Ciliophora
Provenance and collection of materials

For enumeration of aloricate ciliates only whole-water techniques are recommended (Gifford, 1985; Finlay and Guhl, 1992; Pierce and Turner, 1992). Usually, several hundred millilitres to some litres of seawater are collected by various types of water bottles (Venrick, 1978b). Whereas small capacity bottles are adequate for biomass-rich inshore waters, larger bottles are necessary for the oligotrophic open ocean. However, the latter usually lack mixing devices, so grave errors in abundance estimates may result from under-representation of particles settling rapidly in subsamples (Gardner, 1977). Containers provided with windows, like Van Dorn bottles, pose the problem that light-sensitive species may move to or away from them, which can bias subsampling. Standard Niskin bottles may be toxic to protozoa, therefore ultraclean techniques or GoFlo bottles should be used instead (Fitzwater et al., 1982; Chavez and Barber, 1987).

For elucidation of the vertical or horizontal micro-distribution, special water samplers take several samples simultaneously at 10-20 cm intervals (Blaker, 1979; Owen, 1981). They collect only rather small amounts of water, but if used in a chlorophyll-maximum or density discontinuity, the number of organisms may be adequate for meaningful data (Paranjape, 1991). Macro-aggregates and associated ciliates are best collected by scuba divers or submersibles (Silver et al., 1978; Caron et al., 1982).

Pump samplers have to be chosen according to mode of operation and study requirements (Beers, 1978; Miller and Judkins, 1981). They can be used either at discrete depths or for sampling over vertical, oblique, or horizontal paths. Additionally, they can be fitted with continuous-flow sensors for measuring physical and chemical parameters (Paranjape, 1991). Mechanisms also have been developed for keeping the pump-intake at constant depth even when the ship is rolling (Paranjape, 1991). While pumps are capable of collecting all size-classes of ciliates, cells may become damaged or lost during concentration and fixation (Sorokin, 1977, 1981; Dale and Burkill, 1982). Pumped samples thus underestimate the ciliate population. However, compared to bottles or nets, they may yield much better spatial resolution.

Plankton nets and screens are unsuitable for quantitative sampling because a large proportion of the individuals is lost (Gifford, 1985). In nets of 20 and 44 µm mesh size, for instance, losses of aloricate ciliates ranged from 74-98% (Brownlee and Jacobs, 1987). These simple tools may thus only be utilized for a qualitative taxonomic survey. For this, a mesh size of 10 µm or less is necessary to catch the many smaller aloricate species. As ciliates are often slender and very flexible, even 50 µm long specimens can pass through the pores of a 10 µm screen (Foissner et al., 1991). So nets have to be towed very gently. Sediment traps are equally unsuitable because they collect the ciliate population incompletely (Antia, 1991), and species may multiply or disappear in the containers.