Growth and consumption rates of bacterivorous Antarctic naked marine amoebae

Abstract

This IS the first study to consider the growth and feeding rates of naked marine amoebae at temperatures below 5°C. Specific growth rates were calculated for 5 Antarctic isolates, Platyamoeba australis, A4ayorella sp., Metachaos sp., Vannella sp., and an unidentified vahlkampfiid amoeba. Growth rates ranged between 0.08 X 10-l and 2.9 X 10-' h" corresponding to generation times of 866.2 and 23.9 h, respectively. All isolates grew at temperatures down to -2OC and showed optimal growth at 2°C although one species grew best at 0°C. A direct counting method was used to estimate bacterial feeding rates of P australjs and the vahlkampfiid amoeba. Rates varled as a function of prey denslty but were largely independent of temperature. Overall, amoebae consumed between 0.5 and 66.4 bacteria amoeba-' h-', equivalent to 0.3 and 38.0 pg C cell-' h-' Growth efficiencies estimated for these 2 amoebae were low, typically < 2 % , suggesting that amoebae incur high energetic costs for life at low temperatures.

Effects of temperature on growth rate and gross growth efficiency of an Antarctic bacterivorous protist

“…In theory, a significant relationship between GGE and growth rates of protists would not be expected because, unlike large, multicellular organisms, protists do not have significant basal respiration (Fenchel, 1986). Published data indicate that GGE of protists may increase, decrease or remain unchanged with changes in temperature (Laybourn and Stewart, 1975;Rogerson, 1981;Rassoulzadegan, 1982;Verity, 1985;Caron et al, 1986;Choi and Peters, 1992;Mayes et al, 1997;Ishigaki and Sleigh, 2001). GGEs measured in this study yielded a relatively narrow range of values, which did not vary consistently with temperature.…”

“…Some studies have reported increases in GGE with decreasing temperature (Rassoulzadegan, 1982;Verity, 1985;Choi and Peters, 1992), whereas others have reported decreases with decreasing temperature or very low GGE at extreme low temperature (Laybourn and Stewart, 1975;Rogerson, 1981;Mayes et al, 1997). Still others have reported no effect of temperature on GGE (Caron et al, 1986;Ishigaki and Sleigh, 2001).…”

“…Choi and Peters (1992) reported high biovolume-based GGEs (60% and 71%) for an Arctic and a subarctic P. imperforata measured at -1.5 1C. In contrast, Mayes et al (1997) reported exceptionally low GGEs for Antarctic amoebae over the temperature range -2 to 4 1C (GGE ¼ 0.8-7.2%).…”

“…The authors interpreted these results as indicative of adaptation by the Arctic P. imperforata to low environmental temperature. Mayes et al (1997) reported growth rates for five species of Antarctic naked marine amoebae over the temperature range À2 to 4 1C. The observed growth rates of these amoebae were significantly less than the rates predicted for their growth at ambient Antarctic temperatures by the extrapolation of available growth rate information for temperate amoebae.…”

“…Thus, the extrapolation of physiological rate information obtained from temperate cultures to infer rate processes of protists in permanently cold environments may be inappropriate. To date, three published studies have examined growth rates of cultured heterotrophic protists from permanently cold environments (Lee and Fenchel, 1972;Choi and Peters, 1992;Mayes et al, 1997). All three studies reported low growth rates of polar isolates within the range of ambient polar temperatures (À1.8 to 2 1C).…”