Dust and other Hypotheses

[Gene Shinn]

Dear Coral Listers,
Since there has been so much discussion of the African dust hypothesis on
the list in recent weeks, I could resist responding no longer. First, the
experiments proposed by Jim Hendee to test African dust effects on corals
are similar to ones I have been proposing for at least 5 years.
Unfortunately, there is little funding to do such work. In addition, the
USGS does not have in place the dust collectors you mention. We sample for
microbes using very small samples and collection requires only 10-to-15
minutes. We do no routine monitoring but would if we could. There is no
funding for the large expensive samplers needed to provide enough sample for
the experiments Jim proposed. Secondly, the major problem with finding the
Diadema pathogen is that the pathogen that first killed them has not been
identified so we do not know what to look for. It would be possible,
however, to test living Diadema against those microbes that have been
cultured from dust thus far.
I thank Lessios for answering Alina's question regarding survival of West
African Diadema. I did not have an answer as elegant as his. I could only
suggest that Diadema living so close to the source, like the humans and the
Siderastera sp. that survive there, long ago adapted and those that didn't
died. Lessios also makes some very valid points regarding water transport of
the unknown pathogen. We accept that the Diadema die-off began near the
Panama Canal (Lessios et al., 1984, Science, 226:335-337). We also point out
that the die-off began in winter when African dust impacts the southern
Caribbean, South America and the Panama region and it was also the dustiest
year since Prospero began monitoring dust in 1965. The upper Caribbean is
impacted later during the summer months. Like Lessios, we believe water
transport is very important. How else would it infect Diadema in aquaria (I
assume we are talking running seawater aquaria)? Once the Caribbean basin is
impacted as shown in the NOAA satellite image in our 4-page info sheet in
our website, water currents likely complete the distribution of any
pathogens delivered from the air. Areas downcurrent, such as, Belize and
Florida, were impacted by the disease after Panama. What has concerned us,
however, is how did the pathogen later move hundreds of miles against the
Caribbean Current to reach the Lesser Antilles? Dust contamination of the
Atlantic seaward of the Antilles and then transport downcurrent to the
Antilles seems a reasonable possibility. There is nothing between the
Antilles and Africa, and both the wind and the currents move toward the
Antilles. More recent studies conducted by microbiologists at our office
show that microbial species in dust can change drastically within 30
minutes. Don't expect a dust cloud to deliver the same microbes everywhere
at the same time.
My main point is that the dust hypothesis is just that, an hypothesis, as
are the other proposed causes of Diadema and coral death. The ballast-water
origin is an unproven hypothesis, as are the other "usual suspects" that
drive coral research funding. This latter point gets back to what Jim
pointed out a week earlier regarding the emotional "pollution" word. Where
is the original basic research demonstrating the degree of damage done to
corals by the "usual suspects," oil spills, sewage, sedimentation, and
mosquito spraying, to name a few? We seem to have skipped over the basics
and then let assumptions and emotion guide our research and funding
agencies.
Best Wishes, Gene

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http://coastal.er.usgs.gov/african_dust/ |
E. A. Shinn
email eshinn at usgs.gov
USGS Center for Coastal Geology |
600 4th St. South | voice (727) 803-8747 x3030
St.Petersburg, FL 33701 | fax (727) 803-2032
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