Information Concept in Ecology 155 



The concentration of ash-free solids (Fig. 7) was observed to 

 increase markedly with depth. This variable may be equated to 

 community biomass since even the non-living detrital material 

 which it includes represents a source of energy to certain hetero- 

 trophic components of the living plankton. The inverse relationship 

 between the vertical distribution of these ash-free solids and that 

 of living cells is a consequence of the detrital rain from the zone 

 of production at the top of the water column, and also of the 

 upwelling of bottom materials. Since even dead organic material 

 of this type has an oxygen demand, a significant (though un- 

 specifiable) fraction of what was represented in Figure 6 as com- 

 munity "respiration" is a product of non-biological oxidations 

 attending decomposition. Since such oxidations cost the com- 

 munity biomass energy, it is proper that they be included in 

 determinations of energy loss. 



As in the case of ash-free seston, the vertical distribution of 

 total chlorophyll was different from that which would be antici- 

 pated on the basis of the cell-count data (Fig. 7). Chlorophyll 

 concentration increased gradually with depth. The explanation 

 is that large quantities of chlorophyll- and its degradation products 

 (many of which would be included in this assay) are associated 

 with non-living detritus (28, 29) and sediments (30, 31, 32). The 

 two curves of Figure 7 strengthen the conclusion that we are 

 dealing with a fairly well-mixed water mass since a certain amount 

 of upwelling is indicated. 



Let us now consider some of the photosynthetic characteristics 

 of the plankton community at various depths. 



Recall from the description of procedures that water samples 

 for the measurement of photosynthesis were collected at depths 

 of 2, 6 and 10 ft. and were resuspended so that data for all com- 

 binations of collection and suspension depths could be obtained. 

 The graphs in Figure 6 are for results from the particular com- 

 binations (2,2), (6,6) and (lO,10). In Figure 8, ail of the combina- 

 tions are graphed in 3-space with coordinates (collection depth, sus- 

 pension depth, mean photosynthesis). The surface depicted is 

 concave upward, slopes downward toward the viewer, and curves 

 markedly upward on the left. Consider, first, photosynthesis as 

 a function of suspension depth, by looking at the surface from back 



