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Ostracode sample preparation, extraction and identification

By: J. Bunbury

Processing sediment for ostracodes is relatively simple. It should be noted that this is the method that was used for surface sediment samples that needed little disaggregation. I suspect that when doing core samples, disaggregation will be necessary using the Calgon method ( Holmes, J.A. 2002. In Smol, Birks & Last (eds) Tracking Environmental Change Using Lake Sediments, Vol. 4, pp.125-151, and references therein).

•  Start by subsampling between 5 and 10 cm 3 of sediment. Of course, it may be that much less sediment is required if working in temperate regions (my samples were from north of 60°, see below). To avoid breaking the shells, I used a modified 10 cm 3 syringe with an aperture of 1.5 mm that worked quite well.

•  Sieve the sediment carefully through 50 µm Nitex ® mesh under a gentle stream of tap water. Rinse the remaining sediment and ostracodes with deionized water and transfer to a petri dish.

•  Pick the valves with a 0/5 brush using a 16x stereoscope (method is modified after Danielopol et al. 2002 In Holmes & Chivas (eds) The Ostracoda: Applications in Quaternary Research, pp. 65-97). I found it necessary to pick the valves immediately after processing my sample to avoid damaging the shells with the less alkaline, more neutral tap water. Picked valves were mounted on micropaleontological slides with water soluble gum tragacanth (Delorme, L.D. 1967. Canadian Journal of Zoology. 45: 1275-1280). Once picked the remaining sample is stored in a 20 ml screw top vial.

It was not clear how many valves should be picked per sample for quantitative analysis. It depends largely on the region you are in (ostracodes per gram of sediment can range from <1 to >6,000), depending on location (Griffiths & Holmes 2000. Non-marine ostracods and Quaternary paleoenvironments. Technical Guide No. 8, London: Quaternary Research Association, pp. 188) . Also important is how much sediment is available and the type of results you want to obtain. I found a good way to justify the number of valves per sample was to prepare a species acquisition curve for each lake. The cumulative number of valves was plotted against the cumulative number of species. Counting stopped when the richness curve leveled off (modified from Henderson & Walker 1986, Journal of Tropical Ecology. 2:1-17). See Griffiths & Holmes 2000 for an example, or see my examples of species accumulation curves from Sulphur, Scout and Rat Lakes in the Yukon. As an example, in the southwest Yukon I picked between 4 and 35 cm 3 of sediment before my species acquisition curves leveled off. In some cases, my curve had leveled off, but I needed to finish picking my sample.

Identifications were done under 80x magnification using a stereomicroscope. Taxonomic references can be found in our library.



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