Vilbig's Zooplankton

By Al Kohutek 

This document is a summary of the many e-mail conversations that I had with Bill Cody and the Pond Boss message board.  Bill by profession is an Algal & Invertebrate Taxonomist.  What is a Algal & Invertebrate Taxonomist?  Algal is any group of lower plants having chlorophyll but no vascular system and including seaweed and related freshwater plants.  Invertebrate is lacking a backbone and  Taxonomist is classification of animal or plants according to their natural relationships.  Bill has offered to help us identify our zooplankton (genus species).  If you are wondering what is genus species?  Genus is a category of biological classification that ranks between the family and the species and contain related species.  Species is a category of biological classification ranking just below the genus or subgenus and comprising closely related organisms potentially able to breed with one another. 

Bill has worked locally for the Univ. Of North Texas at Denton for zooplankton and algae identification and he is currently working with some samples from Lake Texoma for UNT.  For most, it takes quite a bit of training to become proficient at identifying zooplankton which is why there is not a lot of people that do it. Often the bug has to be individually removed and mounted on a slide for proper and positive identification. Sometimes the bug has to be taken apart (dissected) and the individual parts examined for positive identification.  Depending on which bug he has, he works from about 6 or 8 specialized books for zooplankton identification. 

I collected several samples of our zooplankton on March 30, 2003 and mailed them to Bill.   They were preserved with povidone-iodine (a name brand is Batadine).  The povidone-iodine needs to be 7.5% or greater of the total content of the product.  I used Walgreen's brand and it had 10% povidone-iodine.  Use about 2 Tablespoons per quart.  In an emergency zooplankton can be preserved in isopropal alcohol (rubbing alcohol), vodka or gin.  Bill prefers iodine based pickling agents because Iodine is a gentler and better fixative for these things. 

A common name for the bugs in the samples that I sent are called daphnia.  A lot of the daphnia had a black spot on their backs.  This spot is called an ephippium (plural ephippia). Ephippia form when the population is stressed and is about to crash. (when using the word crash, it means the population dies due to running out of food).  The ephippia are resting eggs, that are released when the bugs die and rest until the next time the conditions become favorable and they 'hatch' and produce a new group of bugs; probably next year or beyond. Hatching of ephippia caused the beginnings of your current zooplankton bloom.  There are normally 2 eggs in the ephippium.

From talking with Bill, he said……"These 'bugs' were definitely responsible for clearing the water. They filter & eat tiny things out of the water that are bacteria size and larger which during heavy filtration has a very big impact on water clarity".       So this would mean that when the bugs crash the lake goes back to normal with regards to water clarity.

Sample results

1) Dominant species was Daphnia pulex.  Bill Said.…"Features of this one do not have a real good match to Daphnia pulex but it is closer to Daphnia pulex than any other taxon.  Daphnia pulex can at times be somewhat variable and I think your bug at the time of collection belongs here. A collection at another time of year would verify this."

Other species present in the sample:
2. Skistodiaptomus mississippiensis - this is a Calanoida (calanoid) Crustacea
3. Diacyclops bicuspidatus thomasi - this is a Cyclopoida (cyclopoid) Crustacea ß not a filter feeder
4. Bosmina longirostris - this is a Cladocera (cladoceran)
5. Brachionus variabilis - this is a Rotifera (rotifer)

Bill said "All the above except Diacyclops bicuspidatus thomasi are filter feeders. They "cleared up" the water. Diacyclops bicuspidatus thomasi has seizing and biting mouth parts and is often predatory on unicellular plants, animals, small metazoans and other tiny crustacea."

"There are undoubtedly numerous more zooplankton species present in your lake. However these are the ones that were most abundant in the night surface sample during the bloom in late March early April 2003. The larger sample (taken from Al Kohutek's dock) had more numbers of Bosmina & Diacyclops in it than the sample in the bottle (taken from Jon Griffin's dock)".

For more information on Daphnia click here


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