grass. Size distribution by weight was as follows: 1 percent coarse detritus 



(defined as that retained by a No. 6 net - 74 meshes per inch; 0.239mm 



per aperture); 4 percent fine detritus (defined as that strained by 



a No. 25 net - 200 meshes per inch; 0.064mm per aperture); 95 percent 



nanno detritus (defined as smallest particles that pass nets Nos. 6 



and 25, but filtered by a membrane filter of 0.45 micron porosity). 



Calculations based on measurements taken through the tidal cycle 



in the autumn and winter of 1964 revealed an estimated net export of 



186 kg and 31 kg (averages of 3 measurements) of organic matter for 



spring and neap tides, respectively, from the 10-25 hectare marsh area 



in one tidal cycle. Oxygen consumption (BOD) per gram is more than 



three times as great in nanno detritus as compared with coarse detritus, 



indicating increasing microbial activity with age. The small suspended 



particles are 70-80 percent ash, but the organic portion is rich in 



protein, up to 24 percent on an ash-free basis as compared with 10 



percent in living grass and only 6 percent in the dead grass as it 



enters the water. Thus, the bacteria-rich detritus may be a better 



food source for the detritus consumers of the salt marsh-estuaries 



than the Spartina tissue that forms the original base for most of the 



particulate matter, provided the digestive tracts of detritus-feeding 



animals are adapted to handle large amount of undigestible mud and other 



ash components. Semi-qualitative estimations of stomach contents of 



marsh, estuarine, and coastal animals revealed the frequent occurrence 



(up to 50 percent of total stomach content) of organic detritus 



(mostly of Spartina origin) ; to what extent detritus present in the 



digestive tract is assimilated remains to be determined. The role 



of organic detritus as a major source of food for consumer species is 



reviewed and its ecological significance discussed, (A. A.) 



Keywords: detritus, Spartina alterni flora , salt marsh, estuaries, Georgia 



III-B-3 



Odum, E.P., and A. A. de la Cruz. 1967. Particulate organic detritus in 



a Georgia salt marsh-estuarine ecosystem. Pages 383-388 j[n G.H. Lauff, ed.. 

 Estuaries. American Association for the Advancement of Science, Washington, 

 D.C. 



Estuaries in Georgia dominated by Spartina alterni flora marshes have 

 organic detritus as the chief link between primary and secondary 

 productivity, since only a small portion of the net production of the 

 marsh grass is grazed while it is living. Seven aspects of detritus 

 are being studied at the University of Georgia Marine Institute at 

 Sapelo Island: 1) the seasonal picture of the standing crop of detritus 

 in water; 2) size distribution and composition of detritus particles; 

 3) tidal transport of detritus in and out of a 10-hectare marsh area 

 drained by a single small creek; 4) origin of the particles; 5) decomposition 

 of marsh grass in nylon litter bags; 6) nutritive values of different 

 age and size components; and 7) metabolism of detritus particles. 



99 



