The use of a dissection microscope with magnification of at least 40X is necessary for proper veliger detection. A cross-polarized light filter makes detection relatively easy.
Prior to beginning analysis for any sample that might contain zebra mussel veligers, proper zebra mussel containment protocols must be observed in all laboratories for all equipment. Refer to Protocol for Responsible Monitoring Procedures for further details.
Zebra and quagga mussel veligers are most frequently confused with Corbicula veligers and ostracods. The Identification section provides details on identifying zebra and quagga mussel veligers.
Qualitative Analysis of Veliger Samples:
Qualitative plankton samples provide presence/absence information. The main goal of sample analysis for these samples is to find and identify any veligers that may be present. Collection information for the sample (site, date, replicate #, collection depth, water temperature) should be recorded with the results of the analysis. For information on record-keeping, see Importance of Maintaining Long-Term Records of Monitoring Data.
Equipment: Dissecting microscope with magnification of ³40X, microscope slides, disposable Pasteur pipettes, rubber bulbs, dissecting tools, and polarizing filters.
Protocol: Sequentially examine aliquots of water samples under a dissecting microscope. In unpreserved samples, veligers may be visible swimming or resting on the bottom of the dish. Veligers nearing the settlement stage may even be moving around using their foot. If the purpose of the sample is to determine mortality rates, then it should be examined without delay. Otherwise it can be preserved in a solution of 70-percent ethanol or 5-percent formalin. Counting may be especially hard when veligers are swimming around in and out of the field of view.
Quantitative Analyses of Veliger Samples:
The main objective of any quantitative sampling protocol is to enumerate the zebra mussel veligers found within the area sampled. Unlike qualitative sampling protocols, quantitative protocols go beyond presence/absence data. It is very important that careful field notes and lab records be kept when collecting and analyzing quantitative samples. For further information on record-keeping, see the Importance of Maintaining Long-Term Records of Monitoring Datasection. The ability of any sampling method (quantitative or qualitative) to detect veligers is limited by the volume of water sampled, the number of subsamples examined, and the concentrated volume of the sample (Marsden 1992). In areas where veliger abundance is thought to be either nonexistent or very low, a low detection limit is desired. The detection limit of any technique is calculated using the following formula (Marsden 1992):
(1 veliger/total subsample volume [ml]) x (volume conc. sample [ml])
vol. water sampled [ml]
To lower the detection limit of a sampling program, the number of subsamples examined should be increased.
Analyzing Plankton Tows, Pumped Samples, and Shallow-Water Samples
Use of Cross-Polarized Light for Veliger Detection
Use of Sugar Solution for Veliger Detection
Calculating Veliger Densities from Sedgwick-Rafter Cell Counts
Obtaining a Subsample
Analyzing Filamentous Substrate Samplers for Veligers