Gaze at the vivid yellows, blues¹, and psychedelic（引起幻觉的） swirls² of a single emperor angelfish（神仙鱼） and you'll sense the whimsy³（怪念头，反复无常） of evolution. Go on to explore its home in lush coral reefs and you'll soon hit sensory⁴ overload⁵, assaulted by colors and patterns that range from sublime⁶ to garish⁷. Coral reefs are unquestionably the world's most colorful places. But why?  

 

For reasons known only to nature, color explodes across coral reefs, making them Earth's most vivid landscapes. Here in the shallows of a Fijian reef, brilliant soft corals wave in reds, pinks, and yellows as schools of fairy basslets FLASH orange and violet hues⁹. The basslets' different colors aid in species identification, mate recognition, and even camouflage¹⁰ as individuals mass against the kaleidoscope（万花筒） of the reef. What humans see lighted by a photographer's bright strobe may look altogether different in natural light through the eyes of reef creatures. Scientists are now beginning to learn how wavelengths¹¹ of light (and therefore color) change through water at different distances, and—more important—how fish see colors and what messages they might communicate.

 

Bold horizontal bands of black, white, and yellow pop out on a well-lighted sweetlips (Plectorhinchus polytaenia) in Indonesia. The pattern and colors actually help distort the fish's outline when seen in natural light at a distance through water, helping¹² the animal disappear from the view of potential predators¹⁴. Nearby, a neon cleaner wrasse also wears stark¹⁵ stripes. These little fish eat parasites¹⁶ off the flesh and mouths of other fish. The wrasse's stripes may signal that it is a useful helper rather than a ready meal. Neon wrasses vary in coloration geographically¹⁷. A yellow cast near the head (as shown here) indicates an Indonesian species; in Fiji many neon wrasses have a yellow blaze near the tail.

 

The Pacific blue tang (Paracanthurus hepatus)—also known as the artist's pallette surgeonfish due to the shape of the dark patch on its body—was immortalized by the character Dory in the film Finding Nemo. Unlike that benignly¹⁸ daft creature, this real-life surgeonfish in Indonesia carries a sharp retractable¹⁹ blade of bone near the base of its tail. The tail's yellow blaze gives potential foes²⁰ fair warning: Armed and dangerous.

 

A leaf scorpionfish (Taenianotus triacanthus) scouts²¹ for errant fairy basslets in Fijian waters. This ambush²² predator¹³ can change its color to blend with its surroundings. It then lies still, waiting for prey²³ to pass by. "We saw this fish pounce²⁴ a couple of times," says photographer Tim Laman. "His mouth shot out and back in a fraction of a second."

 

A crescent-tailed bigeye (Priacanthus hamrur) seems to wear its emotions on its sleeve—or on its whole body. This sequence of three frames of the same fish shows how it can change from largely silver to striped to solid orange-red, a transformation²⁵ that occurs in a matter of seconds. Pigment²⁶ cells in its skin, called chromatophores, allow it to change color, but scientists don't yet know what each color pattern signifies. Sometimes a sudden shift in color can be used to startle potential predators or threaten intruders. Red light dissipates beyond about 30 feet (10 meters), so the reddish hue⁸ of this fish would appear black in deeper waters, allowing some degree of invisibility for this nocturnal hunter.

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