[Coral-List] David Hopley, reef dredging mud and J. Harold Hudson PhD.

Gene Shinn eshinn at marine.usf.edu
Wed Feb 7 14:19:00 EST 2007

Dear David, Your posting about dredge-mud and turbidity 
concentrations was very interesting. The levels expressed (as mg/l) 
that did not kill corals are high but not a complete surprise. They 
are probably higher than most coral biologists would be willing to 
accept. When I first responded to the dredge mud question I avoided 
specific numbers because the numbers we had generated in the past 
seemed high considering the poor state of coral reefs today. Around 
30 years ago in the mid 1970s we funded and hosted Jack Thompson's 
dissertation work on corals at Fisher Island Station. Corals were 
still healthy then and there was growing concern over effects of 
drilling mud. Because of that concern we were funded by the USGS 
Conservation Division that later merged with parts of the Bureau of 
Land Management to become the present day Minerals Management 
Service. Data was urgently needed to make rational decisions 
regarding offshore drilling. Congress was even considering a Federal 
Oil Company.
       Most of Thompson's Texas A and M dissertation was published in 
an obscure Elsevier book (MARINE ENVIRONMENTAL POLLUTION, 1, Richard 
A. Geyer editor). The book was published in 1980. I suspect few coral 
researchers have ever seen the book. Here is a quick summary.  As a 
team we published 3 chapters in the book. Thompson's chapter (16) 
      In these studies seawater and carbonate mud from Florida bay, 
were used as controls and results were also compared to sediment 
stirred up by boats in Hawk channel (including the glass bottom boat 
that usually made 3 trips/day in Pennekamp state park and the Key 
Largo Marine Sanctuary. One of the most unexpected finds was that 
clear water from near the entrance to Miami's Government Cut that we 
pumped into our lab at high tide killed corals quicker than any mud 
concentrations we tested. It was our first realization of how 
effectively microbes could kill coral. Because of this, Thompson was 
forced to make weekly trips 6 miles out in the Gulf Stream for clean 
Sediment/mud content was determined and expressed as mg/l based on 
weighing Millipore filters. The duration of the tests were the 
standard 96 hours.
      In summary we learned from Thompson's laboratory and field tests 
that after 96 hrs all seven species showed behavioral effects but 
none died at levels up to 150 mg/l. At 476 mg/l M. annularis and 
Agaricia agaricites were killed after 65 hrs. Acropopra cervicornis 
was killed after 96 hrs in one test but survived in another test. Why 
one survived and the other did not could not be determined. The other 
species, Dichocoenia stokesii, Porities divaricata, Porities 
astreoides, Porities divaricata survived 96 hrs exposure in the high 
concentration but showed extreme behavioral response, i.e., retracted 
polyps etc.
      Thompson's field tests were unique. They were performed in 
closed 22-liter glass aquaria (sealed glass lids) in 3 m of water 
adjacent to the Carysfort lighthouse on Carysfort reef. The also 
lighthouse served as a base of operations for a group of graduate 
students from Texas A and M University. Small plastic bilge pumps in 
each aquaria maintained particle suspension and the water was changed 
daily and new mud added to maintain concentrations. To put the data 
in perspective Griffin (1976) had measured 40 mg/l (lime mud) in the 
wake of a barge tug combination in Hawk Channel in Pennekamp park. 
Three hours later it had dropped to 14 mg/l while concentration 
outside the plume was 3 mg/l. A surface sample of Mississippi river 
water we collected from mid river near Venice La was 41 mg/l.
     The study of drill mud plumes around 7 different oil rigs in the 
northern Gulf of Mexico (Chapter 18) revealed ranges from 11 to 80 
mg/l only 1-meter from the discharge pipe! Concentrations ranged from 
1.40 to 11.32 mg/l in the plume 96-m from the discharge pipe. Average 
background of samples taken upstream of platforms was 2 mg/l, much of 
which was salt and plankton. None of the samples were leached in 
distilled water to remove salt before weighing. Compared with 
Thompson's test one could conclude that all the corals tested could 
have survived 96 hrs only 1 meter from the discharge pipe (assuming 
the muds were all of the same composition). Clearly they would 
survive much longer 96 m from the source. These were surprising 
results because drill mud plumes are sometimes visible from the air 
up to 1 km downstream from rigs when drilling is in progress.
      The chapter by Hudson et al (Chapter 17) has two parts. While 
Thompson was doing his bioassay at Carysfort reef the team of Texas A 
and M students lead by Tom Bright were conducting other tests. Knobs 
from a single Montastrea sp were cemented to tiles. And monitored 
using closed circuit TV. Every few hours (night and day) a student 
diver would squirt drill mud paste (resembling tooth paste) on one of 
the heads. The mud mucus combination formed a layer a few mm thick 
over the coral. Within hours polyps swelled and in conjunction with 
wave and tentacle action the mud was shed. None of the corals were 
killed after repeated applications. These test corals were allowed to 
remain on the reef for 6 months at which time they were collected by 
Hudson for slicing, X-ray photography, and sub samples were analyzed 
for barium (the common ingredient of drill mud). Data revealed that 
barium had been incorporated in the skeleton but measurement of 
growth rings indicated that growth rate was not affected. Growth rate 
was compared to the previous 5 years of growth of the same specimen. 
Hudson later used the same technique (in 25 m of water) at a drill 
site off the Philippines. The mud had minimal effect on growth rate. 
(Hudson, J. H., et al., 1982, Effects of offshore oil drilling on 
Philippine reef corals: Bulletin of Marine Science, v. 32, no. 4. P. 
890-908) In the same chapter Hudson also measured annual growth rings 
from 12 cores of Montastrea sp taken in 20-m of water at East Flower 
Gardens off Texas. The major finding was a significant reduction in 
growth rate that occurred simultaneously in all 12 heads in 1957. 
Growth rate dropped from a 50-year average of 8.9 mm/yr before 1957 
to 7.2 mm/yr after 1957. Samples of skeleton representing growth from 
between 1969-74 were analyzed for barium and chromium but none was 
found although offshore drilling had been occurring throughout the 
northern gulf for many years. The cause of growth rate reduction in 
1957 was not known but later information suggested a sudden increase 
in water depth due to collapse of the underlying salt dome. This is 
still an open question.
      The results for these three studies (Chapters) had important 
implications, however, to my knowledge they never influenced offshore 
drilling policy one way or the other. All of these studies were very 
field-work-intensive and may never be duplicated. Diving regulations 
alone would require a mountain of paper work today. It is however, 
reassuring to see that data from 30 years ago falls in the range of 
recently determined concentrations reported by David Hopley. The 
exact composition of the drill mud that we used was not precisely 
known but in all likelihood was more toxic than typical dredge mud in 
a coral reef setting. Drilling mud concentration and composition 
constantly changes as the drill bit get deeper and deeper. It should 
also be pointed out that dredging usually lasts more than 96 hrs. A 
good recommendation would be to limit active periods of dredging to 
96 hr periods if measured concentrations are more than 150 mg/l. As 
they say, more study is needed.
There were additional studies conducted by the Texas A and M group on 
Carysfort reef but they, like the smearing of drill mud paste on live 
coral, remained in the grey literature category. David, thanks for 
stimulating me to dredge this stuff up (no pun intended).
      And finally I want all to know that as you read this, J. Harold 
Hudson will be on an airplane to Germany where on February 9th the 
University of Frankfurt will bestow upon him an honorary PhD. The 
degree is for pioneering work on the application of coral banding for 
determining coral health and environmental impacts of pollutants on 
coral reefs. Those who have followed his pioneering lead owe him a 
round of thinks. His continued devotion to reef restoration while 
working for the NOAA Florida Keys Marine Sanctuary since that early 
work has been exemplary. Gene 


No Rocks, No Water, No Ecosystem (EAS)
------------------------------------ -----------------------------------
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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