[Coral-List] making little one out of big ones (John Ware) Issue 29

[Gene Shinn]

Thanks John for providing an opportunity to join in on this boring topic.

...Back in the stone age (1958) when I began helping Bob Ginsburg run 
his Florida Keys field trips it was common practice to break open a 
piece of dead coral at each dive stop and demonstrate to students the 
various boring organisms that make little ones out of big ones.  Bob 
had published on the various boring organisms in the 1950s. More than 
20 years later, following Hine and Risk (1974), Hudson (1977), 
determined  the long-term bioerosion rate of  the combined activities 
of 6 -species of boring sponges.   He did this by taking overlapping 
cores (in 1976) along the side of previously sampled core holes 
(1974) that had been drilled in dead heads at Hens and Chickens reef 
in the Florida Keys. This large inshore patch reef  had been killed 
during the cold-water outbreak of 1969-1970 (widely, and mistakenly, 
reported in popular media at that time as death by pollution). Hudson 
had originally cored both the living and the dead corals at Hens and 
Chickens  in 1974 as a way of determining the exact time of death. 
Several obvious internal stress bands, visible in x-radiographs of 
the cores from  all the heads, allowed direct measurement of skeleton 
removal from the dead heads since the time they died.  He found that 
between 1970 and 1974, 0.54 cm had been removed by borers and between 
1974 and 1976 bioerosion rate increased to an average annual rate of 
0.64 cm. The latter  rate  is essentially the annual growth rate of 
live Montastrea sp. A roughly 50/50 ratio of growth versus removal by 
bioerosion.  By extrapolation Hudson concluded that bioersoion can 
reduce a dead 1-m-high coral head  to 0- m  in 150 years (Hudson 
1977) and that does not include simultaneous chewing and boring 
around the base of the heads. How much might have also been removed 
by dissolution, indolithic algae, and parrot fish, was not known but 
it should be noted that sediment cover (produced by boring and biting 
organisms along with Halimeda ) smothers and prevents further 
bioerosion.   If this did not happen we would not see coral skeletons 
preserved in the fossil record. A fossil coral reef is generally 
about  50/50 reef builders and reef-derived sand. Surprisingly, the 
present-day Florida reef tract is composed mostly of lime sediment 
and most of that is derived from calcifying algae, not coral. Even 
the sediment pockets within individual coral reefs is principally 
composed of algal  grains, namely Halimeda. This was also true during 
the Pleistocene when coral reefs and algae  were forming what is now 
the Florida Keys and sea level was about 7 m higher than today.
      In the Hudson (1977) study, bioerosion increased in the time 
interval between the first and second coring episode so one might 
wonder if the increase had anything to do with increased nutrients? 
Alternatively, was it due to a lag effect? Does the surface need to 
be prepared by bacteria  before the boring critters can  get up to 
speed? We may never know.
      Another factor to throw into the discussion is sponge health. 
Repeated blights of unknown origin decimated the commercial sponge 
industry throughout the Caribbean and Gulf of Mexico in the 1930s and 
1940s. Algal blooms and red tides also killed sponges in Florida Bay 
in the late 1980s and early 1990s. The latter may be anthropogenic 
but the Caribbean-wide blights of the 1930s and 40s most likely were 
natural.  Being of the same Phylum, one might wonder if the boring 
sponges are subject to the same kinds of blights that have occurred 
simultaneously throughout the Caribbean? Could sponge blights, 
instead of nutrients, explain the waxing and waning of boring 
activity or is it just us people who worry about these things that 
are so boring? Gene

Hein, F. J. and Risk, M. J., 1975 Bioerosion of coral heads: inner 
patch reefs, Florida reef tract: Bull of Mar. Sci. 25 (1) p. 133-138.

Hudson, J. H.,  1977, Long-term bioerosion rates on a Florida reef: A 
new method, Proceeding, 3rd International Coral Reef Symposium. p. 
491-497

-- 


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---------------------------------- 
-----------------------------------