[Coral-List] Lionfish and African Dust
Eugene Shinn
eugeneshinn at mail.usf.edu
Wed Feb 5 15:51:18 EST 2014
After reading remarks by Doug Fenner, Matt Johnson, and Samuel Purkis
regarding my short note relative to lionfish and /Diadema,/ it occurred
to me that readers might have missed my point. It has been 14 years
since we hypothesized that the 1983 Caribbean-wide near die-off of
/Diadema/ and acroporid corals, and initiation of sea-fan disease, were
likely caused by something carried in African dust *(Shinn et al., 2000,
African Dust May be Cause of Coral Death. Geophysical Research Letters,
v. 27, no 19, p. 3029-3032).* The smoking gun, /Aspergillus sydowii/ (a
soil fungus), shown by Smith et al. (1996) using Koch's postulate, was
the cause of the sea-fan disease. That African dust had negative
environmental effects was regarded as an outrageous idea. However,
abundant research has been conducted over the past 14 years that shows
the good as well as deleterious effects of African dust on the environment.
African dust passing over the Cape Verde Islands is now widely
recognized to hinder hurricane formation (some meteorologists still call
it dry air). Iron in dust has been proposed to stimulate red tides, and
iron is now recognized by chemical oceanographers (as originally
proposed by John Martin) to stimulate primary productivity in the open
ocean. Ligands in seawater are recognized for their ability to convert
insoluble iron to bioavailable iron. That such dust clouds carried by
trade winds often blanket the entire Caribbean has been repeatedly
demonstrated in NOAA and NASA satellite images. The year 1983, a major
El Niño year, correlated with coral bleaching in the eastern Pacific off
Central America. Interestingly, major bleaching in the Caribbean and
Florida did not occur until 1987. Besides being an El Niño year, 1983
was the peak year of African dust flux to the Caribbean as measured at
the Barbados monitoring station in operation by Joe Prospero since 1965.
Dust flux at his station began rising in 1980 and continued to rise each
year, culminating in the peak year 1983. Levels fell a little in 1984
and 1985 (dropped to the 1981 level in 1986) but rose again in 1987
before dropping back to 1979 levels. These were all significant years
for coral distress, and diseases were reported well before 1983. In
fact, black-band disease in brain coal was reported in Bermuda in 1973,
which was also an earlier peak year for dust flux at Barbados.
Correlation is not proof of causation of course, but correlation is
certainly a stimulus for further research. In the case of African dust,
no systematic experiments (controlled bioassays) other than the work on
sea-fan disease have been conducted to test the hypothesis. Likewise,
there have been no systematic controlled bioassays conducted on the
effects of sewage pollution. The supposed association of sewage effects
has also been one of correlation. Fortunately, some controlled
experiments are now being conducted on the effects of sunscreen
ingredients and pesticides on corals. One should wonder why such obvious
experiments were not conducted years ago considering the seriousness of
coral demise.
However, we now know more about the composition of African dust which,
although dominated by silica, also includes P, Fe, Hg, Au, Al, Be-7,
Pb-210, and in fact, most all of Earth's elements. Be-7 is a radiogenic
gamma-ray emitter with a short half-life of only 53 days. It is produced
high in the stratosphere by cosmic-ray spallation of nitrogen atoms and
is continually raining to Earth at low levels but somehow becomes
concentrated in dust clouds that reach the Caribbean. The levels of Be-7
in the red sediment that accumulates in rainwater cisterns on Caribbean
islands is many orders of magnitude greater than that ordinarily found
in lawn grass. People in the Windward Islands and elsewhere in the
Caribbean ordinarily breathe the dust during periodic dust-flux events
whose densities often cause closure of airports on Caribbean islands.
Residents there are well aware of its effects on respiratory systems.
African dust also carries modern pesticides (some, such as DDT, still
used in the Sahel region of Africa, are known immunosuppressants). The
dust also transports many viable microorganisms.
USGS microbiologists have identified a profuse and diverse microbial
community in airborne African dust; many microbes identified to the
species level (bacteria and fungi) are known pathogens for plants and
humans. The impact or influence of viruses associated with these
globally dispersed dust storms is just beginning to be explored. Given
that we can only culture approximately 1% of bacteria in any given
sample type, the true extent and influence of these microbes that fall
out of the atmosphere in downwind environments has only been touched upon.
So how does lionfish distribution support the dust hypothesis?
Regardless of where the infestation began (probably in multiple
locations), it took several years for the lionfish to be observed in the
Windward Islands. Does anyone know exactly when the fish arrived there?
I do not. For them to reach those islands, they would have to have moved
against strong prevailing east-to-west currents. Alternatively,
migration would require a circuitous route. After establishment in the
Bahamas (where they were abundant before they were observed in the
Florida Keys), they would then have to have worked their way
southeastward to the northern Windward Islands and slowly emigrate
southward along the island chain. From what I have read, it remains
unclear whether they have bridged the current-swept gaps to reach the
southernmost Windward Islands. At any rate, they apparently did not
reach the Windward Islands as quickly as the /Diadema/ disease.
Now consider the /Diadema/ die-off events as reported in a comprehensive
paper *(Lessios et al., 1984, Spread of /Diadema/ mass mortalities
through the Caribbean. Science, v. 226, p. 335-337)*.According to those
authors, mortalities began in the vicinity of the Panama Canal in the
southwestern part of the Caribbean (the disease agent was initially
thought to have come from a ship's bilge water) and within one year
spread over the entire Caribbean including the Windward Islands. To
accomplish this, the unidentified infecting agent, unlike swimming fish
or fish larvae, had to have traveled against the strong prevailing
east-to-west current that passes through the Windward Islands chain.
Spread of the disease also reached remote Bahamian islands such as San
Salvador and Rum Cay within one year. I do not know how long it took
lionfish to reach San Salvador, but I suspect it was more than a year.
Surely someone on that island likely knows when the fish first arrived.
These were the kinds of observations that initially led us to
hypothesize that the infecting agent, whether elemental, chemical, or
biological, had settled throughout the southern Caribbean from African
dust clouds. The level of dust flux had been rising for several years
before peaking in 1983. Dust levels remained high and did not subside to
levels recorded between 1965 through 1968. Various coral diseases have
not subsided since 1983, and although /Diadema/ exists in pockets
throughout the Caribbean, pre-1983 levels have not been reported. They
are extremely rare in the Florida Keys. One should remember that once
material in the dust lands in the water, currents would then carry the
agent northward in the manner that they transport Caribbean-derived
lobster larvae that mature in the Florida Keys.
For reasons discussed, the relatively delayed arrival of lionfish in the
Windward Islands versus the rapid Caribbean-wide dispersal of the
/Diadema/ disease lends support to our original hypothesis that whatever
infected /Diadema/, acroporid corals, and sea fans had dropped out of
the atmosphere. That the levels of dust flux had been increasing for
several years likely caused local outbreaks of coral disease. Key
observations of reefs in St. Croix support this supposition.
Nevertheless, the peak of coral disease and the/Diadema/ die-off
occurred in 1983. Donald Gerace, head of the Finger Lakes Laboratory at
San Salvador, described to me how a well-known nearshore /Acropora/
/cervicornis /reef had begun to die in a short period of time (less than
2 months) during the summer of 1983. Those corals were entirely dead
when I swam over the reefs with Phil Dustan a few months later. In
addition, most all /A/. /palmata /around the island was also dead but
still standing. Some time later, I observed similar dead acroporids
around nearby Rum Cay, where locals told the same story we heard at San
Salvador. San Salvador and Rum Cay are both surrounded by deep-Atlantic
water and are isolated eastward of the other Bahamian islands. In
Florida, acroporids showed signs of stress in the late 1970s as revealed
in serial photographs that date back to 1960. These photographs clearly
show that the main period of sudden and synchronous demise at the photo
sites occurred in 1983. At San Salvador, acroporid death was sudden.
The red soil on San Salvador (called pineapple loam) is derived from
African dust, and pottery there that pre-dates the arrival of Columbus
was made from clay that had been fired. The only source of clay minerals
in the Bahamas is African dust, the influx of which is not new. What is
new is what the dust contains today.
In conclusion, the apparent delayed arrival of lionfish to the Windward
Islands versus the swift and synchronous outbreak of /Diadema/ disease
throughout the Caribbean is considered supportive of the African dust
hypothesis.
The recent identification of /Serratia marcescens/ in Florida Keys coral
is a good step toward solving an evolving mystery. However, evidence
that human fecal bacteria, and other elements in sewage, caused
acroporid death simultaneously throughout the entire Caribbean,
especially at sparsely populated isolated locales such as San Salvador
seems a stretch.
Gene
--
No Rocks, No Water, No Ecosystem (EAS)
------------------------------------ -----------------------------------
E. A. Shinn, Courtesy Professor
University of South Florida
College of Marine Science Room 221A
140 Seventh Avenue South
St. Petersburg, FL 33701
<eugeneshinn at mail.usf.edu>
Tel 727 553-1158
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