When examining freshwater samples in order to study microscopic algae called Desmids I normally kill and preserve whatever I have collected for two reasons. The first is that I can examine the samples at my leisure, usually weeks to months to years after collection and the second reason is that I can make accurate drawings of the algae that I find.

You might think that algae do not move. Don't believe it! They can and do move and anyone who has attempted to draw living algae can attest to this fact. There is another reason for killing the sample and I found it out by accident. One day when I had collected a freshwater sample I had forgotten to preserve the contents and it wasn't until some weeks later that I remembered to look at it. What I found were many dead desmids minus their contents and quite a few amoebae and rotifers which contained some desmids internally.

The photograph shown right is of such a rotifer which contains five such desmids (one Closterium sp. and four Tetmemorus sp.). So it now means that I need to preserve samples so that they will not be eaten. However, this can lead to other research to see what animals prey on. Brook, A.J. & W. Ells (1987) described amoebae feeding on desmids and Ells, W. (1990) wrote a note on invertebrates feeding on algae which included examining crustacean fecal pellets as well as observations of Oligochaete worms feeding on desmids and diatoms. H. Canter-Lund and J.W.G. Lund in their recent book (1995) have a chapter on Animals Feeding on algae complemented with some beautiful colour photomicrographs.

Mike Dingley
 

References.
 

Brook, A.J., & W. Ells. 1987. The Feeding of amoebae on Desmids. Microscopy V.35, part 7, pp.537-540.

Ells. W. 1990. Invertebrates feeding on algae. Microscopy. V.36, part 5, p.430.

Lund, H.C., & J.W.G. Lund. Freshwater Algae. Their microscopic world explored. Biopress Ltd. 1995. 360 pp. ISBN 0-948737-25-5.