World Builders™
World Builders™
Session Five  --  Seaweeds
Session Five  --  Seaweeds



   The Photic Zone: Light in the Water
   The Photic Zone: Light in the Water

The part of the ocean that is penetrated by light is called the photic zone.


     The tiny algae and bacteria that live in the ocean form the base of the food chain there. The primary producers in a food chain are always autotrophs, organisms that can manufacture their own food, often simple sugars, from the energy and materials in their environments.   In order to do this, almost all the autotrophs in the ocean need to have access to light.

     When  sunlight enters the water, it is absorbed and reflected back by particles in the water.  The deeper the water gets, the less light penetrates it.  Even under ideal conditions, the light barely reaches down 200 meters (about 600 feet) and very, very little of it gets that far down.

     When the water is muddy or has lots of tiny photosynthesizers in  it, sometimes the light gets down only a few feet.

     Seaweeds need light.  They use chlorophyll to manufacture their food, and some auxiliary (helper) pigments to soak up light and give it to the chlorophyll when the water is deep and light is scarce.  Check the page on colors of seaweed to learn more about this.


Seaweed Information Menu

Ocean Menu

Top of Page 


Header
from NOAA Photo Gallery
© 1996,1997, 1998, 1999, 2000, 2002, 2003.   Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at eviau@earthlink.net .