Plankton Harvest:  Recycling Waste Nutrients to Improve Yield and Sustainability

 

Keywords:  plankton, harvest, polyculture, pond, biomass

 

Presented as:  BIO-MECHANICAL PLANKTON HARVEST:  A CONCEPTUAL MODEL FOR THE CULTURE OF MULTIPLE SPECIES.  Aquaculture 2001 -- The international triennial conference and exposition of the World Aquaculture Society, the National Shellfisheries Association and the Fish Culture Section of the American Fisheries Society. Book of Abstracts, p. 704. (click here for Slide Show)

 

William A. Wurts

Kentucky State University CEP

www.ca.uky.edu/wkrec/Wurtspage.htm

Polyculture is practiced throughout the world.  Several species of aquatic animals are stocked simultaneously to take advantage of the different food niches available in the pond environment.  In many systems, the primary culture species is fed a prepared diet.  The resultant wastes stimulate large phytoplankton populations, which in turn support several species of zooplankton.  On a dry weight basis, plankton can account for almost half of the standing biomass in a culture pond (900-1000 kg/ha).  Phytoplankton and zooplankton represent the largest niches of surplus food available in commercial production ponds.  As such, filter feeding animals, or planktivores, are stocked as additional species in polyculture ponds.  This increases production efficiency overall and minimizes the loss of waste nutrients.

 

Each of the filter feeding species stocked is permitted to graze simultaneously on the same plankton populations.  Essentially, these animals feed parallel to one another.  Filter feeders screen planktonic plants and animals non-selectively from the water column on the basis of particle size.  These planktivores consume phytoplankton and/or zooplankton.  By filtering small particles, such as phytoplankton and minute zooplankton, herbivorous planktivores would remove larger plankton as well and would negatively impact the numbers of large-size zooplankton, decreasing zooplankton populations overall (total productivity and standing biomass).  The filtering activity of animals that rely primarily on phytoplankton for subsistence would reduce the harvest biomass of planktivores that depend solely on intermediate and large plankton (particles) for food.

 

To improve the efficiency of plankton harvest, filter feeders should be placed in a series arrangement, flowing plankton rich waters past animals that feed on the largest plankton first and to those that consume the smallest plankton last.  Each of the different planktivores should be compartmentalized according to the size of the particles they filter.  Pond water could be pumped, from one enclosure into the next, through a series of floating or land-based chambers.  Removing plankton sequentially, big particles first and small particles last, would improve net filtration efficiency and increase the (potential) biomass of planktivores at harvest.  Careful selection and segregation of filter feeders for an aquaculture system could, in theory, double the harvest biomass in a production pond without significant deterioration of water quality.  Waste nutrients would be recycled indirectly through the planktivores.

 

For related information click on the topics below:

 

MODIFIED POLYCULTURE

In:  Reviews in Fisheries Science, 8(2): 141-150

SUSTAINABLE AQUACULTURE IN THE TWENTY-FIRST CENTURY

Reviews in Fisheries Science, 8(2): 141-150

 

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