Basic HTML Version
The GreaT PlaGue
In the spring of 1983 the coral reefs of the Florida Keys were
quite different than they are today. Although they faced the
pressures of high visitation, pollution and extensive fishing,
absolute coral cover was stable at around 25 percent. This
was down from the 50 percent of the early ’70s, but live
stony corals were still the dominant living structures of
Keys reefs. On each coral head and in every rubble patch in
the Keys there lived at least a few purple-black sea urchins
with long, pointed spines, known for skewering wetsuits
and unwary hands. Then, over the course of a single week
in July 1983, the urchins were all dead or dying. Diadema
antillarum were suddenly only a memory.
In only one year, beginning in January 1983, the Diadema
plague extended from the southern Caribbean north to
Bermuda. As currents spread the pathogen, 92 to 99 percent of
all the billions of Diadema sea urchins in this vast 1.4-million-
square-mile oceanic habitat died within 13 months. This was
the most extensive mass mortality of any marine animal ever
reported, and the species was suddenly very near extinction.
Diadema are (were) the keystone herbivores of the
tropical western Atlantic reefs. They consume the macro
algae that overgrow reefs, and their feeding activity cleans
and scrapes the limestone substrates, stimulating settlement
of coral and other invertebrate larvae. Without herbivores
like Diadema, algae rapidly overgrows corals, greatly
reducing sunlight, trapping sediments and even waging
chemical warfare on coral tissues. Now, almost 30 years
after the massive die-off, a limited return of the Diadema
populations has occurred elsewhere in the Caribbean but
not in the reefs of the Florida Keys. Ecological recovery
of the Keys’ coral reefs is simply not possible without the
return of Diadema.
When DiaDema reTurn
Ken Nedimyer and I, both marine biologists and members
of the Florida Keys National Marine Sanctuary Advisory
Council, conducted a study to demonstrate what would
happen if Diadema returned to the reefs. In the fall of 2001,
with the support and counsel of the Marine Sanctuary staff
and the National Undersea Research Center (NURC) of
the National Oceanic and Atmospheric Administration
(NOAA), we began work on a Diadema restoration project.
This project transferred at-risk juvenile urchins from
rubble zones to deeper reefs to see if they could survive
relocation and, if they did survive in adequate numbers
(about one urchin per square meter), whether they could
change the ecology of the reefs. We selected four small,
25-foot-deep patch reefs west of Pickles Reef near Key Largo.
We introduced urchins to two of them — the experimental
reefs — and observed the other two as control reefs. NURC
assessed the ecology of all four reefs before and one year after
relocation of the Diadema urchins. The ecological effects of
the relocated urchins on the two experimental reefs in the
short space of one year were remarkable.
On the experimental reefs, stony coral cover increased 59
WATER PLANET
104
|
WINTER 2012
Diadema, Caretaker of the Reefs
B y M a R T I N M o E
Martin Moe rears Diadema
from planktonic larvae to
juvenile urchins in his lab.
The culmination of his work
will be the reintroduction of
these crucial herbivores to
Florida Keys coral reefs.
P HO T O S T H I S P A G E : T I M GRO L L I MUND
104-105_Water_Planet_Winter2012.indd 104
12/20/11