COMPARISON WITH OTHER AREAS 



359 



TIME SCALE INTEMPERATE REGIONS: 



SPRING EARLY SUMMER LATE SUMMER 



PHOSPHATES AND 

 PHYTOPLANKTON DECREASING - 



ZOOPLANKTON AWAY 

 FROM SURFACE IN 

 DAYLIGHT 



/S 



"H 0: 



ZOOPLANKTON NEAR 

 SURFACE IN DAYLIGHT 



PHOSPHATES RETURNED 

 TO WATER ON DECAY 



OF ZOOPLANKTON 



, SPn AJ - 

 SU«F AC g fiETU «^0 TO 



' N AUTUMN 



ANO WINTER -' 



space scale: 

 polar regions. 



TEMPERATE REGIONS... TROPICS 



PHOSPHATES AND 

 PHYTOPLANKTON DECREASING 



marked migration 

 of'zooplankton 

 from: surface in 

 daylight 



"*** 



% 



SPECIALIZED 



SURFACE 



FAUNA 



PHOSPHATE RETURNED 

 TO WATER ON DECAY 

 OF ZOOPLANKTON 



nutritive chains of animal organisms, carried in the ocean currents, conveying these 

 substances from the temperate regions of phytoplankton production to the tropical 

 zones of low nutritive content. Fig. 193 

 shows diagrammatically the two series of 

 events, phenomena which appear to be 

 the same, the one in a time and the other 

 in a space dimension. Each with a reduc- 

 tion of "free" phytoplankton shows a 

 change to a condition when animal plank- 

 ton may be found in abundance at the 

 surface in bright sunlight. In each we 

 must suppose that the nutritive substances 

 taken from the water by phytoplankton 

 are handed on in a chain of animal or- 

 ganisms shown in the diagram as ABC 

 and D, B feeding on A, C on B, D on C. 

 It is well known that when planktonic 

 animals die and sink the nutritive salts are 

 returned to the water of the lower layers 

 by the action of bacteria, to be brought 

 to the surface in temperate regions by the 

 water disturbances of autumn and winter, 

 or by upwelling, and in our other wider 

 example to be carried back towards the 

 Pole by the warm intermediate current. 



If this comparison between the events in space across the world from the polar 

 regions to the tropics and the events in time between spring and late summer in the 

 temperate regions is a correct one, then the chain of animal organisms ABCD ... in the 

 former case must be an exceedingly long one. The expression "free phytoplankton" 

 was used above because we must not overlook the role played by the symbiotic algae of 

 the Foraminifera (Globigerina) and the Radiolaria. It seems possible that these organisms 

 may play a much more important part in the economy of tropical seas than is usually 

 attributed to them, in that they may assist in prolonging the transference of nutritive 

 substances in the animal organisms over vast stretches of the ocean. If the suggested 

 hypothesis is correct, that phytoplankton creates an uncongenial environment, it is 

 possible that these animals, like the corals and many other animals which live in the 

 upper zones of the tropical seas and which have symbiotic algae, have by imprisoning the 

 phytoplankton been able to overcome the excluding influence by some counteracting 

 physiological process, and the imprisoned phytoplankton in turn are able to obtain from 

 their hosts the phosphates and other nutritive substances which are lacking in the 

 tropical waters. The possibility of skeleton formation being such a counteracting physio- 

 logical process has been mentioned on p. 335. The greater deposition of carbonate by 



46-2 



*1+T, 



£5 



*£Q l en ^« TO 



' N "^MEDIATE LAYER - 



Fig. 193. 



