Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp, 1.19-148. 



External metabolites in the sea 



By C. E. Lucas 

 Marine Laboratory, Aberdeen 



With the exception of a hint or two before the turn of the century, by such prophets 

 as Brandt and Nathansohn, it was not until the inter-war period tiiat marine workers 

 began to turn their minds to the possible existence of more subtle ecological relation- 

 ships than those imposed on organisms by their inanimate environment and by 

 predators. It is relevant that Knorrich and Putter had postulated the direct food 

 value of dissolved organic food substances in the sea, although this view appeared to 

 be finally rejected by Krogh (1931); however, such possibilities are not the main 

 subject of this paper, although they may once again demand investigation. But those 

 who drew our attention once more to the other possible significance of dissolved 

 organic matter deserve our gratitude. Quite the most senior of those now living was 

 Henry Bigelow who said in his famous book Oceanography, among many other 

 stimulating things, " as yet we know little of the inter-relationships of different species 

 or groups of animals in the sea beyond the obvious fact that some prey on others, 

 but we may be certain that in many cases inter-relationships of less obvious sorts are 

 vital links in the animal economy " (Bigelow, 1931, p. 131, quoted by Russell, 1936). 

 Before many years elapsed, it seemed clear that he was right and we now know that 

 he was! For the volume in his honour, it is fitting to pay tribute to his foresight. 



It would not be proper on this occasion, however, to ignore the others: from 

 Johnstone, Scott and Chadwick (1924)* to Allee (193l)t and Hardy (1935):}:. 

 All were feeling towards the certainty of a new type of relationship in ecology, and 

 particularly marine ecology, for which there was then all too little evidence (although 

 it may now seem striking that it was around this very time, in 1929, that the late Sir 

 Alexander Fleming was making his first observations on the antibiotic influence o'i 

 Penicillium). It was the stimulus of such hints, and particularly that of working with 

 Hardy when he was evolving his idea of " animal exclusion ", that led Lucas to 

 gather an odd collection of references in support of a speculative theory of " non- 

 predatory " relationships — based on the release and biological influence of metabolites 

 ranging from " toxins to vitamins and hormones " (Lucas, 1938). 



This evidence ranged from the effects of external metabolites in the field of bacterio- 

 logy, through some of the " mass physiology " experiments of Allee's school, to the 



* " Also, we are pretty sure that the plankton communities influence each other — that there are 

 what we may call group symbioses on the great scale so that the kind of plankton which we may 

 expect to be present in a certain sea-area must depend, to some extent, on the kind o{ plankton which 

 was previously present." 



t " Once formed, aggregations of aquatic organisms condition the medium surrounding them by 

 the addition of secretions and excretions, the nature and biological effect of which form one of the 

 important problems of mass physiology." 



X Hardy postulated a " presumably chemical " basis for his theory of " animal exclusion ", and 

 also speculated upon the '" biological history " of waters, e.g. the changes which may occur in water 

 passing from regions of predominantly "free" phyto-plankton to regions of "■ imprisoned" phyto- 

 plankton. 



139 



