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.)
covering the bottom of a buoy
Click image to enlarge
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?
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!
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.
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.
This! Video Study, Photo Study
- 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
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
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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