Reading 51


The following passage is adapted from an article about reef fish (© 2005 by Les Kaufman).

  1. Gaze at the vivid yellows,
  2. blues, and psychedelic
  3. swirls of a single emperor
  4. angelfish and you’ll sense
  5. the whimsy of evolution.
  6. Go on to explore its home
  7. in lush coral reefs and you’ll
  8. soon hit sensory overload,
  9. assaulted by colors and
  10. patterns that range from
  11. sublime to garish. Coral
  12. reefs are unquestionably
  13. the world’s most colorful
  14. places. But why?
  15. Scientists have long known
  16. that color plays a role in
  17. natural selection and
  18. warning of danger. But
  19. only in the past decade or
  20. so have we begun to
  21. understand how
  22. wavelengths of light (and
  23. therefore color) appear at
  24. different depths and how
  25. various marine creatures’
  26. eyes perceive this light
  27. and see each other—far
  28. differently than humans
  29. see them. Beyond the
  30. world’s reefs, where waters
  31. are turbid or murky, most
  32. creatures use nonvisual
  33. means of communication
  34. such as smell, taste, touch,
  35. and sound. But in the clear
  36. waters of coral reefs, light
  37. abounds, vision
  38. predominates, and animals
  39. drape themselves in blazing
  40. color not only to entice
  41. mates or threaten foes but
  42. also to evade predators,
  43. catch prey, even hide in
  44. plain sight.
  45. Without the artificial light
  46. of a camera, the reef is a
  47. different world. Pale blues,
  48. greens, and yellows abound.
  49. Red is no longer visible, its
  50. longer wavelengths absorbed
  51. by water molecules and
  52. debris. Red pigments on
  53. marine animals may simply
  54. function as gray or black at
  55. depth; why they even have a
  56. red pigment we don’t know.
  57. But we are beginning to
  58. understand more about the
  59. yellows and blues that so
  60. dominate the wardrobe of
  61. reef fish—and help make
  62. them prized targets of
  63. collectors.
  64. Justin Marshall of the
  65. University of Queensland
  66. and George Losey of the
  67. University of Hawaii study
  68. fish eyes. Using a technique
  69. called microspectrophotometry,
  70. they’ve analyzed the visual
  71. pigments and photo-sensitivity
  72. of various reef-fish eyes to
  73. determine how and what fish
  74. see. They’ve also measured
  75. the wavelengths of light
  76. reflected off reef features to
  77. calculate an “average reef
  78. color.” It turns out that in
  79. natural light the yellows and
  80. blues that adorn many
  81. damselfish, wrasses, and
  82. angelfish blend well with
  83. that average reef background,
  84. providing camouflage from
  85. predators.
  86. Brightly colored fish hide in
  87. plain sight throughout
  88. Indonesia, home to the
  89. highest marine diversity on
  90. Earth. In a tiny spot just 
  91. southeast of Sulawesi, clouds
  92. of colored fish swim against
  93. collage of vivid invertebrates
  94. encrusting the reef. With such
  95. an excess of pattern and color,
  96. no one creature stands out.
  97. Up close, regal angelfish flash
  98. eye-popping bands of yellow,
  99. violet, and white. But recent
  100. studies show that as regals
  101. swim against the reef’s
  102. visually complex background,
  103. their contrasting lines merge
  104. in a predator’s brain.
  105. According to marine biologist
  106. Gil Rosenthal, as a reef fish
  107. retreats, distance and motion
  108. can make it difficult for
  109. predators to perceive fine
  110. details and distinguish closely
  111. spaced outlines of contrasting
  112. colors. So at a distance, spots
  113. and stripes blur together,
  114. helping even stationary fish
  115. merge into the background of
  116. the reef and the ocean beyond.
  117. Useful in deception, color can
  118. also speak the language of
  119. love for reef creatures. But
  120. it’s a quick chat. Rising
  121. through a cloud of flasher
  122. wrasses, the males shoot
  123. neon blue stripes across their
  124. bodies. Spurred by a male’s
  125. display of lights, a female
  126. rises in the water column
  127. with her suitor. Job done,
  128. the male instantly goes drab,
  129. and the pair speeds to the
  130. safety of the reef. That
  131. moment exposed them to
  132. great risk from predators,
  133. so the ability to turn off
  134. color was just as important
  135. as the ability to turn it on.
  136. The mechanism for this
  137. quick-change act is a class
  138. of skin cells called
  139. chromatophores. Controlled
  140. by both neurons and
  141. hormones, chromatophores
  142. create the appearance of
  143. color or pattern through
  144. pigments and light
  145. manipulation. Specialized
  146. chromatophores called
  147. leucophores render skin
  148. pale. To produce blue and
  149. iridescent colors like those
  150. used by the flasher wrasse,
  151. iridophores manipulate
  152. crystals of guanine, a common
  153. metabolic waste product, to
  154. scatter white light and then
  155. reflect specific wavelengths
  156. as needed. Such cells can
  157. instantly brand their bearers
  158. as terrifying, invisible, or
  159. irresistible.