Reefs
The following passage is adapted from an article about reef fish (© 2005 by Les Kaufman).
- Gaze at the vivid yellows,
- blues, and psychedelic
- swirls of a single emperor
- angelfish and you’ll sense
- the whimsy of evolution.
- Go on to explore its home
- in lush coral reefs and you’ll
- soon hit sensory overload,
- assaulted by colors and
- patterns that range from
- sublime to garish. Coral
- reefs are unquestionably
- the world’s most colorful
- places. But why?
- Scientists have long known
- that color plays a role in
- natural selection and
- warning of danger. But
- only in the past decade or
- so have we begun to
- understand how
- wavelengths of light (and
- therefore color) appear at
- different depths and how
- various marine creatures’
- eyes perceive this light
- and see each other—far
- differently than humans
- see them. Beyond the
- world’s reefs, where waters
- are turbid or murky, most
- creatures use nonvisual
- means of communication
- such as smell, taste, touch,
- and sound. But in the clear
- waters of coral reefs, light
- abounds, vision
- predominates, and animals
- drape themselves in blazing
- color not only to entice
- mates or threaten foes but
- also to evade predators,
- catch prey, even hide in
- plain sight.
- Without the artificial light
- of a camera, the reef is a
- different world. Pale blues,
- greens, and yellows abound.
- Red is no longer visible, its
- longer wavelengths absorbed
- by water molecules and
- debris. Red pigments on
- marine animals may simply
- function as gray or black at
- depth; why they even have a
- red pigment we don’t know.
- But we are beginning to
- understand more about the
- yellows and blues that so
- dominate the wardrobe of
- reef fish—and help make
- them prized targets of
- collectors.
- Justin Marshall of the
- University of Queensland
- and George Losey of the
- University of Hawaii study
- fish eyes. Using a technique
- called microspectrophotometry,
- they’ve analyzed the visual
- pigments and photo-sensitivity
- of various reef-fish eyes to
- determine how and what fish
- see. They’ve also measured
- the wavelengths of light
- reflected off reef features to
- calculate an “average reef
- color.” It turns out that in
- natural light the yellows and
- blues that adorn many
- damselfish, wrasses, and
- angelfish blend well with
- that average reef background,
- providing camouflage from
- predators.
- Brightly colored fish hide in
- plain sight throughout
- Indonesia, home to the
- highest marine diversity on
- Earth. In a tiny spot just
- southeast of Sulawesi, clouds
- of colored fish swim against
- a collage of vivid invertebrates
- encrusting the reef. With such
- an excess of pattern and color,
- no one creature stands out.
- Up close, regal angelfish flash
- eye-popping bands of yellow,
- violet, and white. But recent
- studies show that as regals
- swim against the reef’s
- visually complex background,
- their contrasting lines merge
- in a predator’s brain.
- According to marine biologist
- Gil Rosenthal, as a reef fish
- retreats, distance and motion
- can make it difficult for
- predators to perceive fine
- details and distinguish closely
- spaced outlines of contrasting
- colors. So at a distance, spots
- and stripes blur together,
- helping even stationary fish
- merge into the background of
- the reef and the ocean beyond.
- Useful in deception, color can
- also speak the language of
- love for reef creatures. But
- it’s a quick chat. Rising
- through a cloud of flasher
- wrasses, the males shoot
- neon blue stripes across their
- bodies. Spurred by a male’s
- display of lights, a female
- rises in the water column
- with her suitor. Job done,
- the male instantly goes drab,
- and the pair speeds to the
- safety of the reef. That
- moment exposed them to
- great risk from predators,
- so the ability to turn off
- color was just as important
- as the ability to turn it on.
- The mechanism for this
- quick-change act is a class
- of skin cells called
- chromatophores. Controlled
- by both neurons and
- hormones, chromatophores
- create the appearance of
- color or pattern through
- pigments and light
- manipulation. Specialized
- chromatophores called
- leucophores render skin
- pale. To produce blue and
- iridescent colors like those
- used by the flasher wrasse,
- iridophores manipulate
- crystals of guanine, a common
- metabolic waste product, to
- scatter white light and then
- reflect specific wavelengths
- as needed. Such cells can
- instantly brand their bearers
- as terrifying, invisible, or
- irresistible.