Natural infections of aposymbiotic Cassiopea xamachana scyphistomae from environmental pools of Symbiodinium

The ability to acquire different types of the symbiotic dinoflagellate Symbiodinium (zooxanthellae) from the environment was investigated using aposymbiotic scyphistomae of the jellyfish Cassiopea xamachana. Non-symbiotic scyphistomae were placed on an offshore Florida patch reef and in Florida Bay during 3- and 5-day periods in March, and 5-day exposures in May, August and December of 2003. Scyphistomae were maintained in culture for several months, after which members of clades A, B, C and D Symbiodinium were detected in these hosts by denaturing gradient gel electrophoresis (DGGE) analyses. These findings contrast with naturally collected C. xamachana medusa from Florida Bay where all specimens possessed only Symbiodinium type A1. Furthermore, the polyps did not acquire the symbionts found in nearby cnidarian colonies, suggesting that a diverse pool of symbiont lineages exists in the environment. These results support previous laboratory studies where aposymbiotic hosts were initially non-selective and capable of acquiring many kinds of Symbiodinium. The specificity seen in adult hosts is likely a result of post-infection processes due to competitive exclusion or other mechanisms. A higher percentage of polyps became infected after 5 days of exposure, compared to 3 days, and no infections were observed in laboratory controls held in filtered seawater. Infections were lowest (50% at both sites) in March of 2003, when seawater temperatures were at their annual minima. Infection was 100% in scyphistomae exposed for 5 days during the months of May, August and December of 2003. These findings suggest that this host system, in addition to addressing questions of host-symbiont selectivity, can be employed to monitor and define the abundance and distribution of natural pools of Symbiodinium.