2008-06-01
Rotifers in my Rain Gauge
I noticed a little brackish looking water in the rain gauge on my balcony, always the geek I took a sample in to the microscope. It is amazing what life a little water open to the elements will collect.
In the murky broth was a reddish-brown biofilm which I initially assumed was a petal from nearby flower that had been blown into the water and was being digested by the organisms. Under the microscope it was revealed as a huge raft of filamentary algae and hundreds of thousands of bright red Haematococcus spores.
Attached to this jumbled raft were Rotifers happily churning the water looking for food. I've never seen live Rotifers before; they are amazing little machines. My cheap microscope only offers bright-field, but I could easily see their internal structure, their two red eye spots, striated muscles, and their jaws chomping away at their prey. The ciliated corona really stirs up the water, you can see Haematococcus circling in the strong currents produced.
At higher magnification the active Haematococcus could be visualised in detail. Most had distinct red Astaxanthin plastids in their cytoplasm along with their green chloroplasts and other structures. The two flagella could only just be seen to the point where they exit the theca.
I wasn't sure they where Hematococcus, but the colour seemed right. I let a drop of water dry out, fixed and stained the slide with Jenner's which let me visualise the full length of the flagella. I'm no microbiologist, but that gave me more confidence I was in fact looking at Hematococcus. The fixing process destroyed their theca and its delicate support structures, but combined with the living morphology it gave me reasonable confidence it was indeed a Volvocales of some description.
A few of the Haematococcus were seen in groups of 3-5 individuals inside the same theca. I am unsure if this is part of the reproductive cycle, the grouped individuals appeared smaller than other free-swimming ones. Maybe it has to do with their encystment process? Most in the sample where in cyst form, suggesting they weren't in very good conditions, maybe high salinity as the liquid in the rain gauge had been drying up and concentrating over time (and I live right near the ocean in the salty spray). I was able to fix and stain some of these groupings, showing the individuals had flagella which suggests multiple fissions instead of some kind of cystic process, the spherical cysts seem to rupture with added water and release non-motile cells that have to generate flagella before they can swim.
Also in the sample were Peranema (or some other kind of Flagellate that swims towards its flagellum). They didn't fix well and appeared to lose their flagellum or lyse completely. I was using Methanol as a fixant.
The Rotifers encysted before fixing, even if done very quickly by flooding the slide with Methanol. Methylene Blue stains their outer shell-like layer but seems to be acutely toxic to them, quickly killing them. I simply placed a drop of 0.3% solution in water on the edge of the coverslip and let it diffuse under. The Peranema were quite happy to swim around in obviously blue water but seemed to slow down quite a lot and take on some of the stain, killing them eventually. The cystic forms of the Haematococcus stained quite oddly with Methylene blue.
The photos and video were taken using my Canon IXUS 800IS held straight up against the eyepiece. This is a very non-optimal way of making micrographs, I'll have to invest in an digital eyepiece camera... To get good contrast I had to close the condenser so much the CCD noise is very apparent, precise focusing is also next to impossible with the small LCD display in the camera so the subjects are blurry too.
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