Symbiodinium spp. were isolated from Porites porites (JR02F2 and RD03) , Montipora capitata (JR12A7), Madracis mirabolis (RD02), Montastrea faveolata (RD04), Pocillopora damicornis (JR13E1), and an unknown coral (RD01). Growth rates and the distribution between motile gymnodinoid cells and sessile coccoid cells were determined in 200 µL cultures in 96 well dilution plates. Clones of each isolate were maintained in L1 medium (prepared with 34 ppt sterile Gulf of Mexico water), at 26oC with illumination provided at 100 to 150 mE m-2 sec-1 PAR (400-700 nm) during a 10:14 (light/dark) photoperiod. Under these conditions, generation times of nearly once per 24 hrs were observed for clones, JR02F2, RD01 and RD02, in log growth. Clone RD04 had a generation time of approximately 5 days. The fastest growing clones produced the highest percentage of motile cells (> 90) during the daylight portion of the diurnal cycle. Growth characteristics of selected clones were examined over a range of salinities, temperatures and PAR intensities. Salinities ranging from 25 ppt to 45 ppt had little if any affect on growth rate. At salinities less than 25 ppt significant decreases in growth were generally observed; no growth was common at 5 and 10 ppt. In most cases inhibitory effects of temperature were observed at temperatures greater than 29oC. For example, generation times for JR02F2 were slightly greater at 29oC than 24oC, but maximal growth rates were reduced approximately 50 to 90 percent at temperatures of 32oC and 34oC, respectively. The most sensitive clone, RD04, stopped dividing after two divisions at 29oC. The growth rate of JR02F2 and RD01 reached a maximum at PAR levels greater than 100 mE m-2 sec-1 and remained within a range of 0.75 to 0.85 divisions per day up to 390 mE m-2 sec-1.

Key words: climate change, coral, Symbiodinium spp., temperature