I-A-10 



Bel lis, V. 1974. Medium salinity plankton systems. Pages 358-396 i_n_ 

 H.T. Odum, B.J. Copeland, and E.A. McMahan, eds., Coastal ecological 

 systems of the United States, Vol. 2. The Conservation Foundation, 

 Washington, D.C. 



This article presents a discussion of the "middle estuary." According 

 to the author, although the precise physical limits of this part of 

 an estuary are difficult to define, an arbitrary working definition 

 has been accepted by many persons in the field: the characteristics 

 of the middle estuary correspond most closely with portions of the 

 estuary having average salinities between 5-18 ppt. The middle estuary 

 is important because the greatest area of many North American estuaries 

 is of this type, and it is this portion which provides primary support 

 for certain fisheries (e.g., blue crab and oyster). In the United 

 States all of the east coast estuaries seem to have significant middle 

 salinity regions. 



Four examples of middle estuaries are given: Chesapeake Bay; Yaquina 

 Estuary, Oregon; San Francisco Bay system, and Galveston Bay. Middle 

 estuaries are discussed in terms of boundaries of the system, system 

 components, annual plankton periodicity, vertical distribution, system 

 dynamics, and geographical variations. 



One general characteristic of plankton organisms of the middle estuary 

 is that, while they may be volumetrically abundant, they tend to be 

 limited with respect to species variety. 



Plankton organisms form the dominant biomass of the middle estuary and 

 constitute the base of its food web. Photosynthetic production by 

 the phytoplankton serves as a direct source of biotrophic energy inflow. 

 A less obvious, but under some conditions equally significant, energy 

 input derives from import into the system of dissolved and particulate 

 organic matter. 



North Carolina's sounds constitute the largest estuarine system along 

 the Atlantic coast. Most of this vast system is of the medium salinity, 

 plankton-based type and as such functions as a nursery or temporary 

 home for migrating species of commercial importance. Shrimp, striped 

 bass, and menhaden are all estuarine-dependent species. In estuarine 

 systems such as this, efficiency of energy transfer between plant and 

 animal is greater than in most land environments. This is because the 

 producer components of the food web are primarily diatoms. (B.W.) 



Keywords: estuaries, plankton, biomass, food web, energy flow, phyto- 

 plankton, U.S. coastal regions 



