The Cladocera Interest Group

Identification

 

Methods for Collecting Cladocera

by Hannah Robson

      Below are several methods which are tried and tested for collecting Cladocera for further preservation and identification. We envisage adding further methods as time goes by and would welcome suggestions from other workers who have devised or used novel methods or equipment.

Kick sampling

      This standard method for sampling invertebrates in freshwaters involves disturbing sediment/vegetation with ones feet whilst either positioning the pond net downstream (in the case of running water environments) or by sweeping the net back and forth over the disturbed area (in the case of still water habitats). This method will frequently pick up some cladocera in addition to larger invertebrates however it is important to be aware that typical pond net mesh size (1mm) will not catch smaller cladocera species. Once emptied into a white sorting tray claodocera can most easily be collected sucking them up with a plastic pipette.

      Equipment needed: Pond net, white sorting tray, plastic pipettes/spoons, sample tubes/pots, alcohol to preserve

      Advantages: Can be done in conjunction with traditional invertebrate sampling, includes a range of habitats

      Disadvantages: Will miss small species if using a large mesh size net. Difficult to use in very shallow / silty pools.

Plankton net sampling

      These nets can be usefully employed to collect planktonic claodceran species at a range of depths in the water column. The net is thrown out into the water and dragged back towards the sampler fairly quickly so it remains at a similar height in the water column and is not dragging along the bottom. Pulling the net very quickly results in the net being half out of the water and so sampling any surface dwelling cladocera or indeed any under floating leaved vegetation.

      Alternatively the net can be dragged behind a boat. Specimens can be washed towards the bottom of the net and collected from the unscrewable sample jar / filter and washed into a pot with alcohol or other preservative.

      Another alternative method, best used from a boat, is to attach a weight to the closed or 'cod' end of the plankton net. The net is lowered vertically through the water body until it touches the bed of the pond / lake. Hauling the net vertically up then samples the water column catching species at all depths. A variation of this is to do a series of hauls from different depths in order to reveal any variation in species distribution with depth, which can obviously also be done at varying times of day to establish any daily movement of species and relate to temperature, light intensity or other variables.

      Equipment needed: Plankton net, sample pots (wide mouthed are easier),preservative

      Advantages: price considerably lower than traps / grabs, can be used in a range of habitats/water depths

      Disadvantages: Difficult to sample benthic species without clogging net

Sediment grabs

      Mechanical grabs can be used to collect a quantifiable amount of surface sediment, which can be examined for benthic Cladocera and fossilised remains. The exact method varies based on the design of the grab sampler, the sampler is set and lowered through the water column until it contacts the surface sediments at which point the grab is tripped (again how this occurs depends on the grabs design) and the jaws of the grab close collecting surface sediments within. Once the grab has been raised to the surface the sample can then be washed / cleaned through a pond net or collected intact for later subsampling.

      Equipment needed: Grab (more easily deployed from a boat), fine mesh pond net, small buckets / tubs for collection / transport, preservative

      Advantages: Quantitative (collects a known volume of sediment)

      Disadvantages: Cost of grab, not possible to use on hard substrates /rocks /boulders

Schindler-Patalas trap

      The Schindler-Patalas trap consists of a clear plastic box with a fine mesh net attached near the bottom (see image);

the trap is lowered through the water column to the desired depth and then sealed. Once raised to the surface the contents of the trap can be collected in the fine mesh net and emptied into sampling container.

      Equipment needed: Trap, more easily deployed from a boat

      Advantages: Quantitative (can sample a known volume of water from a known depth)

      Disadvantages: Price of trap, or difficulty in making.

Myvatn type cladocera trap

      The Myvatn trap is adapted from the Whiteside & Williams (1975) plankton trap (see image).

The trap is lowered into place and positioned approximately 3-5cm above the sediment surface, it is left in place for a pre-determined number of hours before being collected, for more information on deployment see Björk Örnólfsdóttir & Einarsson (2004) from which the illustration above is copied the full paper is downloadable from: https://www.researchgate.net/publication/225224642_Spatial_and_temporal_variation_of_benthic_Cladocera_Crustacea_studied_with_activity_traps_in_Lake_Myvatn_Iceland It should be noted that in this trap the only cladocera caught are those which actively swim into the trap since the jars are pre-filled with clean filtered lake water before lowering the trap.

      Equipment needed: Trap, boat to deploy.

      Advantages: Set sampling area, easy to deploy /collect

      Disadvantages: Need to make / buy the trap