[Coral-List] density of coral skeletons

dbucher dbucher at scu.edu.au
Thu Feb 9 18:40:49 EST 2006

Hi Marah,

Try the following reference for a discussion of Archimedian methods  
for determining density of bleached coral skeletons. The important  
distinction is whether you want bulk density/porosity or the specific  
gravity of the mineral matrix (microdensity). We recommended the use  
of acetone to penetrate the small pore spaces as the surface tension  
in water is too great to remove all gas bubbles. We accelerated the  
process by using a vacuum pump and a bell-jar to lower the pressure.  
Without the vacuum pump overnight soaking was not long enough - you  
need several days at least for porous skeletons. The acetone- 
saturated skeleton was then soaked in several changes of water.  
Acetone has the added advantage of dissolving residual organic matter  
(waxes, oils etc) left behind by the bleaching process. Buoyant weigh  
the saturated skeleton, dry it, coat it with a thin layer of parafin  
wax and buoyant weigh it again - if you accurately measure the  
specific density of the water in the weighing apparatus you can  
calculate the coral's total enclosed volume (matrix plus pore  
spaces), its dry weight and the volume of the matrix alone.

It's not the most exciting thing you will ever do, but it worked for us.

Bucher, D., Harriott, V. and Roberts, L. 1998 Skeletal bulk density,  
micro-density and porosity of acroporid corals. Journal of  
Experimental Marine Biology and Ecology.  228(1)117-135.

It's not the most exciting thing you will ever do, but it worked for  
us. See my small contribution to the next reference for an  
application of this method.

K. Koop, D. Booth, A. Broadbent, J. Brodie, D. Bucher, D. Capone, J.  
Coll, W. Dennison, M. Erdmann, P. Harrison, O. Hoegh-Guldberg, P.  
Hutchings, G.B. Jones, A.W.D. Larkum, J. O'Neil, A. Steven, E.  
Tentori, S. Ward, J. Williamson, D. Yellowlees  2001  ENCORE: The  
effect of nutrient enrichment on coral reefs: Synthesis of results  
and conclusions. Marine Pollution Bulletin 42(2):91-120.

Cheers, Danny

Dr Daniel Bucher
Lecturer, Marine Biology and Fisheries
School Director of Postgraduate Studies and Research
School of Environmental Science and Management
Southern Cross University
PO Box 157 Lismore, NSW 2480

Ph: 02 6620 3665
Fax: 02 6621 2669
Mobile: 0414 864085

 >Date: Wed, 8 Feb 2006 12:10:53 -0500
 >From: Marah Newman <mjnewman at ucsd.edu>
 >Subject: [Coral-List] density of coral skeletons
 >To: coral-list at coral.aoml.noaa.gov
 >Hi All,
 >I have several bleached coral skeletons and I need to calculate
 >skeleton density.  I have looked at several papers that detail...snip

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