LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA, CNIDARIA)

Symbiodinium californium (#383, >Banaszak et al. 1993) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5 degrees C-30 degrees C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15 degrees C and 28 degrees C (mu 0.21-0.26 center dot d(-1)) and extremely low at 5, 10, and 30 degrees C (0.02-0.03 center dot d(-1)). Average doubling times ranged from 2.7 d (20 degrees C) to 33 d (5, 10, and 30 degrees C). Cells cultured at 10 degrees C had the greatest cell volume (821 mu m(3)) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light-saturated maximum photosynthesis (P-max) increased from 2.9 pg C center dot cell(-1) center dot h(-1) at 20 degrees C to 13.2 pg C center dot cell(-1) center dot h(-1) at 30 degrees C, a 4.5-fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30 degrees C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.