1-7 Pelagic Food Webs

1-7 Pelagic Food Webs - Pelagic Food Webs Topic 9 Chapter 2...

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Pelagic Food Webs Topic 9 Chapter 2 Chapter 11, pages 503-506
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Pelagic Food Webs Consider phytos, zoops and nekton together First, examine differences in primary productivity throughout the ocean and then how this influences nekton (including fisheries species)
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Definitions: 1. Standing crop (= biomass) = g C/m 3 for phytos, measured by satellite imagery or chemically by Chl a relatively easy to measure 2. Primary productivity = g C/m 3 /y, a rate an amount of photosynthesis (or production of carbohydrates) per time difficult to measure
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Methods to measure 1 o : 1) Light/dark bottle : Measure oxygen change in sealed bottles suspended in seawater Seawater added Some bottles are exposed to light Some darkened usually for 24 h Light bottle Dark bottle
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Light/dark bottle: In the light bottle, algae photosynthesize and respire [P + R] oxygen increases when P > R measures net production In the dark bottle, only R oxygen will decrease Light bottle Dark bottle
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Light-Dark Continued: Convert changes in oxygen to photosynthesis rate from “metabolic” equations Add oxygen consumed in the dark to get an estimate of gross (total) P Does not work well dark respiration and light respiration unequal bacterial growth can be artificially high when confined in a bottle
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2) 14 C tracer Incubate seawater in 14 CO 3 (bicarbonate) , and filter algae at a given time Measure radioactivity in algae with a scintillation counter Underestimates true rate because some photosynthetic product is respired quickly, converted to CO 2 and eliminated
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1 o varies geographically: estuaries > upwellings > coastal waters (without upwelling) > fronts > open ocean
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Estuaries Nutrient-rich, shallow systems rarely
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1-7 Pelagic Food Webs - Pelagic Food Webs Topic 9 Chapter 2...

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