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OBLIGATE 



Limited to one mode of life or action. (See 

 Facultative) 



OCEANIC ZONE 



The region of open ocean beyond the continental 

 shelf. 



OLIGOTROPHY LAKES 



OMNIVOROUS 



OPTIMUM LEVEL 



ORGANISM 



OSMOREGULATION 



OVERTURN 

 (Turnover) 



Deep lakes which have a low supply of nutrients, 

 thus they support very little organic production . 

 Dissolved oxygen is present at or near saturation 

 throughout the lake during all seasons of the 

 year. (See Eutrophic Lakes) 



Feeding on both plant and animal tissue. (See 

 Herbivorous. Carnivorous) 



The most suitable degree of an environmental 

 factor for the full development of the organism 

 concerned. (See Tolerance Range) 



Any living individual. 



The adjustment in the osmotic concentration of 

 solutes in body fluids in organisms to 

 environmental conditions; e.g., when salmon 

 migrate from salt to freshwater. 



The period of mixing, by top to bottom circulation, 

 of previously stratified water masses . This 

 phenomenon may occur in spring and/or fall; the 

 result is a uniformity of physical and chemical 

 properties of the water at all depths. (See 

 Thermal Stratification , Chemical Stratification , 

 Spring Overturn , Fall Overturn) 



