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.

The rotten egg zone

Boundary Bay is about 13 kilometres (8 miles) across at the base, and encompasses about 100 square kilometres. In the centre, there is deep water, but most of the northern end is a flat intertidal plain, filled with silt from two rivers and many creeks.

2009 Google map. The intertidal zone is shaped somewhat like an amphipod, looking towards the east.

The head and the spine of the amphipod are mud. Deep, maybe waist-deep, sticky, squelchy mud, continually replenished with run-off from the farms and bogs of the Delta brought in by the Serpentine and Nicomekl Rivers at the "head" end. It's bird and worm country; people can't walk there, don't even take their boats and paddle boards in that direction.

As the silt merges with the sand along the western shore, the mud develops a variety of disagreeable odours. Sometimes there are dead zones, where clams and crabs lie dead on the surface; the air smells of rotting flesh, choking and impregnating our clothes. At other times, everything smells fishy or of untamed compost heaps. These are often the result of human pollution; fertilizer and industrial contaminants, construction debris, oils and paints.

The more common rotten egg smell of hydrogen sulfide is almost pleasant in comparison. It is a sign of abundant organic matter, teeming with busy, happy life.

It all depends on the size of the mud particles. Where the sand is coarse, water flows through, carrying oxygen to the tiny critters living there. Mud worms in their burrows dance a slow, sinuous dance, pushing the water along; clams squirt water and sediment as they move about. We see it as clean sand. It's soft underfoot, but not sticky; we dig in it, walk on it, sunbathe on it. If we notice any odour, it is the fresh tang of salt water.

Where fine silt clogs the water passageways, the water becomes stagnant, and free oxygen is depleted. Life goes on, even in these conditions; after all, there's plenty of food. It just has to be metabolised differently. Some of the animals living here use hydrogen sulfide as an energy source. The sand, to us, looks mucky and off-colour. And smells of rotten eggs. We look for better places to play.

Sticky sand/mud. Lugworm heaven. 2008

Slightly wetter muck, with worm poop.

Where the oxygen levels are lowest (anaerobic or anoxic zones), the muddy sand forms a black layer, sometimes just below the surface of the tide flat, or in other spots some 6 inches down, depending on the ratio of sand to silt.

Further south along the shore of the Bay, although the silt doesn't reach quite this far, and we have acres of clean sand, there are still pockets of black sand underneath. Around the worm "mountains", there is often a circle of black sand that the worm has eaten and ejected to the surface.

If we grab a handful out of the black layer, it feels firmer than the sand around it, and, again, it smells of rotten eggs.

And this brings me to the mysterious network stuff I was wondering about a couple of months ago. Continued tomorrow.

No end to mysteries

I do routine maintenance on the aquarium, daily, and half the time, it seems that I have to say, "What on earth is that?"

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.

Monday evening

I looked at the clumps under the microscope: all I could see were tiny, straight threads. Watching one for a while, I could see it grow, lengthening at both ends. When I stirred the mix, I could still see shreds of threads, unconnected. But two hours later, there was the network again.

Monday evening, overview. The bowl is 6 inches across. This is about a 3 inch section.

I was gone for a day, and came back Wednesday afternoon. Part of the bowl was covered with a papery coat; the rest was still clumps of threads, some still making a road map.

Wednesday afternoon

Zooming in, Wednesday afternoon.

The filled-in areas looked like papier-mache pulp; all short, white fibers, arranged every which way.

Thursday afternoon. The "roads" are gone, replaced by individual clumps.

I looked at several of these clean clumps under the microscope. There was nothing to see but the white fibers, still short and straight, sticking out in all directions.

Zooming in. Nothing but white fibers on the dark background.

Over the weekend, the threads covered the whole area, without any organization into clumps or roads. When I shook the bowl Sunday night and again this morning, they disappeared, and returned in a couple of hours to the final, uniform covering. No roads, no clumps.

I don't even know where to start to find out what this was.