Journey North Teacher's Manual

Bountiful Barnacles If you've ever been to a seashore or an ocean harbor, you've probably seen or heard about barnacles. These small shell-like creatures attach themselves in dense clusters underwater to the bottoms of boats, to dock posts and pilings, and to shoreline rocks and other submerged surfaces. Barnacles live only in marine or salt water environments. They live on hard surfaces at all latitudes at all depths from the intertidal zone to the deep sea. (Barnacles in the intertidal region spend part of their day, during low tide, without seawater around them.)

Barnacles also can "hitch a ride" and attach themselves to living things. They hitchhike on turtles and several species of whales, where they are known to travel for years at a time. Some barnacles try to latch on to other cetaceans, like dolphins. They also try to attach to marine mammals like manatees. How do they do it?

Sticking Tight Barnacle larva swim along in the ocean until they are ready to "stick" around. Then they secrete a glue-like substance and attach themselves head-first. The "glue" is so strong that even after the barnacle dies, its base may remain long afterwards. Dentists are even studying this "glue" because of its ability to stick so tight!

Barnacle Basics Barnacles may look like clams (mollusks) but they are actually crustaceans, related to lobsters, shrimp and crabs. Indeed, most barnacles have hard calcareous plates that protect their body. The hard "shell" is actually a calcium-based series of plates. Six plates form a circle around the crustacean, and four more act as a door that the animal can open or close. If you have ever observed a barnacle in the water, you might have seen it emerge from its shell.

Barnacles Off and On Barnacles living on whales, turtles, manatees and other creatures stay on for different lengths of time. It depends on several factors. Gray Whale expert Dave Rugh from National Marine Mammal Laboratory in Seattle, WA, says slower whales (like gray whales) have more barnacles than fast cetaceans (like dolphins). Gray whales migrating south have only large barnacles, while those migrating north have both large and small, indicating that the barnacles attach to the whales in winter. It also indicates that the barnacles survive for one or more years on a whale, in spite of skin sloughage. Some species of barnacles, such as those that attach to humpback whales, live only one year anyway. Barnacles may also be killed or knocked off as their host enters fresh water, breaches, or rubs against objects -- such as another whale -- so the attachment is not an indefinite thing. However, for whales, the barnacle's penetration is deep enough to leave scars that last 10-20 or more years. A barnacle on a whale pulls the skin into the cavity of its shell, making an attachment that penetrates beyond the layer of sloughing skin.

In the case of manatees, Save the Manatee Club indicates that the manatee's process of skin sloughing helps manatee skin to stay relatively free of barnacles. And the fact that manatees regularly return to fresh water may also discourage barnacles from attaching too, since barnacles live only in marine or salt water environments. Also, the manatee's skin is suprisingly hard. Some say it feels like corkboard on bulletin boards, except wet; others say it feels like the covering of a basket ball.

• Take a look at these whale and manatee video clips. Pay close attention to their skin. What do you notice? Does one have more barnacles? Which one? Since both are marine mammals, what reason(s) might explain the differences?

  Compare the skin of a manatee ...	and a gray whale.
  Video Clip: Barnacles on Manatee. Watch It Now (Viewing tips) Credit: Keith Clements	Video Clip: Barnacles on Gray Whale. Watch It Now (Viewing tips) Photo: Keith Jones

• Whale biologists look at the pattern of barnacle clusters in order to tell individual grays apart. This is possible because no two barnacle clusters are alike! Give it a try yourself. Dr. William Megill gives you step-by-step help, with lots of photos for practice! Lesson: Who is That Whale? Gray Whale Photo ID Matching
• Manatees can't stay in salt water all the time, because they require freshwater to live. It is likely that these periodic returns to salt water make life on manatee's skin a rather inhospitable habitat for barnacles. Video and discussion: Salinity of Manatee Habitats Changes with the Seasons

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