Micro-community Addendum to the Drawbridge Report by Cris


Among the sequence of aerial photographs in the Drawbridge Report by Cris is a very large brilliantly-green pond. While Cris was getting his kite aloft…

Small Kite_Launch Large_Green-Pond

I was sampling this large green pond on the right [north] of the levee. It turned out to have a moderately-high salt content, with 119-ppt [parts per thousand] saline, and a water temperature of 30.3-degC. Cris estimated 8% to 15% salt, based on the green color, which translates to 80-ppt to 150-ppt. Pretty good for salt estimation based on color.

What was startling, however, was that I only found round [coccoid] bacteria in the water.

Coccoid Bact 800X

Here you see three of these bacteria in a photomicrograph taken at 800X magnification, then enlarged even further by cropping out the image of the three bacteria.

Identifying species by such a photomicrograph is risky, at best, and the qualify of this picture is not helpful. I suspect they are some species of Halococcus, by the size [about 0.5-micron] and shape, as well as the salt concentration.

As the photomicrograph shows, however, Halococcus has some red pigment. So, why was the pond such a brilliant green? I think this is a light-scattering phenomenon, where the color green is determined by the wavelength strongly scattered, rather than the weak pigment in the tiny particle [bacterium] doing the scattering. This is, however, speculative.

In the aerial-photograph sequence Cris shows, you also see a large dull-green to weakly-red pond to the left [west] of the bright green pond. That pond was only about 81-ppt saline, with a temperature of 27.6-degC. The dominant species in that pond was a small, very spindly marine diatom that is probably a species of Cylindrothecia. The photomicrograph shown below was shot at 800X magnification.

Spindly diatom large red pond.

And the videomicrograph below this was also shot at 800X magnification. Click on the triangle in the center of the image to start the video.

Finally, I sampled one of the small bright-red ponds in the “ditch” between the two levees [the levee with the railroad on the south and the levee I was walking on the north]. These ponds were brilliantly-red in color. You can see its color here…


The bright red color suggests a high salt concentration, and, indeed, I measured 195-ppt saline. This color was probably the result of both a red Halobacterium species and red and green dinoflagillates, probably of the genus Gonyaulax.

If you look closely, you can see the two flagella frantically waving. This specimen is only weakly red, so it actually looks green. The red pigment varied considerably in different samples from this pond, some appearing green and others a brilliant scarlet. I picked this videomicrograph because it showed the flagella best. Look even more closely and you may see bacteria, probably species of Halobacterium, darting past.

The fate of these small ponds between the two levees is uncertain. Cris tells me that old maps identify what I called the “ditch” as a long salt pond. Earlier in the year the entire “long pond” was filled with water. Now, most of the narrow ponds that remain have gone dry and this one is rapidly evaporating. There are gates in the north levee that communicate with this narrow “ditch”, but opening those gates may not be part of the program to restore the area to salt marsh.

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