Very often the amount of nutrients or of e.g. light changes rapidly over a very small distance. Here are some organisms that live in a gradient of sulfide and air, or at the surface of water. You are welcome to download the images. Annotations are included. If you want to see them first, click on ann .
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Here, long filaments at the edge of such a mat can be seen. Single filaments of Beggiatoa spec . At theirs ends the filaments sometimes divide into smaller, coccoid cells. The colony developed in the lab on a sulfide rich marine sediment from the Eel Pond, Woods Hole, MA, USA Phase contrast micrograph. 20 m ann Single filaments of Beggiatoa spec .