Serendipitous goop

Ok. I've been told to stop dawdling and get on with it.

Remember the white stuff that showed up in my aquarium leavings? Maybe not. Here's what I wrote then, September 30th:

Last week I emptied the tank, washed the sand, and replaced everything. As usual, I kept out the dirty water I'd washed the sand with, and let it sit overnight, just in case any tiny snails were hidden in the gunk. Normally, the dirt settles, and the snails climb to the top, where I catch them and return them to the tank, then dump the goopy mess. 

But this time, there was a white network of fibers just on top of the settled gunk, below the inch or two of clear water. I stirred the water again, and let it sit. Two hours later, there was the net again. Three times I stirred it; every time, white lines made a road map along the top two hours later.

And here are a couple of photos:

The white stuff is all tiny, almost straight fibers, growing at both ends.

Growing and spreading across the bowl. This is a patch about 3 inches across, IIRC.

I asked for help. People made suggestions in the comments: marine slime molds, mineral precipitation, salts. Nothing worked out.

Then, reading the article about sea star wasting syndrome by Ron Shimek, I found photos, a description and a reason that matched what I had found. They're bacteria; Beggiatoa sp.

The Reef2Rainforest photo:

Bacterial mat, in the wild.

"The black surface and white bacterial mat is exactly what would be predicted after a major mortality event in the sediment. The black sediment is made in anaerobic environments by sulfide loving bacteria. It is the result of significant decomposition in the sediments proper- where animals died and are now decomposing and releasing a lot of nutrients from their rotting bodies. ..." (From the photo text.)

The white is a characteristic bacterial genus named Beggiatoa. It has several species that metabolize hydrogen sulfide and decomposing critters. (From the caption of another photo.)

The mat in my bowl was on the gunk that I'd collected from washing the sand and the filter in my aquarium. It would have decomposing critter food, mostly shrimp pellets, and rotting eelgrass and sea lettuce. I could smell the shrimp, faintly. I had poured off the clean water as the muck settled, so there was only an inch or two of water over the black stuff; a concentrated mess of rotting animals and plants. It would be more acidic than the clean water I replaced in the tank; Beggiatoa likes acidity.

Beggiatoa lives in freshwater and marine environments. It is present in all the world's oceans, from shallow intertidal waters to the bottom of the deeps. It would be found in the stuff I bring back from the beach, but not in a concentration sufficient to form this sort of mat until I isolated it. I have tried to see if I could recreate the conditions and grow another batch, but not so far.

And they're fascinating bacteria! They are one of the largest prokaryotes (bacteria and similar organisms); up to 200 microns in diameter. That's 2 millimetres, the length of a small carpet beetle. And each filament may grow up to 1 centimetre. No wonder I could see them with the naked eye!

The metabolism of prokaryotes is far more varied than that of eukaryotes (That's everybody else, including us. -Me), leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, studied in cryobiology or as hot as undersea hydrothermal vents and land-based hot springs. (From Wikipedia)

Most Beggiatoa don't need organic food, nor sunlight, to grow.

They are one of the few members of the chemosynthesizers, meaning that they can synthesize carbohydrates from carbon dioxide and water using energy from inorganic compounds. Beggiatoa are found in polluted marine environments, and can be seen by the naked eye as a white filamentous mat on top of the water as a sign of environmental deterioration. (From MicrobeWiki.)

Not all Beggiatoa are white; some are yellow or orange; the white comes from granules of sulfur stored in the filaments.

As I saw, the filaments move about, both spreading, gliding along, and moving vertically. (How they do this, I couldn't discover.) "They respond to oxygen, light, and presumably sulfides."

They prefer the interface between a solid sulfide-containing base and oxygenated water, and use elements from both. In some situations, the surface sediment is oxygenated during the day, due to the the activity of algae in the sunlight. Then when the sun goes down, the oxygen is depleted and the sediment becomes anoxic. Beggiatoa pick up sulfides in the anoxic zone at night, then combine their sulfur with oxygen from the water in the daylight. A short video on YouTube shows this process.

They grow where there is an abundance of rotting organic matter, where the decomposition processes have resulted in an acidic, anoxic, sulfide-rich environment. This means that they may be a marker for pollution, such as sewer outfalls, or die-offs. But they do not contribute to the pollution; rather they help to return the area to a condition usable by more "normal" life forms.

So, while they showed up where the sea stars are dying, they are not the cause. Scientists are still looking. (Maybe it's a virus.)

More info.
The Genera Beggiatoa and Thioploca
And the original article, again.