Trophic niches reflect compositional differences in microbiota among Caribbean sea urchins

Abstract

Sea urchins play a critical role in marine ecosystems, as they actively participate in maintaining the balance between coral and algae. We performed the first in-depth survey of the microbiota associated with four free-living populations of Caribbean sea urchins: <i>Lytechinus variegatus</i>, <i>Echinometra lucunter</i>, <i>Tripneustes ventricosus</i>, and <i>Diadema antillarum</i>. We compared the influence of the collection site, echinoid species and trophic niche to the composition of the microbiota. This dataset provides a comprehensive overview to date, of the bacterial communities and their ecological relevance associated with sea urchins in their natural environments. A total of sixty-samples, including surrounding reef water and seagrass leaves underwent 16S rRNA gene sequencing (V4 region) and high-quality reads were analyzed with standard bioinformatic approaches. While water and seagrass were dominated by Cyanobacteria such as <i>Prochlorococcus</i> and <i>Rivularia</i> respectively, echinoid gut samples had dominant Bacteroidetes, Proteobacteria and Fusobacteria. <i>Propionigenium</i> was dominant across all species' guts, revealing a host-associated composition likely responsive to the digestive process of the animals. Beta-diversity analyses showed significant differences in community composition among the three collection sites, animal species, and trophic niches. Alpha diversity was significantly higher among <i>L. variegatus</i> samples compared to the other species. <i>L. variegatus</i> also displayed an increased abundance of Planctomycetes and Cyanobacterial OTUs. The bacterial community of this herbivorous echinoid reflected similarities to the microfilm community found on <i>Thalassia testudinum</i> leaves; a very abundant seagrass and its main food resource. The results of this study elaborate on the microbial ecology of four important Caribbean echinoids, confirming that selection on the microbial community is trophic-niche dependent.