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07/24/2008
An Odd Old Animal
NOTE posted July 28: Due to the impending site conversion, there
will be no new column this week. The next column will be posted on
Thursday, August 7.
Before finishing and posting this column, I loaded the
dishwasher and used a sponge to clean up the counter top. OK,
you’re right, I’ve also seen the reports that kitchen sponges
harbor all kinds of nasty stuff but I like to think that my sponge
is different. It wouldn’t be the first time I was wrong about the
sponge. To wit, I quote from my 1962 World Book
Encyclopedia: “At one time people thought sponges were plants
because they do not move around as most animals do.” Well,
here it is 2008 and I have to confess that until this week, in my
ignorance, I too thought of the sponge as a plant. Then I read a
brief report, edited by Constance Holden, in the Random
Samples section of the July 4 issue of Science.
Her report deals with the giant barrel sponge, perhaps known to
you as Xestospongia muta. This large sponge has a beer barrel
shape and makes its home in Caribbean coral reefs. Some of
these giant sponges have grown as large as 6 or 7 feet or so in
diameter. Scuba divers sometimes call the sponges “redwoods”
because of their size and presumed age. It was the statement in
the report that these sponges are “the longest lived animal
species extant today” that sent me scurrying to the World Book,
thinking the sponge to be a plant and not an animal.
Aside from its size, what makes the giant barrel sponge so
special? It’s that “longest lived animal” bit. Marine biologists
associated with Joseph Pawlik’s lab at the University of North
Carolina, Wilmington, estimate that a huge sponge that died in
2000 was 2300 years old! If true, those scuba divers were
certainly correct in comparing the giant barrel sponge with
redwoods in California. When one hears these days of the dating
of something old, one immediately thinks of carbon dating or
some other technique involving radioactive isotopes.
Unfortunately, it seems that carbon dating is either difficult or
inapplicable for these sponges. The UNC researchers base their
estimate of age on a study of the growth of these sponges over a
four and a half year period. It’s on the basis of these
observations of the growth rates of sponges that they calculate
the age of 2300 years for the recently deceased giant barrel.
From the standpoint of a completely uninformed observer, me, I
would feel more comfortable about the estimate of 2300 years
based on growth rate observations over a 4-5 year period if there
were some other dating method corroborating the estimate. I did
visit a UNC Web site and found myself, to my surprise, at a point
where it appears I could have gotten the full text of the paper the
researchers published in the journal Marine Biology online. My
surprise was due to the fact that the site had a warning that it was
intended only for faculty and students at UNC and that if I
clicked on the link to the paper I would bear responsibility for
my actions regarding the paper. Hey, I read almost daily about
someone in trouble because of his or her shenanigans on the Web
so I didn’t access the paper.
Even if that sponge lived only a thousand years, what kind of life
was it for him or her? (Actually, a sponge can reproduce
sexually or asexually so it might have been a him-and-her?) It
seems to me that a sponge’s life can’t be very exciting. It doesn’t
have a mouth, doesn’t have a nervous system and doesn’t have
any internal organs. Obviously, it doesn’t have eyes or ears. It’s
either the most or one of the most primitive forms of
multicellular animals on Earth. It’s got all these cells with little
hairs, cilia, that wave around, drawing in bacteria or other bits of
food – apparently, some sponges are even carnivorous, drawing
in small crustaceans.
A sponge begins its life as a single-celled egg, which keeps
dividing until it becomes a larva with cilia to move it around
until it finds a rock or other suitable object on which to attach
itself and grow into a full fledged sponge. There are about 5
thousand different species of sponges and of considerable
practical interest is the nature of the material that makes up their
skeletons. Why? It’s the skeleton of the sponge that we know as
the sponges that we have around the house. Some sponges have
skeletons composed of spicules (little spiky things) of calcium
carbonate while others are composed of spicules of silicon (?),
according to my International Encyclopedia of Science and
Technology.
Aha! Old Bortrum may not have known the sponge was an
animal but a skeleton made of spicules of silicon? I think not.
Sure enough, a visit to an Iowa State University Web site on
Phylum porifera, sponges, not only says there are 9,000 (not
5,000) species of sponges but that sponges are classified by what
makes up their skeletons. One class is based on spicules of
calcium carbonate (OK), another on spicules of silicon dioxide
(now we’re talking sense!). (Sand and quartz are silicon dioxide,
while silicon is elemental silicon, of the ubiquitous silicon chip.)
But I have digressed, in a shameless display of self redemption.
What about the third class of sponges, the skeletons of which
we’ve all used at one time or another? The skeletons of these
sponges are made of horny, elastic protein fibers known as
spongin. These fibers like to pick up water and their elasticity is
well demonstrated by the number of times you can squeeze out
your sponges before they die, which is never in my experience.
If your sponge is not synthetic, it could be that it was harvested
from the sea on a fishing boat, laid out on deck until the flesh
decayed, then beaten to remove the decayed flesh and other hard
stuff, leaving the soft skeleton behind to be hung up and dried.
According to the World Book, some sponges are also capable of
impressive feats of regeneration, replacing parts of the body cut
off. Some sponges can even be passed through fine cloth, like a
sieve, and the cells separated into individual cells or groups of
cells. When put back in water the cells amble around and can
form a new sponge.
All in all, the sponge is a strange animal indeed. I had planned to
write about another strange animal, the platypus, but maybe next
time.
Allen F. Bortrum
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