Nano Gobies

species of Acropora. Acroporids made their evolutionary
appearance about 35 million years ago, and if some of
the early species had the tendency to fragment, it is possible,
albeit unlikely, that some of the early genomes are
still with us, in a manner analogous to bdelloid rotifers.
Each individual fragment of the clone might only live
a few years, but clonal offspring could be around for a
long, long time.
It has been said many times by many biologists, including
the one writing this article, that at least some
corals may have the unrealized potential to live forever,
but obviously that is not necessarily true. Recent work
has shown that individual polyps may be subject to senescence
in Madracis mirabilis, and that, while the colony
may live a long time, any given polyp
may live no longer than a decade or two.
Thus, in colonial corals, while the whole
colony may live much longer, the polyps
comprising it may be replaced regularly.
Polyp replacement has not been investigated
in other corals, leaving a lot of
unanswered questions. For example, is
this property found only in zooxanthellate
corals? Or is it found only in certain
evolutionary lineages of colonial corals?
Recall that there are two main groups of
stony corals, the robust and the complex
lineages; colonial corals are found
within each group, but the dynamics of
polyp formation and replacement have
not been compared either within or between
them.
Do all colonies replace polyps? If so,
does the manner of polyp replacement
have a bearing on longevity? If not, is
the presence or absence of replacement
correlated in any way to life span? And if
polyps are replaced in all/some colonial
corals, what happens in solitary corals?
Is there, for example, some inherent factor
that limits the ages of coral polyps
and, by inference, solitary corals? And
what about the non-scleractinians?
Obviously, corals probably don’t live
forever; but some of them may live a
very long time, indeed. The growth rates
of corals given in this article vary over
a factor of 6,250, from about 4 μm/
year to about 25,000 μm/year; if these
growth rates were all assumed to be linear
extensions, then in a million years
these rates would give length extensions
of 13 feet (4 m) to 15.5 miles (25 km)
for corals at each of these extremes.
While a coral growing 15 miles in length
seems very unlikely, a coral growing 13
FIRST
feet seems entirely possible. And what about a coral that
breaks frequently? Could the cumulative linear growth
of all of the “offspring” from one branch be miles in
length after a million years of fragging? I certainly think
it is possible, even likely. And then there is the question
of how old some of the biggest of the very slow-growing
deep-sea corals are. The number of individual corals
from the deep sea whose ages have been determined and
published is far less than 100. Who knows what awaits a
diligent researcher curious about coral ages?
REFERENCES:
http://www.coralmagazine-us.com/content/elders-referencesage-corals
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