Sub-sampling of macroinvertebrates

EQUIPMENT 

  1. Sub-sampling tray (see Caton 1991) or another type of tray with a gridded pattern. 
  2. Tripod with sorting tray platform for field sorting (optional)
  3. Various size seives for removing materials from the sample in the field and lab
  4. Random number table or other random number generator
  5. Cookie cutter or other small square, about 6 x 6 cm
  6. Denatured ethanol
  7. Vials, approximately 20 mL or 3-5 dram; these are available in durable plastic or glass
  8. 1 – ½ gallon HPDE containers (field)
  9. Labeling tape and alcohol-resistant marking pens
  10. Forceps
  11. Tally counter (optional)
  12. Dissecting microscope (10x – 60x zoom) and a light source
  13. Data recording sheet (Example)
  14. Family level taxonomic keys (CLICK-HERE for an example)
PROCEDURE
To sort the sample, place the composited sample into the mesh bottomed sorting tray, similar to equipment described in EPA's 
RBP Maunal and by Caton (1991).  The tray is a 250-micron mesh bottom that is evenly divided into numbered sections.

Place the mesh bottomed tray into the plastic outer tray and add approximately 3 cm of water to facilitate the even distribution of debris. In the field, place the tray on a level tripod platform.  Evenly distribute the material in the tray and lift the mesh bottom tray out of the water.

Use the random number table to select a minimum of one-quarter of the sections. Use a cookie cutter or other similar device to segregate, and remove the macroinvertebrates from the selected squares with a small spatula.

Distribute the contents of the four squares into a separate white plastic tray with a small quantity of clean water. All the macroinvertebrates are removed with forceps and placed in a labeled vial of alcohol. An inside paper and pencil label is recommended as well as an exterior label.

A minimum of 300 specimens or ¼ of the tray is sorted. If necessary, randomly select additional squares to attain the 300 organism minimum sample size. All organisms are completely removed from all sub-sampled squares to avoid biasing the macroinvertebrate sample toward the larger, more visible species. A tally counter is recommended. Keep track of the number of squares sub-sampled in order to estimate the original macroinvertebrate density in the stream.  Identify the macroinvertebrates to the taxonomic level desired.

 CLICK-HERE to download the information above (Includes data sheet and labels)

 
REFERENCES 
 
1.  Chapter 7 - Living Waters: Using Benthic Macroinvertebrates to Assess Your River's Health 
2.  Chapter 7 - US EPA's Benthic Macroinvertebrate Protocols

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