[Coral-List] poleward migration of corals

[Gene Shinn]

Regarding coral range expansion. In the late 1960s Acropora palmata 
from Florida was transplanted to Bermuda where it does not grow 
naturally. The experiment was conducted twice. In both cases winter 
low water temperature caused their death.
The experiment was conducted to test the prevailing view that this 
species was absent because the larvae of this species could not make 
the trip. We did not prove they could not go that far but a possible 
implication of this little experiment might be that with global 
warming Acropora species may someday take up residence in Bermuda.
It should also be pointed out that Precht and Aronson, and I think 
some others, found living A. palmata in 2002 at the Flower Gardens 
marine sanctuary in the northern Gulf of Mexico. This reef 
accumulation on a salt dome had been studied for decades by 
researchers from Texas A and M without detection of this tropical 
species. More recently Precht and Aronson also found fossil A. 
palmata at the Flower Gardens that dates around 6,000 years before 
present (Holocene thermal maximum when global temperature was higher 
than today) and more recently they discovered abundant fossil A. 
cervicornis (staghorn coral) that is likely younger than the A. 
palmata (Precht personal communication). Is the return to a warmer 
ocean causing expansion of Acropora back to the Flower Gardens?
I would like to point to the recent publication in Coral Reefs by Banks et al.,
Volume 26, Number 3 / September, 2007 that describes the highlights a 
huge shelf edge Acropora reef (with clearly defined reef flat 
indicating former sea surface) that flourished off Ft. Lauderdale, 
Florida but died approximately 7,000 years ago. Geologists have known 
of this dead reef since the early 1970s because of outcrops made by 
trenches for sewer out fall pipes. The reef was first described at 
the 1977 International Coral Reef Symposium and later in Science. In 
another paper in the recent issue of Coral Reefs (Macintyre et 
al.,Vol 26, No 4, Dec) provide 29, 14C dates of transported A. 
palmata collected from 9 different sites along Cobblers Reef at 
Barbados. Cobbler reef is a dead 15-km-long linear reef that 
accumulated to approximate present day sea level. The dates range 
from about 350 to 4,500 years before present. What was the 
environmental crisis that killed this reef? The dates clearly show 
death of this threatened species began long before human population 
and sugar cane production that began on the island about 350 years 
ago. The authors suspect periods of increased hurricanes. At any rate 
something was happening to the climate.
Recently completed maps and review of the Florida Keys National 
Marine Sanctuary by the USGS show that more than 90 percent of what 
biologists have been calling a coral reef is actually a thin veneer 
of coral and algal growth ranging between a few cm to about 2 m in 
thickness (Lidz et al 2008). This so-called reef tract, 25 to 35 ft 
deep, has been flooded for more than 6,000 years. One wonders why has 
there been so little reef accumulation? Should it be called a reef or 
a hard ground community? The thickest coral accumulation along the 
platform margin is in the spurs and grooves that built the major 
named reefs, ie., those with lighthouses. The individual spurs, 3 to 
5 m thick, are located along the outer margin of the shallow shelf 
and are composed of A. palmata as revealed in drill cores, ship 
grounding scars, and other methods, are rooted directly on underlying 
Pleistocene limestone. These spurs ceased growing more than 2,000 
years ago and today (since 1950) are coated mainly with Millipora. 
The thickest reefs occur landward of the platform margin in places 
like Grecian Rocks. The reefs there are thicker, up to 45 ft,.
A recent study of 39 fossil A. cervicornis sticks collected from the 
sand along a hundred-mile-long stretch of the Florida Keys reef tract 
(Shinn et al 2003) revealed two 500-year periods of staghorn coral 
demise. One centered at approximately 3,000 years ago and a more 
pronounced hiatus centered at 4,500 years ago. What caused mortality 
of this threatened species? With all this accumulated background 
information should we not be wondering what caused all that death and 
destruction at a time when we can safely rule out anthropogenic 
influences. There is currently a lot of hand wringing and hysteria on 
the coral-list over coral death during the past 30 years and most 
point to the "usual suspects" but the big mystery remains. We had 
even more widespread and longer lasting coral adjustments during the 
past 7,000 years than during the last 30 years. Should we not be 
trying to find out why? Possibly such studies might determine the 
cause of Caribbean-wide coral death during the past 30 years. All the 
supporting data and references can be found in Lidz et al (2007). Gene

Lidz, B.H., Reich, C.D., and Shinn, E.A., 2007, Systematic Mapping of
         Bedrock and Habitats along the Florida Reef Tract: Central Key Largo to
         Halfmoon Shoal (Gulf of Mexico): U.S. Geological Survey 
Professional Paper
         PP 1751 (300+ single-spaced hardcopy pages: DVD and online at
         http://pubs.usgs.gov__________).


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No Rocks, No Water, No Ecosystem (EAS)
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E. A. Shinn, Courtesy Professor
University of South Florida
Marine Science Center (room 204)
140 Seventh Avenue South
St. Petersburg, FL 33701
<eshinn at marine.usf.edu>
Tel 727 553-1158---------------------------------- 
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