9. BIOASSAY OF TRACE SUBSTANCES 



W. L. Belser 



1. Introduction 



One of the truly fascinating problems in the study of the oceans is the fact 

 that animal and plant life is not everywhere abundant. Ancient maps show sea 

 monsters on every quarter, with fish leaping all over the surface of the ocean. 

 Today, we know that this is not a true picture. Some areas of the ocean are 

 barren of life (aquatic deserts) ; others possess a profusion of plant and animal 

 species. 



Redfield, Ketchum and Richards in Chapter 2 have approached the 

 problem of oceanic fertility, dealing with two of the major constituents of sea- 

 water — phosphates and nitrates. They point out that these two chemicals 

 profoundly influence the biology of the sea, and, conversely, that the biology 

 of the sea has a marked influence upon the concentrations of phosphate and 

 nitrate. It would be a tidy solution if we were able to ascribe all biological 

 variability to these two constituents. The observation that adjacent areas of 

 very similar chemical composition in respect to phosphate and nitrate may vary 

 from a dense plankton bloom to veiy few organisms, suggests, however, that 

 there is not a simple relationship between nitrogen-phosphorus concentrations 

 and biological activity. The sporadic distribution of living organisms presents 

 us with evidence that the ocean is not a uniform environment for biological 

 activity, yet the two major constituents of sea-water, which are known to be 

 involved closely with marine life, do not seem to be the limiting factors in all 

 cases. We are thus presented with the problem that marine organisms can 

 detect differences in the physical and chemical make-up of sea-water which 

 we have not properly identified, and that, in our search for some of the factors 

 responsible for these differences, we have detected some substances whose role 

 in the biochemistry of the seas cannot yet be understood. 



Interest in microconstituents of sea-water possessing biological activity 

 stems from a publication by Putter (1907), but gained its greatest impetus as a 

 result of two subsequent papers by Lucas (1947, 1955). These papers drew to- 

 gether a considerable body of evidence dealing with the effects of extracellular 

 and extraorganismal substances upon the life and death of those particular 

 organisms and their neighbors. Most of the evidence favored rather small 

 molecules of organic composition of varying degrees of complexity. Thus we 

 can have an amino acid or vitamin functioning as a regulator in a physiological 

 process, or as an essential nutrient. There are innumerable instances cited in 

 the literature (see Lucas, 1947, for a review) implicating soluble extracellular 

 organic materials in feeding, homing, reproductive and other physiological 

 responses. Lucas has applied the name "ectocrine" to these substances. Sig- 

 nificantly, these subtle differences in sea-water were in each case observed 

 because the organisms could detect them. A striking case in point arises from 

 the work of D. P. Wilson (1954, 1958) in which he carefully checked the physical 



[MS received August, 1960] 220 



