and Burkholder, Limnology and Oceanography, _1, 202, 1956; Starr, Ecology, 

 37, 658, 1956). 



More recent studies on B vitamins in Bahia Fosforescente, Puerto Rico, 

 show values as follows in mulgra. of dried mud: ^\2t 280; biotin, 7; and 

 Bi, 73, or a ratio of about 40:1:10. Calculated ratios for half maximum growth 

 of vitamin-requiring microorganisms would be about 1:1:800, expressed in 

 weight of Bj2' biotin: Bi. Vitamin B12 appears to be present in relative ex- 

 cess, while thiamine may be a limiting factor for growth of some benthic pop- 

 ulations. Data obtained for ten segments of a mud core taken from the Bahia 

 suggest that these B vitamins may decrease steadily with increasing depth and 

 age of the sediments. Of the total 3^2 activity in muds, assayed with a mutant 

 strain of E. coli, from 7 to 29 percent appeared to be cyanocobalamine, as in- 

 dicated by Ochromonas determinations. The ratio of Bio in suspended solids 

 to B|2 i"^ solution was found to be about 2. 5 in the waters of Bahia Fosforescente, 

 Assays showed that B]^2 ^^ contributed from land drainage and also is produced 

 in shallow marine waters at significant physiological levels. 



The ecological relationships among organisms is oftentimes regulated by 

 chemical factors. One of the new aspects of this general problem is the role 

 of antibiotics in nature (Brian, Symposium on Microbial Ecology, Soc. Gen. 

 Microbiol., Cambridge U. Press, 1957). Our recent studies on antibiotic 

 substances in marine organisms have revealed interesting antimicrobial prop- 

 erties of gorgonian corals collected from reefs located off the southern coast 

 of Puerto Rico. Sea whips, sea fans and plexaurid corals were inhibitory to 

 many bacteria. The sea whip, Antillogorgia turgida, was especially striking 

 in its action against numerous marine bacteria. Micrococcus aureus, Clostrid- 

 ium feseri , and others. The active principle appears not to be located in the 

 brown core of horny corals, but is present in the outer cortex. Little or no 

 antimicrobial activity could be detected in species of stony corals that were 

 tested. These data suggest that antibiotics may have importance, and deserve 

 further consideration, in marine ecology. 



DISCUSSION 



Davis: I would like to make a few comments about soft coral and 



Thalassia and ask the speaker some questions about it. The 

 Florida coast has shallow waters and probably amounts to 500 

 miles of coral reef tract. There is 187 miles above Tortugas. 

 I would imagine that you might have to modify some of that be- 

 cause the Thalassia colonies are fewer down in your part of the 

 country but as you progress northward you get Cymodocea and 

 other things. I would question making that a separate type 

 although from a plant ecological point of view that may be safer. 



Burkholder: Have you ever seen them down there in the islands ? 

 Davis: Yes. I have been on Andros too. Thalassia covers the whole 



72 



