ISAACS: FOOD WEBS AND "POLLUTANT ANALOGUES" 



an unstructured food web in the Gulf of Cali- 

 fornia in explanation of Young's findings on pre- 

 daceous fish leads to reasonable estimates of the 

 coefficient of conversion of food. 



PELAGIC VERSUS SHALLOW WATER 

 POPULATIONS 



Other variations or testable conclusions or 

 manipulations of these equations can be under- 

 taken. For example, we can derive the relative 

 biomass of two similar environments where, in 

 one, the recoverable matter approaches zero. 

 These might be a near-surface population ovej 

 deep water where Ks-^ because of rapid sink- 

 ing of inert particles compared with a similar 

 population over shallow water where K3 could 

 have any of the values shown in the table above. 



From equation (4) 



Mt' pelagic 

 Mt shallow 



X (1 - 



Mo pelagic 

 Mo shallow 



K. 



fc)' 



(13) 



For the range of values found in the Gulf 



K3 = 0.0 

 Ks = 0.1 

 Ks = 0.2 

 Ks = 0.3 

 K3 = 0.4 



Ki = 0.18 

 Ki = 0.20 

 Ki = 0.19 

 Ki = 0.18 

 Ki = 0.16 



(1- 



K: 



k' 



= 1.00 

 = 0.88 

 = 0.75 

 = 0.62 

 = 0.52 



THE MULLET ANOMALY 



The high Cs/K ratio of the mullet is difficult 

 to explain. It is generally thought that the mul- 

 let is largely herbivorous. Three possible factors 

 may give rise to the anomalous levels: First, the 

 mullet in the Gulf of California may ingest far 

 more organisms with the detrital material than 

 is generally supposed, and these organisms may 

 be part of a microscopic multistep food web 

 that generates a high Cs/K ratio. No such effect 

 was apparent in the Salton Sea, however, pos- 

 sibly because of the paucity and simplicity of 

 invertebrate infauna in the detrital mat. Sec- 

 ondly, some members of the detrital community 



in the Gulf may take up inorganic cesium from 

 the sediment, unlike those of the Salton Sea. 

 Third, the high fat level of the mullet results in 

 their possessing a caloric level, as related to 

 organic material, that is 1.6 that of the other 

 fish. This argues that it might be more signifi- 

 cant to normalize cesium to calories than to dry 

 organic weight, since more food intake (and 

 hence more cesium) possibly is required for a 

 given increment of growth in a fish with high fat 

 content, with the potassium better normalized to 

 fat free dry weight. This latter assumption 

 would bring the Cs/K ratio in the mullet into the 

 lower ranges of that in predaceous fish. 



Pursuing this latter possibility, the adjusted 

 Cs/K ratio for Gulf mullet can be set at about 10, 

 and considering that the composition of the det- 

 rital feeding creatures (Md) should be [from 

 food represented by equation (5)] 



then the Cs/K ratio should be 



(14) 



Mdc 



KicK. 



3c 



l-{Krc-{^Kzo)_ ^ ^0^^ 



K\jKzf 



(15) 



Substituting equations (8) and (9), as before, 

 this becomes 



K, = 1 -^ K^ 



(16) 



which is within the range of values for these con- 

 stants previously derived (e.g., Ks = 0.30, Ki = 

 0.18). In simultaneous solutions of equations 

 (12) and (16) values of Ks are extremely sen- 

 sitive to the values of concentration. The values 

 of Ki, however, are essentially stable. 



CONCENTRATION FACTORS 



It should be noted in this discussion that the 

 high concentration of cesium in the mullet may 

 be a specific case of a more general principle, 

 which is that the concentration factor (/c) of a 

 trace substance in a single step may be inversely 



1057 



