples: Queen Angelfish, Schoolmaster, Dusky Damselfish

Polymorphism

Permanent color variations in species (geographical)[7]

Color and marking phases

temporary changes to enhance camouflage, to indicate mood, or for intraspecies communication (courtship)

instantaneous or over a long period of time


Coral Coloration

Zooxanthallae

algae give coral its color


Fluorescent Pigments


[8]

Lighting is one of the most defining factors in determining the color of corals. Intensity, concentration, and wavelength (color), all play a role in how coral expresses its color. The wavelength of light determines how effectively the zoxanthellae can use the light to photosynthesize and produce nutrients for the coral. It's important to have a baseline understanding of ultraviolet light, which is not detectable by the human eye, to fully understand the different types of light the zooxanthellae can utilize.

UV-A: 315-400 nm The upper region of wavelength spectrum can pass through normal silicate glass and exhibits few, if any harmful effects on living tissue.

UV-B: 280-315 nm This range of wavelength is responsible for most sunburns. It can not pass through silicate glass and is usually stopped in a few feet of water. However, in the crystal clear waters of reef areas, these rays can penetrate up to 30m deep.

UV-C: 100-280nm The

Nutrition also plays an important role in how zooxanthellae and coral obtain their vibrant colors. Zooxanthellae have a compensation point at which the rate of photosynthesis equals the rate of cellular respiration. This is the bare minimum amount of return they can get on their photosynthetic processes in order to survive. The main factor in this equation is the amount of light available to the algae. This amount of light can be determined by depth, geographical location, or amount of nutrients in the water. On the opposite side of the spectrum, there is also a saturation point. At this point, an increase in light intensity does not positively affect the amount of metabolic product the zooxanthellae can produce. This saturation point is important because it allows more nutrients to be consumed by the host coral the zooxanthellae reside on. However, corals do not feed solely on the metabolic waste of the zooxanthellae; they also consume phytoplankton and zooplankton in the water. While there is a notable lack of phytoplankton and zooplankton in the majority of coral reef areas, their presence still plays an important role in how the coral maintain their zooxanthellae population. Corals balance the concentration of zooxanthellae on their surfaces based on their other dietary needs. An increase of phytoplankton and zooplankton yields less of a need to sustain the zooxanthellae. In an excess of these microscopic nutrients, corals will actually expel their zooxanthellae, rendering them less colorful, or even colorless (known as bleached.) While this isn’t currently the leader in cause of coral bleaching, it can be detrimental to the ecosystem in many various ways.

Coral Bleaching

Coral bleaching is a detrimental condition that is caused by either the coral's expulsion of its intracellular symbiotic partner, zooxanthellae, or the loss of pigment in this algae. Corals release this algae from its surface when they are subjected to stressful conditions. While there are many factors that can cause the stress of corals, such as exposure to air, solar radiation, and fresh water dilution, the most common reason is rising sea temperatures. [9]As this algae provides the coral with most of its color, once void of the zooxanthellae, the coral becomes a lighter, or even stark white, hence the term, "bleaching." While corals can live for short periods of time without their zooxanthellae partner, the majority of events that result in loss of zooxanthellae also result in death for the corals. Apart from these direct consequences that bleaching events have on the coral themselves, the white environment the bleaching creates can also render the area unsustainable for the otherwise vibrant fish. Fish use the colorful ecosystem to hide predators as well as stalk prey, so the rapid change in color alone can be devastating to a reef.

References

  1. 1.0 1.1 Marshall, N. J., K. Jennings, W. N. McFarland, E. R. Loew, and G. S. Losey. "Visual biology of Hawaiian coral reef fishes. III. Environmental light and an integrated approach to the ecology of reef fish vision." Journal Information 2003, no. 3 (2003).
  2. Sumich, James L. and John F. Morrissey. Introduction to the Biology of Marine Life. Sudbury: Jones and Bartlett Publishers, 2004. Print.
  3. 3.0 3.1 3.2 3.3 3.4 Losey, G. S., W. N. McFarland, E. R. Loew, J. P. Zamzow, P. A. Nelson, and N. J. Marshall. "Visual biology of Hawaiian coral reef fishes. I. Ocular transmission and visual pigments." Journal Information 2003, no. 3 (2003).
  4. Marshall, N. J., K. Jennings, W. N. McFarland, E. R. Loew, and G. S. Losey. "Visual biology of Hawaiian coral reef fishes. II. Colors of Hawaiian coral reef fish." Journal Information 2003, no. 3 (2003).
  5. Longley, W. H. "Studies upon the biological significance of animal coloration. I. The colors and color changes of West Indian reef‐fishes." Journal of Experimental Zoology 23, no. 3 (1917): 533-601.
  6. Cardwell, J. R., and N. R. Liley. "Hormonal control of sex and color change in the stoplight parrotfish,< i> Sparisoma viride." General and comparative endocrinology 81, no. 1 (1991): 7-20.
  7. Messmer, Vanessa, Lynne van Herwerden, Philip L. Munday, and Geoffrey P. Jones. "Phylogeography of colour polymorphism in the coral reef fish Pseudochromis fuscus, from Papua New Guinea and the Great Barrier Reef." Coral Reefs 24, no. 3 (2005): 392-402.
  8. Alieva, Naila O., Karen A. Konzen, Steven F. Field, Ella A. Meleshkevitch, Marguerite E. Hunt, Victor Beltran-Ramirez, David J. Miller, Jörg Wiedenmann, Anya Salih, and Mikhail V. Matz. "Diversity and evolution of coral fluorescent proteins." PLoS one 3, no. 7 (2008): e2680.
  9. Buchheim, Jason. "Coral Reef Bleaching." Coral Reef Bleaching. N.p., 1 Jan. 1998. Web. 16 Apr. 2014. <http://www.marinebiology.org/coralbleaching.htm>.
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