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A key question in this ecosystem affected daily by over 85 million people could be " Is hypoxia a natural phenomenon ? " . ( 16 ) The large numbers of enclosed areas , in many cases with shallow sills that restrict the exchange of bottom water and often in combination with large irregular changes in salinity , might mean that hypoxia has always been present in the coastal zone .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Anatomy 
Text: {0} 
Answer:
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