Variation in Symbiodinium communities in juvenile Briareum asbestinum (Cnidaria: Octocorallia) over temporal and spatial scales

Despite the importance of cnidarian-algal symbioses for the reef ecosystem, little is known of the pattern of symbiont acquisition in juvenile octocorals and how this varies across time and environment. To study this, aposymbiotic larvae from the common Caribbean gorgonian Briareum asbestinum were placed in distinct habitats in the middle Florida Keys, and the establishment of the symbiosis was monitored yearly during 1999-2002. Although Symbiodinium B184 (type based on length variation in domain V of chloroplast large subunit [23S]-ribosomal gene) dominated juvenile B. asbestinum for up to 12 mo, other symbiont types within Clades A, B, C and D co-occurred with B184 at varying frequencies across years and sites. The occurrence of some symbiont types (B184 and B224) did not differ between habitats or years monitored, while other symbiont types (A194, B220 and C180) varied significantly in prevalence depending on year and site. The diversity of symbiont types initially acquired by young juveniles was not simply a subset of the symbiont types found in nearby host cnidarians, suggesting that the source of infecting symbionts was not solely local host populations. Experimental manipulations demonstrated that symbionts continued to enter the host for several months until a single symbiont type dominated within the juvenile octocorals after 3 mo. Although some symbiont types varied significantly across habitats, the pattern of infection did not reflect a given habitat. Instead, aside from Symbiodinium B184 and B224, initial symbiont acquisition appeared random in B. asbestinum recruits.