Neoplasm
(calicoblastic
epithelioma)
on elkhorn
coral
Acropora
palmata,
Florida Keys.
The yellow
color is due
to the
formaldehyde
solution used
to fix tissues.
Photo by
E. C. Peters |
 |
| Appearance |
White, protuberant, irregularly shaped, calcified masses or tumors,
covered by a thin layer of translucent tissue, occur on the surfaces of
branches of Acropora spp. and other members of the acroporid and
pocilloporid families of hard corals (see papers by Cheney,
1977; Bak, 1983; Peters,
Halas, and McCarty, 1986; and Coles and
Seapy, 1998). |
Close-up
of margin of
a tumor on
Acropora
palmata
showing the
"bubbling"
appearance
of the tissue,
Florida Keys.
Photo by
E. C. Peters |
 |
Appearance
- continued |
The polyps of the coral colony are each encased in an asymmetrical
tubular skeleton known as a corallite. The coenosteal skeleton is more
porous and connects the polyps by tiny canals, facilitating the exchange
of nutrients throughout the colony. In the area of the tumor, the polyps
disappear from the margin of the tumor toward its center, and there is
an increase in the coenosteal skeleton, so that the center of the tumor
has a smooth appearance. The tissue at the margin of the tumor can have
a "bubbled" appearance, indicating rapid cell multiplication. |
Large
calicoblastic
epithelioma
on Acropora
palmata,
Florida Keys.
Circular
area has
been
colonized
by algae,
probably
due to loss
of mucus
secretory
cells from
the tissue.
Photo by
E. C. Peters |
 |
Appearance
- continued |
The cells found in the tumor resemble the more metabolically active
and rapidly dividing cells of the growing branch tips, and like the branch
tips, also lack the symbiotic algae. The epidermis covering the tumor also
loses the mucus secretory cells that help remove sediments from the coral
surface. The result is that sediment accumulations lead to tissue death
and invasion of the skeleton by algae and boring organisms.
The presence of the tumors on a branch is also associated with a decrease
in, or halting of, branch tip growth, suggesting changes in the transport
of nutrients in the colony. This locally invasive abnormal mass of tissue
and unusually porous skeleton grows faster than the surrounding normal
tissue and skeleton. It proceeds to destroy the polyps and cause the death
of the coral tissue.
Based on these factors, this condition has been termed a neoplasm (cancer),
calicoblastic epithelioma. |
| Cause |
The cause(s) of neoplasms in hard corals are unknown. Probably mutations
of the genome and/or programmatic changes in gene expression of the coral
cells are responsible for these skeletal anomalies, but whether a particular
agent, such as ultraviolet radiation, is responsible for a particular mutation
has not been determined. Additional studies are needed. |
| Distribution |
Calicoblastic epitheliomas have been found on acroporid corals from
Guam, Enewetak, Gulf of Oman, Netherlands Antilles, and Florida Keys, often
in a "clumped" pattern. |
| Impact |
Calicoblastic epitheliomas are capable of damaging portions of coral
branches, leaving them more susceptible to invasion by boring organisms
which can lead to increased breakage and fragmentation, in addition to
destroying the normal polyps by which the coral produces eggs and sperm
for sexual reproduction. |