FISHERY BULLETIN: VOL. 70, NO. 3 



zooplankton. Suspended particulate matter may 

 arise also from the ultimate flocculation and pre- 

 cipitation of dissolved ionic species, such as Fe 

 and Al, which are readily hydrated to form col- 

 loidal hydroxides at the pH of seawater (Riley 

 and Chester, 1971 ) . Other sources of suspended 

 particulate matter include feces excreted directly 

 into the water column by pelagic animals, cast- 

 off exuviae from zooplankton, and dead plank- 

 tonic organisms. 



Different dissolved chemical species in the 

 water undoubtedly represent discrete and signifi- 

 cant reservoirs in the cycling of elements. Or- 

 ganic metallic complexes or chelates may equili- 

 brate slowly with the ionic forms and have been 

 shown or suggested to have drastically different 

 availabilities to organisms. For example, EDTA 

 (ethylenediaminetetraacetic acid) reduced the 

 accumulation of ^^Fe by crabs (Panopeiis) , clams 

 (Me?'ce7?a?'/a) , and oysters (Crassostrea) (Rice, 

 1965). Goldberg (1952) demonstrated that the 

 marine diatom Asterionella japonica also could 

 utilize iron if particulate or colloidal but not 

 when complexed with citrate, ascorbate, or arti- 

 ficial humate. On the other hand, accumulation 

 of cobalamin by clams {Donax) was much en- 

 hanced over accumulation of ionic cobalt (Low- 

 man and Ting, in press) ; and it has been sug- 

 gested that natural organic chelators may en- 

 hance the growth of phytoplankton (Barber and 

 Ryther, 1969), thereby implying that organic 

 complexes might constitute an important avenue 

 for accumulation of metallic nutrients by marine 

 organisms. Unfortunately, technology for the 

 separation and identification of organic ligand- 

 metal complexes from natural waters is in 

 its early infancy, and one can only speculate 

 on the significance of the various chemical 

 forms present in estuarine waters. Regard- 

 less of the relative biological availabilities of 

 metals from different organic complexes or from 

 uncomplexed forms, the formation of soluble or- 

 ganic-metal complexes increases the holding ca- 

 pacity of estuarine water for a particular me- 

 tallic element. Soluble organic complexes there- 

 fore probably decrease the net adsorption of 

 metals onto sedimenting particulate materials, 

 thereby increasing the metals* susceptibility to 



export via tidal flushing. The nonliving element- 

 al reservoirs designated in Table 2 are thought to 

 be of greatest significance in determining the 

 distribution and flux of metallic elements in es- 

 tuaries. 



The estuarine biota consists of many species in 

 a complex and interwoven network of feeding 

 relationships. From a practical viewpoint, all 

 species cannot be considered major elemental res- 

 ervoirs for modeling purposes. One approach 

 would be to group species by trophic position and 

 consider each trophic level as a single reservoir. 

 Many species, however, are opportunistic feeders 

 with omnivorous habits which complicates their 

 ready assignment to a particular trophic level 

 and necessitates the use of fractional trophic 

 levels. In addition, some species of comparable 

 trophic position and abundances must be con- 

 sidered separately because one is desired as 

 human food and another not. For example, 

 oysters, clams, and scallops should be considered 

 separately from other filter-feeding bivalve mol- 

 luscs. Another example might be the primary 

 carnivores, flounders and skates, of which only 

 the flounder is harvested for human food. It is 

 more feasible to group species wherever possible 

 and consider individual species only where neces- 

 sary. Preliminary surveys of the estuarine flora 

 and fauna in the vicinity of Beaufort, N.C., sug- 

 gest that the organisms in Table 2 should be con- 

 sidered as separate reservoirs or components. 

 Some of the species are identified because of 

 their commercial importance; others only be- 

 cause of their abundance and probable signifi- 

 cance as forage. Organisms not identified to 

 species have been lumped arbitrarily into "oth- 

 er" categories according to their feeding habits 

 and trophic position. 



The reservoirs identified in Table 2 as being 

 "significant" or "important" in the cycling of 

 elements in estuaries obviously are not all of 

 equal importance. The list is probably incom- 

 plete, but at the same time may include some 

 unnecessary designations. Most of the reser- 

 voirs identified to species have been considered 

 in the development' of a static model of annual 

 energy flow in these estuaries (Williams and 



962 



