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Gorgonians are corals in the subclass Octocorallia
and the order Alcyonacea. They are divided into
two main groups, the highly varied Scleraxonia
and the suborder Holaxonia. The Scleraxonia
group has an inner axis composed of dense or
fused skeletal elements, the sclerites. These
sclerites are also found in soft corals, but
rarely form solid axes there. In contrast, the
Holaxonia has a flexible axis, made of a protein
called gorgonin. Both groups contain branched
and fan-like colonies of polyps, but only the
Scleraxonia has encrusting forms.
in all tropical reef systems may, like other
corals, be either zooxanthellate or azooxanthellate,
having or lacking photosynthetic symbiotic dinoflagellates,
respectively. In shallow reefs of the tropical
western Atlantic, zooxanthellate forms are dominant
and are often abundant reef components. Although
gorgonians are common in the wider Indo-Pacific
and Red Sea, especially on reef slopes, shallow
reefs are usually devoid of anywhere near the
number of gorgonians found in the Atlantic.
As is true of most coral taxa, diversity in
the Pacific is much greater than in the Atlantic,
although there are proportionately fewer zooxanthellate
species. Colors, as well, tend to be bright
to shockingly gaudy in the Pacific, with uniform
purple-greys and reds being most common in the
Unfortunately, for the aquarist, the gorgonians
of the Pacific are generally very difficult
to keep alive in tanks. There are a few zooxanthellate
species that can be expected to survive relatively
well. The more desirable species, though, such
as some of the bright seafans and brilliant
blue arborescent colonies, are usually doomed
to a short lifespan in captivity. It is likely
that a lack of adequate foods is to blame. In
contrast, Caribbean species, particularly those
commonly collected, are mostly photosynthetic
and tend to fare well in captivity. There are
exceptions; commonly collected are the orange
and red tree gorgonians, Diodogorgia nodilifera
and some look-alikes, and the orange tree gorgonian,
Swiftia exerta, which lack zooxanthellae
and share similarly dismal success in most aquaria
with their aposymbiotic Pacific brethren. There
are many gorgonians in both oceans which are
variably common but are rarely or ever intentionally
targeted by collectors.
Despite their good survival in tanks, and ease
of propagation, the photosythetic gorgonians
have a number of issues which may be important
to aquarists; many ship poorly and foul their
bag water. Having collected gorgonians and seafans,
the amount of purplish-gray secretions and mucous
of some species is astonishing, and transport
seems nearly impossible if more than a few hours
elapse from ocean to tank. Furthermore, these
species are well-endowed with rich chemical
arsenals of secondary metabolites which must
be considered in terms of their impact on sensitive
tankmates. Gorgonians produce an incredible
diversity of complex and biologically active
compounds, many of which are being investigated
for pharmacological potential.
potential drawback to gorgonians is their size.
Some species become absolutely huge, and few
tanks would be able to maintain an adult colony
of some of the large fans and tree-like colonies.
Others, fortunately, remain "aquarium-sized."
The encrusting gorgonians, such as Erythropodium
spp. and Briareum spp., can be very aggressive
and fast-growing, quickly overtaking almost
anything in their way. It is best to consider
carefully the purchase of these species, and
make allowances to prevent a tank from quickly
becoming a living carpet of encrusting gorgonian.
is a very large group of corals, most of which
will never be seen in the aquarium trade. Properly
selected, gorgonians make exceptional candidates
for aquaria and for captive propagation. Many
of them, however, are currently unable to be
maintained in closed systems, with a very few
having occasional reports of success in an individual
tank. It is best to leave the species with difficult
husbandry needs in the ocean. If, however, one
finds themself in possession of one of the more
beautiful and hard-to-keep species, it should
be mentioned that it will likely need a very
large amount of fine particulate food sources,
possibly including phytoplankton as a component.
Detritus, bacteria, and pseudoplankton in very
small size classes may be the best choices,
if available. Remember, seafans should always
be positioned perpendicularly to water flow!
Other tips on gorgonian placement and husbandry
are listed in the book, Aquarium
Corals, by Eric Borneman.
Text by Eric Borneman.
Photos by Reef Central members.
Reefkeeping Magazine Reef Central, LLC-Copyright © 2008