Ciliophora
Vertical profiles

The majority of ciliates is usually found in the upper 40 m in highly productive areas and between 50-75 m in low productivity zones, and decreases with depth (Fig. Ci 3a, Fig. Ci 3b ; Beers and Stewart, 1969; Margalef, 1973; Revelante and Gilmartin, 1983, 1990; Mamaeva, 1984b, 1986, 1990; Paranjape et al., 1985; Edwards and Burkill, 1995; Froneman and Perissinotto, 1996a). There may be one or sometimes two discrete abundance maxima. The first occurs at or near the surface (0-25 m) and the second at the thermocline if it is marked (Beers and Stewart, 1969; Margalef, 1973; Mamaeva, 1986, 1990; Sime-Ngando et al., 1992).

The vertical distribution of ciliate abundance and/or biomass frequently reflects that of the phytoplankton, and less distinctly that of bacterial biomass, indicating a predator/prey relationship (Fig. Ci 4a , Fig. Ci 4b , Fig. Ci 4c ; Beers et al., 1980; Strom et al., 1993; Dolan and Marrasé, 1995; Leakey et al., 1996). Mixotrophic species and the phototrophic Myrionecta rubra occur predominantly in the upper layer but are capable of diurnal vertical migrations (Dale, 1987; Stoecker et al., 1989b; Dolan and Marrasé, 1995). The latter species, for instance, usually occurs at the surface layer during most of the day and migrates down to 30-40 m at night (Crawford, 1989). Dolan and Marrasè (1995) even found a Myrionecta rubra peak at 80 m depth. At the surface and during red-tide blooms, when it reaches up to 254 x 10ö6 ind. per liter, Myrionecta rubra may be the numerically dominant species (Fenchel, 1968; Leppänen and Bruun, 1986). Too few data are available to define depth zonations for other species.