in tropical seas, but just a few meters deep or less in rivers and swamps. Photosynthetic algae, called phytoplankton, live in the photic zone. Zooplankton—tiny free-floating animals—eat phytoplankton. This is the first step in many aquatic food webs. Below the photic zone is the dark aphotic zone, where photosynthesis cannot occur. Many aquatic organisms live on, or in, rocks and sediments on the bottoms of lakes, streams, and oceans. These organisms are called the benthos, and their habitat…
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