Published April 2005
Dear Sea Scoop!,
I noticed, while snorkeling in Maui, Hawaii, that some fish had brilliant colors of yellow – while others were a bit more camouflaged. I wonder – wouldn't this bright yellow color be a poor evolutionary choice as far as predator protection? How do tropical fish colors act as protectors to enemies?
You are correct that bright colors often attract predators. Most reef animals are masters of disguise because their life, indeed, depends on it. Fish try to blend into the background of the reef not only with muted colors, but also with different types of coloration that confuse potential predators. For example, the foureye butterfly fish (Chaetodon capistratus) has a false eyespot near its caudal (tail) fin to misdirect a predator looking for a meal. Some fishes, like the banded butterfly fish (Chaetodon striatus) have "disruptive" coloration, such as vertical stripes running down their body and over their eyes, so they only look like a fish upon close inspection. Other marine animals can grow fleshy appendages and tabs over their bodies to help them look like seaweed or sponges. Many marine animals use a type of camouflage known as "countershading". These animals have a dark dorsal (top) side and a light ventral (bottom) side. When a predator is swimming under them looking up, a countershaded animal blends in to the light color of the water and sky. When a predator is swimming over them looking down, the countershaded animal blends into the murky darkness of the ocean depth. Still other reef animals can change color using their chromatophores (krow-ma-toe-FORES) which are cells filled with pigments (color) stimulated by nerves or hormones.
But let's return to your question about bright yellow color being a poor choice for predator protection. In the world of coral reefs, the only thing more important than avoiding being another fish's dinner, is finding a mate. Many fishes of the coral reef display the brilliant colors that typify reef fishes only for a short time when they are breeding. One must strike a balance between flashy colors to attract a mate, and lying low to avoid predation. For those reef fish that are always brightly colored, current theory suggests their coloration acts as a "no-trespassing" sign to warn other fish of territorial boundaries. One other thing to note is that many reefs are brilliantly colored, so being bright yellow may just help a fish blend into the reef!
Did you know that many reef fish can change sex? These fish are called sequential hermaphrodites and include many parrotfish (Scaridae family), wrasses (Labridae family) and sea bass (Serranidae family). This allows the fish harem to maintain a proper ratio of males and females to assure population maintenance. Most of the sequential hermaphrodites in the Caribbean are protogynous hermaphrodites, meaning they change from female to male. In most cases, there is only one large breeding male per harem, but many born or "initial phase" males and females. When something happens to the breeding, or terminal phase male, the largest female will change sex and become the new terminal phase male. This new terminal phase has the lucky job of breeding with the females in his harem. The terminal phase male is larger than the initial phase females and males and is recognized by its bright coloration.
For more information on coral reef fish:
Coral Realm. New World Publications Marine Life Learning Center
Monterey Bay Aquarium Coral Reef Fish Coloring Page
For more information on sex-change in reef fish:
University of Florida Museum of Natural History
Hermaphroditism: A Tale of Two Sexes
Have a question about the world beneath the waves? Write it down and send it to Sea Scoop! Please remember to include your name and where you're from.
For more information on marine science in the Virgin Islands, visit the University of the Virgin Islands' Center for Marine & Environmental Studies.
Elizabeth Ban is the University of the Virgin Islands Marine Adviser for St. Thomas and St. John. She works to inform and educate citizens about ocean resources and promote coastal ecosystem health. She is based at UVI's Center for Marine and Environmental studies on the St. Thomas Campus. For more information about UVI's Marine Advisory programs, please call 340-693-1392.
Published April 2005