Copepoda
Methods

Copepods inhabit different environments and, depending on what kind of copepods are collected and the final purpose of the study, different gear is utilized. For the purposes of quantitative and/or qualitative study of the pelagic copepod fauna, standard plankton nets are used. There are a variety of such nets (Juday's, Nansen's, 0.5 mö2, 1 mö2 cone nets, Bongo nets, plankton traps, etc.). The nets may have closing systems so they sample at known depths (for stratified sampling), or be without such systems for integrated hauls to the sea surface. As well as this standard equipment, special gear is employed for example for ecological studies of benthopelagic copepods as sampled from the D.S.R.V. "Alvin", or the study of the distribution of sound scatterers (Wishner, 1980; Gowing and Wishner, 1986, etc.). When copepods are not collected for in vivo experiments and live observation, but for the later study of preserved material (taxonomy, distribution, gut-content analysis, etc.), they are usually preserved with 2.5-5% formaldehyde, glutaraldehyde or 70-75% ethanol (the latter not commonly used as it makes copepods fragile), as well as other less commonly used preservatives.

The identification of copepods is often impossible without the previous dissection of specimens. Dissection is performed with fine dissecting needles and forceps. Dissected limbs are placed on a slide and are examined in lactic acid, glycerin (usually mixed with distilled water), or are mounted permanently in euparal, polyvinyl lactophenol, Berlese's Fluid, Canada Balsam or some other mounting medium. There are a variety of mounting techniques with corresponding preferences according to the respective purpose (for instance for the observation of integumental organs: Koomen and Von Vaupel Klein, 1995). Prior to dissection, clearing and staining of the specimen is recommended to make small morphological structures more easily observed under the light microscope. A brief but extensive review of the methods for fixation and preservation, mounting and sealing media, slide preparation, and scanning electron microscopy may be found in Huys and Boxshall (1991, pages 446-454). The illustrative material accompanying copepod studies varies. Usually line drawings, made using a camera lucida or other drawing apparatus, are used. Scanning electron micrographs also illustrate some taxonomic descriptions and cinematographic observations of feeding and reproductive behaviour are recent additions to available techniques.