FISHERY BULLETIN: VOL. 70, NO. 3 



in progress at the Atlantic Estuarine Fisheries 

 Center will enable us to estimate the size ranges 

 for most reservoirs of manganese, iron, and zinc 

 in our local estuarine system. The major gaps in 

 our present knowledge lie in: 



1. Determining the relative amounts of dif- 

 ferent physico-chemical forms of an element or 

 radioisotope in natural waters, their relative sta- 

 bilities, and the ease of interconversion between 

 the various forms. 



2. Determining the relative biological availa- 

 bilities of these different physico-chemical forms 

 to various types of biota. 



3. Determining trophic structure of the entire 

 ecosystem. The , xo\e of microorganisms — as 

 sources of metallic elements to consumers in 

 detritus-based food chains, as producers of or- 

 ganic-metal complexes, and as remineralizers 

 of metals previously incorporated into plant or 

 animal tissues — is particularly poorly under- 

 stood. 



4. Determining feeding rates and assimilation 

 efficiencies for carbon and metallic elements at 

 each major trophic interaction. 



5. Determining biological retention of metallic 

 elements in the major organisms consumed by 

 man. 



6. Determining the interactions of variable 

 environmental parameters on reservoir size and 

 transfer rates at each step in the overall system. 



As further information becomes available, this 

 preliminary systems model will be refined and 

 tested as to its adequacy for describing the flux 

 of manganese, iron, and zinc in our local estua- 

 arine system. Maintenance of this sort of ho- 

 listic viewpoint toward ecological function and 

 continuous updating of existing conceptual mo- 

 dels will provide the most reliable basis for ra- 

 tional management of man's releases of toxic 

 heavy metals and radionuclides — or indeed, of 

 any contaminant additions to the environment. 



LITERATURE CITED 



Bache, C. a., W. H. Gutenmann, and D. J. Lisk. 



1971. Residues of total mercury and methylmerc- 

 uric salts in lake trout as a function of age. 

 Science (Wash., D.C.) 172:951-952. 



Baptist, J. P., and C. W. Lewis. 



1969. Transfer of 65Zn and siCr through an estu- 

 arine food chain. In D. J. Nelson and F. C. Evans 

 (editors). Symposium on Radioecology, p. 420-430. 

 USAEC CONF-670503. Oak Ridge, Tenn. 



Baptist, J. P., D. E. Hoss, and C. W. Lewis. 



1970. Retention of siCr, s^Fe, soCo, ssZn, s^Sr, 95Nb, 

 147 mjn and ^''I by the Atlantic croaker (Microp- 

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Barber, R. T., and J. H. Ryther. 



1969. Organic chelators: Factors affecting pri- 

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Chipman, W. a., T. R. Rice, and T. J. Price. 



1958. Uptake and accumulation of radioactive zinc 

 by marine plankton, fish, and shellfish. U.S. Fish 

 Wildl. Serv., Fish. Bull. 58:279-292. 



Cross, F. A., and J. H. Brooks. 



In press. Concentrations of Mn, Fe, and Zn in ju- 

 veniles of five estuarine-dependent fishes. In D. J. 

 Nelson (editor). Third National Symposium on 

 Radioecology. USAEC Oak Ridge, Tenn. 



Cross, F. A., T. W. Duke, and J. N. Willis. 



1970. Biogeochemistry of trace elements in a coast- 

 al plain estuary: Distribution of manganese, iron, 

 and zinc in sediments, water, and polychaetous 

 worms. Chesapeake Sci. 11:221-234. 



Cross, F. A., J. N. Willis, and J. P. Baptist. 



1971. Distribution of radioactive and stable zinc 

 in an experimental marine ecosystem. J. Fish. 

 Res. Board Can. 28:1783-1788. 



Duke, T. W., J. N. Willis, and T. J. Price. 



1966. Cycling of trace elements in the estuarine 



environment. I. Movement and distribution of 



zinc 65 and stable zinc in experimental ponds. 



Chesapeake Sci. 7:1-10. 



Duke, T. W., J. N. Willis, T. J. Price, and K. Fischler. 



1969. Influence of environmental factors on the 

 concentrations of •'^Zn by an experimental com- 

 munity. In D. J. Nelson and F. C. Evans (edi- 

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 USAEC CONF-670503. Oak Ridge, Tenn. 

 Duke, T. W., J. N. Willis, and D. A. Wolfe. 



1968. A technique for studying the exchange of 

 trace elements between estuarine sediments and 

 water. Limnol. Oceanogr. 13:541-545. 

 Epstein, E. 



1965. Mineral metabolism. In J. Bonner and J. E. 

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 Academic Press, N.Y, 

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1952. Iron assimilation by marine diatoms. Biol. 

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1963. The oceans as a chemical system. In M. N. 

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