Determine the area of the river water area that is required to feed a 1 kg pike perch (30% dry matter) in the food chain

Determine the area of the river water area that is required to feed a 1 kg pike perch (30% dry matter) in the food chain: phytoplankton – herbivorous fish – zander. Productivity for phytoplanton 700g / m2

Answer: 42.9 m2.
To begin with, we find the dry weight of pike perch, 30% of the total mass of 1 kilogram is 300 grams. According to the rule of the ecological pyramid, in order to grow a 300-gram pike perch, 3,000 grams of herbivorous fish and 30,000 grams of phytoplankton are needed. Since the productivity of phytoplankton is 700 g / m2, you can find out how much it is for zander: 30,000 / 700 = 42.9 m2.