Reading 51

Reefs

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. a 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.