Daphnia Collecting Techniques and Discoveries Part III
by Howard Webb (St. Louis, MO, USA)

Part one of this series.
Part two of this series.
Part four of this series.

Plankton nets are not cheap to buy, and though there are numerous plans for making them, the sewing and construction can get complex (for a relatively easy, and good design see Howard Taylor's rotifer net). I decided to see what sort of net I could create cheaply and easily, and what results it would produce.

The Equipment Basics:
I had seen a butterfly net that looked like someone had taken some fabric and held it in place with a needle-point hoop. While a wooden needle-point hoop might not hold up very well in water, it was the start of an idea. I sliced a 1 inch ring off a 6" PVC pipe, and drilled several holes around the edge for attaching a tow line. Combined with a 6" hose clamp, I now had a hoop to hold the net. For the net, I borrowed (permanently - she no longer wants it back) one of my wife's knee-high nylon stockings. It may look a little funny, but it definitely does a nice job. The weave is fine enough to collect small daphnia and algae. I have not experimented to see if different styles of stockings produce different results.
I tried several attempts at throwing the net out from the shore of a pond and pulling it back in, but so far this has had poor results (possibly due to location as much as technique).

My first good results were when I bribed my sons into going with me on a daphnia collecting trip to Forest Park, by promising them a paddle-boat ride. They merrily paddled along while I towed the net about 12 feet behind the boat. It is a relatively shallow pond (more a reflecting pool left over from the 1904 Worlds Fair), but the results were astounding. The net had a 1/4 inch layer of algae coating it, and a rich population of daphnia. All the more interesting as they were new genera (to my collecting), being small pelagic species (Chydoridae and Bosminidae).

While on vacation in Michigan, we spent several days at the Lake Michigan beaches around St. Joseph. While the kids played in the sand, I was looking out to deeper water, wondering what it would take to get a boat and go out towing. Accepting the fact that I had to stay family oriented, I started wondering if there was anything along the shore worth collecting. Rather than towing the net, I tried holding it like a hoop seine (holding the fabric up so only a portion of it covered the opening) and waving it back and forth through the water. Every little bit I would rinse the fabric in a small container; in this way, I was able to concentrate the plankton into denser quantities. Lake Michigan is cold (I probably need to add a thermometer to my collecting equipment), so I didn't venture out beyond knee depth. From prior bottle collecting in the waves, I knew there were some interesting daphnia. Most of the animals were copepods, but again I found some new genera.

June 17, 2001 - Forest Park, St. Louis, MO (UTM 15 736122E 4280027N)

100x, 'best' quality image.
(Resized, click for original).

100x, 2x digital, 'good' quality image

July 25, 2001 - St. Joseph (Tiscornia Park Beach), Michigan (UTM 16 542244E 4662566N)

Tiscornia Park Beach
St. Joseph, Michigan

Tough assignment, but somebody has to collect here.



100x, 2x digital, 'good' image

Detail of Chydoridae
400x, 'best' image.
(Resized, click for original).

40x, 'best' image. (Resized, click for original).
These were the most abundant species in my collecting. Being predators, they quickly take over a collection jar, and eliminate most of the daphnia.

100x, 2x digital 'good' image

100x, 2x digital 'good' image

At the Maritime Museum in South Haven, I saw the above article about Bythotrephes cederstroemi (spiny water flea); a European species of daphnia that apparently was transplanted via ship bilge water to the Great Lakes. While the text of the article is correct, I believe the pictures are really D. galeata mendotae.

D. galeata mendotae
100x 'good' image

D. galeata mendotae
100x 'good' image

D. galeata mendotae
100x 'good' image

For little work, the net adds a lot of value to my collecting. It is small enough to fit in a back-pack, so is easy to carry around on the off chance it may be useful. It will definitely become another one of my standard tools, to be pulled out at opportune times.

Technical Note on Photographs:

All pictures were taken with my Kodak 3200 digital camera. The 'good' images are about 576x432, while the 'best' images are 1,152x864 (1 megapixel). The photomicrographs have been cropped, but not enhanced or resized (except where stated).

The Maritime Museum is accessible at: www.michiganmaritimemuseum.org

Comments to the author Howard Webb are welcomed.

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