Marine Food Webs - The Diigo Meta page

• 15 May 12
  

  Katy Baker

  Has good basic food web for Arctic marine ecosystems. Use the food web as a template for your own.

  Food Webs Marine Arctic ocean

• 22 Aug 11
  

  jane Hunt

  fishing sustainability

  • Over Fishing Changes Food Webs

     

    We saw earlier that Cod stocks on Canada's  East Coast have failed to rebound more than a decade after the fishery  was closed. Now, Kenneth  Frank and colleagues have reported the results  of their study of changes in the food web in the large eastern Scotian  Shelf offshore of Nova Scotia, Canada. They found that the removal of  cod and other large fish changed the entire structure of the food web  from top to bottom:

     
     
    1. The population of small fishes and large invertebrates, including  northern snow crab and northern shrimp increased markedly.
     
    2. The population of large plant-eating zooplankton (> 2 mm) decreased  markedly.
     
    3. Phytoplankton increased markedly.
     
    4. Seal populations are increasing exponentially.
     
    5. The economic value of the crab and shrimp fisheries now exceeds  the earlier value of the cod fishery.
     
    6. Actions to restore the cod fishery have failed despite a nearly complete  shutdown of cod fishing.
     
    7. Cod stocks in other areas north of 44 degrees North have also failed  to recover, while cod stocks in areas south of 44 degrees North have  started to recover.
     
     

     

    
      The cascading effect of the collapse of cod and other large predatory  fishes on the Scotian Shelf ecosystem during the late 1980s and early  1990s. The size of the spheres represents the relative abundance of  the corresponding trophic level. The arrows depict the inferred top-down  effects.
      From Scheffer (2005).

     

     

    The changes in marine ecosystems due to over fishing is often called fishing  down the marine food web. As top predators are removed by fishing,  fishers target smaller fish lower in the food web, reducing their numbers.  This reduces the average trophic level of the food web. Trophic levels  are based on the food eaten at that level. Level 1 includes phytoplankton,  level 2  includes zooplankton, level 3 includes bait fish, etc.

     

    
      Fishing down the marine food web. After the  large fish at the top of the food web are fished out, fisheries go after  smaller fish and invertebrates at lower levels in the food web while  their trawling destroys animals and plants on the sea floor. Time  increases toward the right along the blue arrow. Scale on the right gives  the trophic level in the food web.
      From Pauly (2003).
• 02 Jan 10
  

  Lisa Durff

  marine biome biomes habitats ecosystems

• 19 Jul 08
  

  Ryan Keser

  Science Resources

• 28 Apr 08
  

  Rebecca Johnson

  Shows Marine Food Webs -also talks about how fishing changes food webs

  ecology_unit FoodWebs bluefin

• 04 Oct 07
  

  globalhorizons globalhorizons

  gh708 oceans rbe

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