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Much of
Oculina Banks now looks like this. Dead Oculina
coral fragments, the dark material on the bottom, are
strewn about as rubble. Scientists are attempting to
restore Oculina habitat at this site on
Sebastian's Reef. Note the reef ball in the distance
(far right just beyond the illuminated area), which was
placed there as a potential substrate for the coral and
to simulate fish habitat. Click image for
larger view. |
| | Coral Reef Restoration
September 2,
2001
Chris Koenig
Research Marine Ecologist
Department of Biological Sciences
Florida State
University
 View
a video of reef balls, which are being used to restore the coral
growth and re-establish fish habitat. (5.6 MB,
QuickTime
required).
Background
In 1975. scientists from the Harbor
Branch Oceanographic Institution (HBOI) used manned submersibles to
dive on the Oculina Bank area and discovered the coral community
there. At the time, many of the pinnacles and ridges of the
300-sq-nm Banks teemed with grouper, snapper, and amberjack in dense
stands of ivory tree coral (Oculina varicosa). By the early
1990s, however, the fish populations dwindled severely, and most of
the coral habitat had been destroyed.
The scientists who
discovered the banks recognized the fragile nature of the coral and
its significance to the most important reef fishery species in the
South Atlantic, gag and scamp grouper. By 1984, they convinced the
South Atlantic Fisheries Management Council (SAFMC) to designate 92
sq nm -- about one-third of the bank -- as a Habitat Area of
Particular Concern (HAPC). In 1994, the SAFMC declared the same area
an experimental research reserve, where, for the next 10 yrs,
trawling, dredging, and bottom fishing would be
prohibited.
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Oculina coral
fragments at different stages of decay. The piece on the
left has been dead for a short time; the round calyx
structures, where coral polyps attach, are still
visible. The next two pieces (second and third from the
left) have been dead longer, perhaps six months to a
year, and are beginning to show signs of colonization by
other reef animals. The two pieces on the right have
probably been dead for 1-2 yrs. They are heavily
encrusted and discolored by tube worms, sponges, and
other boring organisms. Click image for
larger view. |
| | When we
dove on the Banks in 1995 to study the fish populations, one
scientist who had discovered the Banks was stunned by the
destruction of the Oculina habitat since observing it in the
1970s, prior to a period of intense bottom trawling for shrimp and
scallops. Naturally, we wondered whether the coral's destruction and
failure to reproduce were linked to this activity or to some natural
phenomenon. With knowledge of this broad- scale loss of
Oculina habitat, the SAFMC made restoring the habitat the
highest priority.
An Experiment with Reef
Balls
For the next six years, we experimented with
reestablishing the Oculina corals. Originally, we wanted to
test whether living Oculina could survive if we put it
anywhere in the reserve, and whether it could settle and grow on a
clean concrete surface. For three years, beginning in 1996, we
deployed 56 sets of concrete-block clusters, or reef balls,
throughout the reserve, in hopes of restoring the Oculina and
simulating its habitat. About half of the reef balls were set out
with coral attached, and the other half were bare. When we returned
to look at the reef balls in 1999, we discovered that on the ones
where coral remained attached, the coral was alive. On some blocks,
the coral appeared to have been stripped off. Of the balls set out
without attached coral, only one showed coral recruitment.
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These concrete
blocks were the first artificial structures deployed to
provide a substrate for reestablishing Oculina coral and
simulating fish habitat on Oculina Bank. Click image for
larger view. |
| | In 2000,
we decided to deploy commercially available, dome-shaped reef balls
about 3 ft in diameter with holes for the fish to swim through.
Their shape actually resembles an Oculina coral head. We
dropped these off a stationary ship in three sets of 5, 10, and 20
reef-ball clusters (a total of 105 reef balls), all with
Oculina coral attached. ( Watch
a short video that shows three of these deployed reef
balls.)
Near each cluster of reef balls, we also deployed
25 patio stones, each with a small fragment of Oculina
attached to a single PVC pipe fastened vertically to the center of
the stone. This was an experiment to evaluate how small a fragment
could survive and grow. We did this because the smaller the fragment
that can survive, the less coral must be removed from donor sites to
aid in restoration.
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A speckled
hind is about to enter one of the reef balls deployed at
Sebastian's Reef in September 2000. Scientists are
encouraged by their observations of more fish at the
reef-ball sites during this leg of the Sustainable Seas
Expeditions/Islands in the Stream South Atlantic Bight
Mission. Click image for larger view. |
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An Apparent Initial
Success
Yesterday, explorers descended to a
depth of more than 300 ft in the Cleliasubmersible to search
for the reef balls deployed last year. We found all of the sets, but
not all of the reef balls in each set. From our vantage point in the
Clelia it is still too early to tell how successful we have
been in reestablishing Oculina, since it grows only about
one-half inch per year. To our delight, however, it appears that we
are in the initial stages of reclaiming this habitat for the fish
that belong there. We observed that the reef balls have already been
colonized by groupers, amberjacks, snappers, angelfish,
butterflyfish, and small basses.
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Oct. 1 Log
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