AME 40:163-173 (2005)  -  doi:10.3354/ame040163

ABSTRACT: A total of 6 planktonic naked ciliates were isolated from the Oslofjord, Norway. Numerical and functional responses were investigated using bottle incubations at 11 to 14°C, with the prasinophyceae Nephroselmis pyriformis and cryptophyceae Hemiselmis sp. as food. Growth rates followed hyperbolic curves, which levelled off at about 15000 algal cells ml^–1 (152 µg C l^–1). Highest growth rate was recorded for the large heterotroph Strobilidium spiralis (μ_max = 1.38 ± 0.08 d^–1 (mean ± SE). A small mixotroph, Strombidium vestitum, displayed high growth rates (μ_max = 1.04 ± 0.05 d^–1), compared to the larger strombidiids Strombidium conicum, S. acutum and Strombidium sp. (μ_max = 0.55 to 0.80 d^–1). Food thresholds for positive net growth rates were estimated to be in the range of 600 to 3300 algal cells ml^–1, or 6 to 34 µg C l^–1. Specific ingestion rates increased at increasing food concentrations, and maximum measured rates were generally in the range of 2 to 4 d^–1. S. spiralis increased its clearance rate to a maximum of 18.3 ± 0.69 µl h^–1 as algal concentrations were enhanced from 900 to 2600 algal cells ml^–1. Gross growth efficiency ranged from 7 to 52% above threshold food levels, with a mean and median of 22 and 23%, respectively.

KEY WORDS: Ciliates · Growth rates · Feeding rates · Clearance rates · Threshold · Gross growth efficiency · GGE