ECOLOGY AND ENDOSYMBIONT DIVERSITY OF SIX CO-OCCURRING BIVALVES (BIVALVIA: LUCINIDAE) FROM AN ANTHROPOGENICALLY-IMPACTED TIDAL FLAT ON SUGARLOAF KEY, FLORIDA KEYS

Lucinids are chemosymbiotic bivalves that harbor putative sulfur-oxidizing bacterial endosymbionts within their gills. Endosymbionts are acquired from a free-living population sourced from coastal marine sediments, typically associated with vegetation like seagrass. Past studies have focused on characterizing the endosymbiont population in specific lucinid host species using 16S rRNA gene sequence analyses or metagenomics, but few studies have investigated the endosymbiont populations among multiple taxa living within one habitat location. To fill this gap in our understanding, the goal of this study was to analyze the endosymbiont diversity from six different taxa, Ctena orbiculata, Codakia orbicularis, Lucinisca nassula, Anodontia alba, Parvilucina pectinella, and Radiolucina amianta, collected from a tidal flat at Sammy Creek Landing on Sugarloaf Key in the Florida Keys (USA). Lucinids were collected every ten meters along two 50-m long transects perpendicular to the shoreline. Sediment and porewater samples were obtained to investigate sediment characteristics and the environmental bacterial diversity. Total nucleic acids were extracted from tissue and environmental samples, and bacterial 16S rRNA genes were amplified and sequenced using Illumina MiSeq. Resulting sequences were analyzed with MOTHUR using the Silva 102 database to assign operational taxonomic units (OTUs). Four of the six lucinid taxa (C. orbiculata, C. orbicularis, L. nassula, and A. alba) possessed the same dominant bacterial OTU at 97% sequence similarity levels, which was most closely related to the genus Sedimenticola. The lucinid hosts P. pectinella and R. amianta each had different dominant bacterial OTUs, which were also closely related to Sedimenticola spp. The second most dominant OTU in all the lucinids was most closely related to Sedimenticola spp. except for L. nassula, which had an OTU most closely related to Oceanospirillales. The variation between taxa could be attributed to variable vegetation coverage or the free-living population present in the water and sediment. By characterizing the bacterial diversity of multiple lucinid taxa at one location, important insights will be gained on the community dynamics in a coastal seagrass habitat.