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Detritus is critical to the estuarine ecosystem because it is the main 
pathway by which energy flows from plant producers to animal con- 
sumers (fig. IV). It serves to store the energy for later use, to trans- 
port it to less rich areas of the system and as a buffer mechanism 
against lean periods. The marsh exports 45 percent of its net pro- 
duction, and most of this is transported in the form of detritus. I 
would like to emphasize this important fact of marsh export. A useful 
analogy would be that the marshes are the ‘wheat fields” that give 
sustenance to the ‘teeming cities’ of fish in the estuaries. In com- 
parison, a forest is also a balanced system but its total production is 
utilized in sito (there is no excess of material for export) and agri- 
cultural lands which are unbalanced, operate at a net loss, requiring the 
artificial replacement of nutrients. Although the nutritive value of 
detritus has been described, the actual pathways of utilization are 
not fully understood. Detritus may be reused or used partially by 
one organism and then passed on to another. For example, a crab 
may ingest large detrital particles, assimilate some of their compo- 
nents and then excrete a residue that is further utilized by snails or 
worms. 
Besides the instrumental role bacteria play in the formation of 
detritus, they are important in other respects. Because of their large 
numbers, their rapid rate of multiplication, and their intense bio- 
chemical activity, they have a pronounced effect on the chemical and 
biological conditions of their environment. As has been described they 
break down plant material into usuable components for animal con- 
sumption and they add to the nutritive value of detritus when ad- 
hering microbes are actually ingested. In addition, bacteria are re- 
sponsible for the remineralization of organic matter—thus completing 
the circuit by making nutrients again available for utilization by 
plants. Finally, some species of bacteria are able to synthesize vitamin 
By, which is also a valuable export of the salt marsh and 1s utilized 
by all of the animals that come to feed in the estuary. 
The salt marsh, discussed in abbreviated form above, is of vital 
importance to man and this can readily be seen when commercially 
important organisms and their relationships to salt marshes are 
studied. The coastal fishery has its beginnings in the marsh. It has 
been shown that at least 60 species of fishes are dependent on the 
estuarine-salt marsh ecosystem at some stage in their life cycle. Such 
species as flounder, menhaden, bluefish, anchovies, and striped bass, 
all spawn offshore but send their young up into the estuary where they 
attain most of their growth. Tidal creeks are actually “nurseries” for 
the juvenile of these species. 
Of economic importance is the fact that about 90 percent of the 
total harvest taken by commercial U.S. fishermen is dependent on the 
estuaries. In 1960, sport fishermen in New England landed 800 
million pounds of fish, worth over $60 million—500 million pounds of 
this catch consisted of species that depended directly on the energy 
excess produced in the salt marsh. The menhaden has been studied 
rather closely and McHugh estimates that an estuary can produce 
780 pounds per acre of this fish. Using shelled hybrid corn as a food 
source, man can produce 1,000 pounds per acre of poultry, 540 pounds 
per acre of pigs, and 270 pounds per acre of cattle. Menhaden reared 
naturally do not differ greatly in overall production from livestock 
reared by man’s efforts. In addition to the various fish that need the 
