SECT. 2] BIO ASS AY OF TRACE SUBSTANCES 229 



Bernhard (1955) showed that development in Dendraster eggs is highly 

 sensitive to trace concentrations of heavy metals and Arnon (1958) has studied 

 trace-element requirements in algae. These two investigations suggest that 

 highly specific and sensitive bioassays for trace amounts of metallic ions might 

 also be practical. 



Another perspective is the application of bioassay techniques to such specific 

 problems in the ocean as bloom succession, sporadic plankton distribution and 

 ecological relationships. But there are other problems of interest, possibly 

 amenable to attack by these techniques. Some results obtained on the Zig Pac 

 cruise (Belser, unpublished work, 1959) suggest that it might be possible to 

 distinguish water-masses on the basis of their organic content, and to describe 

 the boundaries between them with some accuracy. In Fig. 1 are shown some 

 data from the Zig Pac cruise. The boundary between the warm and cold water- 

 masses is defined by use of animal indicator species. These data have been 

 found to correlate well with temperature-salinity studies of boundary condi- 

 tions. The data from the bioassay, with the exception of station M, correlate 

 quite well with the animal indicator data, and suggest that the bioassay will 

 provide still another valuable parameter in the study of oceanography. 



Since land drainage by rivers is often characterized by a high and rather 

 representative organic content (Jerlov, 1955), it might also be possible to 

 ascertain the fate of that water once it reaches the sea. Bioassays from a river 

 effluent out into the ocean would show rates and direction of flow and rate of 

 dilution. It might also be possible to assess the potential contribution of such 

 drainage to productivity. 



An extension of the bioassay technique which increases the sensitivity of 

 detection is that of bioauxanography. In cases where the unknown organic 

 materials can be separated by paper chromatography, the assay organisms may 

 be used to detect the position of specific fractions on the paper. This is accom- 

 plished by cutting strips from the chromatogram parallel to the direction of 

 solvent flow. These strips are placed on the surface of agar plates seeded with 

 the assay organisms. The portion of the paper which contains the substrate for 

 the assay organism will be surrounded by a zone of growth, thus indicating its 

 position. This technique has been used in studies of the vitamin content of 

 algae (Ericson and Carlson, 1953; Larson and Haug, 1959), and for various 

 specific trace organic substances from animal body fluids (Baker et al., 1959). 

 An excellent review of microbiological assays, describing equipment, sources of 

 organisms and application for general purposes has been published by Hutner 

 et al. (1958). In this paper are described some of the non-marine problems which 

 might conceivably be attacked by bioassay techniques. 



Although the bioassay technique is relatively new in its application to 

 oceanography, there is little doubt that it represents a potentially valuable tool. 

 Used in combination with chemical, physical and classical biological methods, 

 the bioassay may well extend our knowledge of the biochemical cycles in the 

 ocean. 



The author gratefully acknowledges support from the National Science 



