The dry weights of standing crops of turtle grass (whole plants of 

 Thalassia ), measured in February, 1958, in shallow waters of Puerto Rico, 

 range in tons per acre, from 3. 1 to 3Z.9. Production of Spartina at Sapelo 

 Island, Ga. , has been stated by E. Odum to go as high as 9 tons per acre. In 

 Puerto Rican waters, the green alga, Halimeda, showed values up to 43.3 tons 

 per acre; much of this weight is CaCO> An influence of substrate on the root- 

 rhizome to leaf ratio in Thalassia appears to be significant. The RR/L ratio 

 was 7.3 in coarse Halimeda sand, 4.7 in mud and sand, and 3.0 in fine mud. 

 The nutritive content of Spartina has been found to be about like that of Coastal 

 Bermuda grass (Burkholder, Bull. Torrey Bot. Club, 83, 3Z7, 1956). Spartina 



obviously provides carbohydrates, amino acids, vitamins, etc., for the marsh 

 and adjacent waters. Studies on decomposition of Spartina in wooden crates 

 showed 90 percent loss of dry matter by bacterial and mechanical means in the 

 course of a year (Burkholder and Bornside, Bull. Torrey Bot. Club, 84,366, 

 1957). In laboratory experiments, it was found that about 20 percent of ex- 

 tracted solubles from Spartina could be rapidly converted to bacterial dry mat- 

 ter. This means that about 11 percent of the annual crop of soluble materials 

 in the leaves may go into bacterial matter. The numerous bacteria living in 

 the marsh mud at Sapelo generally respond to addition of N-Z case or Spartina 

 extracts. This may be explained by the special amino acid requirements of the 

 marine bacteria, which we have found to respond well to a mixture of alanine, 

 glutamic and aspartic acids. 



Studies on the use of Thalassia by marine microbes indicate a similar 

 behaviour of bacteria present in shallow waters of Puerto Rico. Studies on 

 quantitative distribution of marine bacteria at different stations, in an area 

 covered by Thalassia near Isla Magueyes, showed the following numbers of 

 organisms per milliliter: blue surface water outside the grass bed, 627; water 

 in agitated Thalassia bed, 192,000; mud in Thalassia bed, 3,700,000; Thalassia 

 leaves ground in mortar, 15, 104, 000 per gram of grass . Out of 35 cultures of 

 bacteria tested, 10 grew very well, and 18 fairly well, on extracts of Thalassia 

 in sea water. Conversion of organic solubles from Thalassia to bacterial dry 

 matter ranged from 13.0 to 22.5 percent. As was the case with bacteria in the 

 Sapelo marshes, growth of bacteria isolated fromi Puerto Rican waters was 

 greatly stimulated by N-Z case or by Thalassia extracts, and to some extent 

 by dextrose, but not by additions of mud extract, or phosphate and ammonium 

 nitrate. In our recent laboratory experiments, bacteria growing on turtle 

 grass always gave rise to large populations of ciliated protozoa. Although there 

 is some direct consumption of turtle grass by certain animals, it appears that 

 a general scheme for the use of Thalassia in shallow tropical waters would be 

 something like the following: 



bacteria 

 Thalassia » and >ciliates — >microfauna — >macrofauna. 



detritus 



In view of the need for B vitamins by certain green flagellates, diatoms 

 and photosynthetic marine bacteria, it is important to learn more about the 

 distribution of these compounds in the sea. Studies on vitamin Bl2 in muds 

 and suspended matter of the Sapelo region have been published (Burkholder 



71 



