Rôle of Bacteria in Decomposition of Plant and Animal Residues in the Ocean

Abstract

A study has been made of the decomposition of marine zoöplankton and of certain marine algae by bacteria in sea water and in marine mud. The formation of carbon dioxide and the liberation of nitrogen in the form of ammonia were used as measures of the rate of decomposition. It was found that the chemical nature of the material has a very important influence upon the rapidity and nature of its decomposition.

Zoöplankton, consisting largely of copepods, and containing 7.9% total N on a dry basis, was found to decompose very rapidly, both in the water and in the mud. Nearly one-third of the total C was liberated as CO₂ within 19 days' incubation, while a large part of the N was liberated as ammonia. A marked difference, however, was observed in the case of the medium in which the decomposition took place, namely, although the amount of N liberated was about the same in the water and in the mud, viz., 40.3 and 38.5 mg., a considerably greater amount of CO₂ was evolved in the mud than in the water, viz., 101 vs. 64 mg., above controls. This difference may be due to the fact that while the nitrogenous constituents of the zoöplankton decompose alike in water and in mud, some of the nitrogen-poor or non-nitrogenous complexes are decomposed more rapidly in mud than in water, probably due to the presence in mud of specific bacteria capable of attacking them.

For the decomposition of the algal material, Ulva lactuca and Fucus vesiculosus were employed. The decomposition of these substances, also, was quite different in water and in mud media; in Ulva, which contained 1.67% N in the total dry material, there was as much decomposition in water as in mud medium, as shown by the CO₂ liberated, viz., 83.4 and 101.8 mg. C. This was accompanied by the accumulation of small amounts of ammonia, viz., 5.2 and 4.1 mg., respectively, above controls.