OCTOPUS SPRING - 2 - Cool Water As water flows away from the pool and cools down, the microbial mat communities change. The pink colonies of bacteria give way at ~60°C to more familiar green of mats dominated by cyanobacteria (blue-green algae). At lower temperatures, eukaryotic algae (green, brown, etc.) come to dominate. |
|
||
Below the pool ~ 5 meters, reddish and greenish microbial mats grow in slow-moving, cooler water outside the main channel. Here, T ~60°C, pH = 8. The mats include a cyanobacterium (Synechococcus) that does oxygenic photosynthesis, and a green non-sulfur bacterium (Chloroflexus) that does anoxygenic photosynthesis. |
|
Ten to fifteen meters farther down the flow, water temperature is barely above air temperature and pH remains slightly alkaline. The microbial mats are probably filamentous cyanobacteria ("blue-green algae"), mostly Phormidium and Calothrix. |
|
|
|
|
||
In still water ~20 meters downstream from the spring, blue-green algae (cyanobacteria) forms cylinders and mushroom shapes instead of flat mats. These algal blobs resemble stromatolites, fossilized algal mounds that are found in rocks as old as early Archaean (>3 billion years old). [See "Stromatolites" for a closeup image.] |
|
The microbial mats are commonly layered, with different communities at different depths. The vertical layering usually comes about because different microbes have different requirements for light and chemistry. For instance, a lower microbial community might be shielded from intense sunlight by the upper community. Here, a brown community lies on top of a green community. |