Nano Gobies

the same genome is likely present, and both the genome
and the asexually reproducing individual could have the
same immense age.
Scientists who study corals recognize two major lineages
of scleractinian corals: “robust” corals and “complex”
corals. Although it is too much of a simplification
to say that all robust corals, such as Porites, form massive
colonies and all complex corals, such as acroporids, form
branching colonies, there is a trend that way. Tropical
reef corals generally have the capability to reproduce
asexually by fragmentation, but this is much more prevalent
in the branching corals. Probably the best example
of this would be a shallow-water Indo-Pacific Acropora
thicket or the “used-to-be” Acropora cervicornis meadows
in the Caribbean. Every time a reef-pounding storm
blew through, the coral fragmented and started anew.
This was natural coral fragging on a huge scale; but how
old is any piece of that mass of fragments? The genome
that was in the original founder polyp might conceivably
be centuries old, but it would be very hard to find it and
confirm that, although if the original attachment skeleton
was still present, radiometric means would be capable
of determining it. The original coral may be either
long, long, long dead or very much alive. But the coral’s
genome lives on in a lot of places. A question one might
ask is, “Once established, how long does the genome in
one of these coral thickets live?” I suspect the answer
will be: “Until global climate change wipes out the whole
clonal population.”
Porites lobata, one of several
massive, mounding species in a
genus whose oldest known member
has been found to be more than
1,000 years of age.
COUNTING THE CANDLES ON THE CORAL
CAKE
How can the age of a coral be determined? This is where
the nitty of the coral “type” meets the gritty of age. The
ages of different coral types have to be determined differently,
and as such are not strictly
comparable. Many scleractinians,
particularly the massive
forms, such as Porites, deposit
their skeletons continuously in
a manner analogous to the way tree rings are formed.
The polyp sits in the skeletal cup, or corallite, and secretes
new skeleton at the interface between the coral’s
epidermis and the adjacent skeleton. Skeletal density
varies depending on the available light and the temperature,
and these physical factors, in turn, vary in a
predictable manner thoughout the year. As a result, just
like tree rings, the skeleton produced by a massive coral
shows growth banding.
At the other extreme of the animals called “corals”
is the black coral, whose skeleton is wholly a hardened
proteinaceous material. These animals may deposit yearly
growth rings or increments, but they are usually too
small to measure, particularly in slowly growing individuals.
However, as they grow, these animals incorporate
carbon isotopes in their skeletons, and with careful sampling
the differences in the isotope ratios can be used to
determine age by radiometric means.
Finally, some of the octocorals, such as gorgonians
and sea pens, have an internal skeleton containing sizable
amounts of both protein and calcium carbonate.
PETER ISDALE/AIMS
76 CORAL