Dataset: 16S rRNA sequences for outplanted Acropora cervicornis sexual recruits

A pervasive association exists between the bacterium Aquarickettsia rohweri and Caribbean Acropora, as A. rohweri dominates microbiomes of field-collected samples of this coral species. In particular, this bacterial species is highly abundant in genotypes of A. cervicornis susceptible to white band disease with reduced abundance in disease-resistant genotypes. A. rohweri, a member of the order Rickettsiales, is hypothesized to be an obligate symbiont dependent on the coral holobiont for nutrition and energy. Many other closely-related parasites within Rickettsiales are transmitted vertically, and A. rohweri is unlikely to persist in a free-living stage due to its limited metabolic capabilities. This bacterial parasite was therefore expected to be transmitted vertically between host generations. However, phylogenomic analyses of Acropora spp. and A. rohweri did not reveal the co-evolutionary characteristics expected of a vertically transmitted symbiont. These characteristics could be obscured, however, by horizontal transmission between hosts. The identification of A. rohweri in evolutionarily distant aquatic hosts ranging from ctenophores to sponges also strongly supports horizontal transmission of this species. To better understand the transmission dynamics of Aquarickettsia, populations of this bacteria were quantified in early life stages of A. cervicornis (gametes, planula larvae, early sexual recruits, and year-old juveniles) produced and raised in the land-based nursery at Mote Marine Laboratory in the Florida Keys. These corals were produced via controlled two-parent crosses involving six different genotypes across three annual spawning events. We found that Aquarickettsia was absent from captive-raised individuals though present in parental genotypes maintained in Mote Marine Laboratory’s in situ coral nursery. In March 2021, offspring were transferred to the same in situ nursery or outplanted to reef plots either near to or far from (> 50 m) adult A. cervicornis to determine if proximity to other colonies affected parasite acquisition. Corals were sampled one week, one month, and two months post-transplantation to assess timing of Aquarickettsia infection and to examine shifts in the coral microbiome overall due to transplantation. We determined that proximity to wild or outplanted A. cervicornis influenced Aquarickettsia acquisition in outplanted conspecifics that lacked Aquarickettsia prior to outplanting. Only corals that were in close proximity to adult A. cervicornis acquired Aquarickettsia, and acquisition took between 1 and 6 months. Importantly, corals outplanted far from previously-extant outplants did not acquire Aquarickettsia by a full year after transplantation to the reef. This suggests that horizontal transmission is important in the acquisition of this putative parasite, and the parasite is likely transmitted by other A. cervicornis or reef organisms primarily associated with outplanted A. cervicornis (e.g. corallivorous snails, ciliates, bearded fireworms). We also observed that not all conspecifics from the same families acquired the parasite, even within the same site. This suggests that Aquarickettsia acquisition may require prolonged contact with a vector, or that there is an element of chance in exposure to and subsequent infection with Aquarickettsia.