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High-Nutrient, low-chlorophyll
HNLC stands for "high-nutrient, low-chlorophyll" - a term used in marine ecology to describe areas of the ocean where the number of phytoplankton (standing stock) are low and fairly constant in spite of high macro-nutrient concentrations (nitrate, phosphate, silicic acid). In general, some essential inorganic substances, like nitrate, may be present in oceanic waters in concentrations low enough to be limiting to plant production, but in HNLC regions the level of nitrate is never significantly depleted.〔Lalli, C.M. and Parsons, T.R.,2004, Biological Oceanography: An Introduction, 2nd Ed., Elsevier Butterworth Heinemann, Burlington, MA, p. 55.〕〔Pitchford, J.W. and Brindley, J. (1999) Iron limitation, grazing pressure and oceanic high-nutrient-low chlorophyll (HNLC) regions. Journal of Plankton Research, 21(3), 525-547.〕 Instead, these regions are limited by low concentrations of metabolizable iron.〔 There are two popular explanations for the existence of HNLC regions: the iron hypothesis and the ‘grazing control hypothesis'. HNLC regions cover 20% of the world’s oceans in three major areas: equatorial Pacific Ocean, subarctic Pacific Ocean and the Southern Ocean.〔〔
==Iron hypothesis==
The iron hypothesis proposes that a lack of iron in the ecosystem prevents phytoplankton from achieving an algal bloom.〔 Iron is necessary for nitrogen fixation which is required for the production of amino acids.〔〔Miller, C.B., 2008, Biological Oceanography, Blackwell Publishing, Malden, MA, p. 64-65.〕 This iron limitation inhibits the growth of larger phytoplankton, such as diatoms. Instead, HNLC regions are characterized by small phytoplankton flagellates which can take up iron at lower concentrations due to greater surface area to volume ratios.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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