Information Concept in Ecology 165 



reduced at least until a point of no further loss (zero return) is 

 reached. Let us examine the behavior of the York plankton in 

 respect to this proposition. Referring to Figure 6, mean photo- 

 synthesis is observed to exceed mean respiration in the upper 

 water column {pir'~^ < 1) but not in the lower (ptt"^' > 1)- This 

 relationship is so typical in aquatic communities that the depth 

 at which the photosynthesis and respiration curves cross (ptt"^ = 1) 

 is a standard variable — the compensation depth. The mean depth 

 of compensation at the York sampling station during the summer 

 of 1960 was 6.5 ft.; this level is denoted by broken lines in Figures 

 3-7 and in Figure 1 1 . When phytoplankters drift beneath the 

 instantaneous compensation depth they experience, on the average, 

 a shift fi'om positive to negative energy balance. If a net positive 

 balance is to be achieved for the whole water columii it is necessary 

 that the community reduce energy losses in the lower part of the 

 column. This implies, by the mathematical nature of the cost 

 variable, increasing the rate of photosynthesis and /or depressing 

 the rate of respiration. Community behavior in accordance with 

 tlie former imperative has already been described as dark-adap- 

 tability. We consider now the attenuation of respiration. 



The data which have been presented indicate that althougli 

 photosynthetic capacity of the plankters was irreversibly (in 24 

 hours) less at the 6 and 10 ft. levels than at 2 ft. (Fig. 9), vigorous 

 respiration equivalent to that of surface populations persisted 

 down to 10 ft. (Fig. 6). Below 10 ft., however, oxygen uptake was 

 sharply reduced. The extent of actual metabolic failure must be 

 even gi^eater than indicated by Figure 6 since the concentration 

 of oxidizable detritus increased with depth (Fig. 7) producing a 

 continually increasing oxygen demand (reflected in the oxygen 

 curve of Fig. 3). This underscores the conclusion that metabolism 

 is sharply curtailed soon after the organisms drift beneath the 

 compensation depth. This phenomenon constitutes a pei'fect 

 response on the part of tlie community to the converse marginal 

 profitability principle, and is an example of ''beneficial death" (24) 

 at the community level. Beneficial death is u.sually thought of in 

 connection with individuals {e.g., dead cells forming" the matrix 

 of a functional tissue, as in plant xylem or some insect wings) or 

 populations {e.g., annual plants, some social insect castes, genetic 



