M— Continued 



metabolism— The process by which an orga- 

 nism builds and breaks down compounds 

 within the organism. See also anabolism 

 and catabolism. 



metagenesis — Alternation of generations; 

 the occurrence of an asexual stage fol- 

 lowed by a sexual stage in the life 

 history of an organism. 



metamorphosis— The process of changing 

 through stages from egg to adult. (1) 

 Complete: egg, larva, pupa, adult. (2) 

 Incomplete: egg, nymph, adult. 



microbiota— Small microscopic organisms. 

 Opposite of macrobiota. 



microclimate— The climate conditions in 

 small areas that, due to localized con- 

 ditions, are different from the general 

 climatic conditions in the area (e.g., 

 south-facing slope or under-rock habi- 

 tat). See also macroclimate. 



microfauna— Those animals equal to or less 

 than 0.5 millimeter in size. 



micronutrient— A nutrient needed in small 

 or trace amounts, as opposed to macro- 

 nutrient. 



microplankton— Plankton within size range 

 of 60 micrometers to 1 millimeter. 



mixed layer— A water layer mixed by wind, 

 wave, or thermal action. 



molt— In anthropods, the shedding of the 

 exoskeleton to allow for growth and 

 development. 



monocultural system— A system where one 

 species is maintained, usually artifically. 



monoecious— The production of sperm and 

 eggs by the same organism but not 

 necessarily self -fertilizing. 



monomictic lake— A lake with only one 

 overturn per year. There are two types: 

 (1) Warm— water never below 4°C, over- 

 turn in the winter; and (2) Cold— water 

 never above 4°C, overturn in the sum- 

 mer. 



mortality— Number of deaths in a given 

 time period. Usually expressed as deaths 

 per 1,000 population per year or per 

 generation. 



mutualism— A symbiotic relationship in 

 which both members benefit. Neither 

 can survive without the other. 



--N-- 



nannoplankton— Plankton in the size range 

 5 to 60 micrometers, defined as uncatch- 

 able in standard plankton nets. 



natality— See birthrate. 



natural selection— The differential perpet- 

 uation of genotypes, where selective 

 pressure favors one genotype over 

 another. 



nekton— Those aquatic animals able to 

 swim efficiently, and not mainly at the 

 mercy of currents. 



neritic— (1) Refers to waters over the Con- 

 tinental Shelf. (2) Pertaining to that part 

 of the Continental Shelf between the 

 low tide line and depths of 200 meters 

 including both bottom and overlying 

 waters. 



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