160 Information Storage and Neural Control 



the 2 — 10 ft. and 6 — 10 ft. means could not be distinguished. There- 

 fore, the tendency toward increased chlorophyll efficiency with 

 depth of collection cannot be formally accepted as a generalization. 

 We may accept it on intuitive grounds, however, noting the high 

 likelihood for a Type II (35) biometrical error due to small sample 

 size, i.e., an error such that the null hypothesis is accepted when 

 in fact it is false. 



Although physiological mechanisms {e.g., photoinhibition) are 

 doubtlessly involved in the observed increase of chlorophyll 

 efficiency with depth, ecological factors are also implicated. One 

 of the striking features about the vertical organization of summer 

 estuarine plankton communities is variability in species com- 

 position and in cell concentrations. The numerical stratification 

 of the York River phytoplankton has already been described 

 (Fig. 4). Table I is provided to illustrate the nature of species 

 changes with depth. It is a list of phytoplankton species and their 

 concentrations obtained from the third experiment (July 6) of the 

 series under consideration. There is nothing especially atypical 

 about this particular list; it is fairly representative. 



The table shows that two flagellates (in decreasing order of 

 importance: Massartia, Chilojrtorms) were dominant at the surface. 

 Two feet below, three species dominated in a diff'erent order of 

 abundance {Alassartio, Gjrodimum, Chilomonas). These forms are 

 all highly motile; Massartia and Gyrodinium are dinoflagellates, 

 Chilomonas is a yellow-green flagellate. Both of these groups typically 

 photosynthesize at maximal rates under conditions of high light 

 intensity (36). At 6 ft. the surface forms were no longer of sig- 

 nificance (dominants being Eutreptia, Gyrodinium), and at 10 ft. 

 they were entirely absent (dominants: Eutrepfia, Pyramimonas, 

 Leplocylindricus) . Eutreptia is a euglenoid, Pyramimonas a flagellated 

 green alga, and Leplocylindricus an immotile diatom. The latter 

 two groups, in estuaries, are generally adapted to photosynthesize 

 maximally under conditions of low or medium illumination (36). 



It would seem from these few general observations that main- 

 tenance of a suitable vertical diversity structure might constitute 

 a significant segment of community strategy in implementing the 

 goal of biomass maximization. That a very definite vertical 

 diversity pattern is maintained in summer is illustrated in Figure 1 1 



