Invertebrate
Predators on Octocorals
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Fireworm feeding on a branching gorgonian, Psuedoplexaura
sp.
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Two
types of snails (the flamingo tongue Cyphoma and the small
coral-eating snail Coralliophila) and the fireworm (Hermodice)
commonly feed on Gorgonians.
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Flamingo
tongue snails are pale orange in color and have a colorful mantle
(orange with black spots) that extends over their shell. The mantle
is retracted when the snail is disturbed.
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Flamingo tongue feeding on a branching gorgonian, Eunicea spp.
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Five
Cyphoma snails feeding on a sea fan, Gorgonia ventalina
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They
occur in small aggregates (2-20 snails), and leave a characteristic
feeding scar that extends in a narrow line up the blade.
Cyphoma snails typically graze tissue in a trail that extends
across the blade, exposing the spicules (hard, needle-like spines
in the tissue) and the main stem (axial skeleton). |
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The
other gorgonian eating snails Coralliophila caribea,
typically stay close to the holdfast at the base of the sea fan
and often cause small lesions. They occur in small aggregates on
a sea fan or sea plume, and typically cause little tissue loss.
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Two Coralliophila caribea coral snails on elkhorn coral, A.
palmata |
Snail
Predation on Stony Corals
Coralliophila snails have a characteristic yellow/orange
operculum (the hardened plate that is attached to their foot).
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The snail Coralliophila abbreviata feeds on over 20 species
of stony corals and occasionally on soft corals. |
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In
general, smaller snails live at the periphery of dead areas, at
the base of a colony, or under the margin of a flattened plate,
and only emerge at night to feed; often grazing scars are not apparent.
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Coralliophila snails on flower coral, Eusmilia fastigiata
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Coralliophila snails on elkhorn coral, A. palmata
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Larger
snails are found most frequently on elkhorn coral, where they aggregate
in the open on upper or lower branch surfaces. They create prominent
grazing scars that slowly increase in size from ongoing snail predation
and may ultimately kill the affected coral.
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Coral
eating snails (C. abbreviata) generally occur in aggregates
of 2-20 animals, but occasionally they may be
more abundant. For example, a single colony of lobate star coral
M annularis may have several hundred snails.
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Star coral, M. annularis with Coralliophila snails |
A large aggregate of Coralliophila snails on elkhorn coral,
A. palmata |
The
snails are usually well camouflaged on massive and plating corals,
and can easily be missed as their shells become completely encrusted
with algae and small invertebrates. Snails are typically much larger
when found on elkhorn coral (A. palmata) and staghorn coral
(A. cervicornis) and will remain out in the open on upper branch
surfaces. |
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Snail predation may be confused with White-Band
Disease and other syndromes that affect elkhorn or staghorn
coral. Snails may begin to consume coral tissue from the base of
the colony, and progressively eat their way up the coral. But, unlike
WBD which forms a very regular band, snails remove tissue only directly
below their shell, which creates a scalloped pattern. Close examination
of the live tissue adjacent to the exposed skeleton will not appear
diseased or be peeling off the skeleton as is often observed with
WBD.
It
is important that the presence of snails is used as one diagnostic,
but not the only diagnostic sign of snail predation, as snails often
eat small patches of tissue, and may retreat to the base of the
coral during the day or for several days when not feeding.
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