Zooxanthellae Density (ZD)

As aquarists, we go to great lengths to provide an environment that is suitable for the growth of our corals. In many respects, we are really providing a suitable environment for the symbiotic zooxanthellae (zoox.) within our corals. Most of us take Symbiodinium microadriaticum for granted but without it, our favorite reef building stony corals could not survive. Even though zoox. are critical to our favorite corals, only recently have advanced sps keepers and zeoheads started to speak of coral health and vitality in terms of zooxanthellae density (ZD). After a lot of tinkering with camera settings and setups, I am on the brink of discerning individual zoox. cells. With a lot more work and some custom imaging software, I hope to develop a non-intrusive method for quantifying ZD.

Assuming that all the visible brown spots are zooxanthellae, I counted a minimum of 82 cells. Placing your cursor over the image will highlight these. I omitted dark spots in the lower left corner of the image because I can't differentiate the spots from shadows but there certainly is some zoox. there. I approximate the scale of the image to be 0.5-1mm diagonally, or 0.25-1mm2 which gives a ZD of 8200-32,800 cells/cm2. This is a reasonable range of values since it is expected that ZD should be pretty low at this area of new tissue growth. I will soon round up some references for ZD values for comparison. In my calculations, I assumed that the surface area of the coral was the same area as the image, but it's not. The acro tip is round, conical to tubular in shape and porous whereas the image is flat and "smooth". It goes without saying that this is a very rough, untested estimate of ZD but in time, it is my hope that the coral community can establish a protocol for referencing ZD using this technique.

The image above was made using a c-mount camera and the mesoscope adapter that Barry from Ogles let me borrow. the camera uses Delta Pix imaging software and unfortunately, I haven't yet had a chance to calibrate the reference bar to get a more accurate visual estimate of surface area. Following the trend of colonization of the coral tissue it is clear that there is a repeating minimum size category for the brown spots that I believe to be individual zoox. cells. Once I determine the surface area with more accuracy, I am going to use a GIS program called ArcView 9.0 to analyze the relative covered surface area. By assuming the image surface area is the same as the pictured surface area (which it isnt) and assuming that the surface thickness of the colonizing zoox. is only 1 cell thick (I dont think it is) I can use ArcView to rectify the image to a geographic coordinate system. I can then use arcview to assign a raster value to the differently colored pixels that can interpret to determine the coverage area of the zoox.
If you're still with me, it's really a longshot idea with a strictly 2-D interpretation of dynamic 3-D details. I am also making alot of assumptions and using a program designed for mapping the world to analyze a "map" of a microscopic area. I will bounce the idea off of some more knowledgeable persons in the zooxanthellae and GIS fields and I will see what they say. I could be off my rocker but it's worth a shot.