MARINE BACTERIA AND THEIR RÔLE IN THE CYCLE OF LIFE IN THE SEA I. DECOMPOSITION OF MARINE PLANT AND ANIMAL RESIDUES BY BACTERIA

The synthesis of organic matter in the sea through the agency of the chlorophyll-bearing plants, ranging from the smallest diatoms to the largest algae, consists in the assimilation of the carbon as CO2, of the nitrogen as nitrate, and probably to a lesser extent as ammonia and nitrite, of the phosphorus as phosphate, and of other elements in lower concentrations. Before these elements can be returned to circulation, after the plants as well as the animals which fed partly upon them die, the complex organic substances have to be decomposed through the agency of bacteria. If one is to judge by analogy with the decomposition processes which take place on land, the liberation of the elements in a mineralized form does not represent a simple process, but rather a chain of processes. The rate of liberation of the elements by bacterial action depends primarily upon the chemical composition of the materials undergoing decomposition and upon the organisms active in the decomposition processes. The following investigations were undertaken for the purpose of determining to what extent the chemical composition of marine residues of plant and animal origin influences the rate of their decomposition by marine bacteria and the rate of liberation of the important elements, especially nitrogen, in. an available form. It was further essential to obtain light upon the mechanism of decomposition of some of the chemical constituents of the marine residues by specific members of the bacterial population of the sea. These investigations can be classified, therefore, under three distinct headings, namely: (1) the chemical composition of marine zo6plankton and of certain marine algae, (2) the decomposition of the plankton and algal material in sea water and in marine