Species Diversity and Distribution Patterns in the Mariana Back Arc Vent Fields

The Mariana Back Arc Spreading Center (BASC) is a partially enclosed basin that contains numerous hydrothermal vents. During the 2016 Hydrothermal Hunt cruise, the onboard team sampled four vent fields in the region, including the newly discovered Hafa Adai and Perseverance fields. These biological samples and video imagery expand taxonomic data from prior studies to explore the vent diversity patterns along the Mariana BASC, including four fields from the southern BASC over a total of 600km. We used morphological and/or molecular barcode analyses to determine the identities of both macrofauna and meiofauna. Four new species (gastropod, shrimp, barnacle and polychaete worm) resolved, and we document 12 additional taxa in the central BASC. While overall diversity is relatively low, three species of shrimp are present. With these data, we examine the beta diversity structure of fields along this spreading center. We used both the Jaccard and Raup-Crick beta diversity measures to identify the faunal dissimilarities among the Mariana BASC vent fields and to test possible processes driving these differences. Random assembly factors appear to dominate the dissimilarities, but deterministic factors likely impose a secondary influence. We compare beta-diversity patterns using similar analyses of vent species data from the adjacent Mariana Volcanic Arc and the Juan de Fuca Ridge. Both beta-diversity measures indicate that the species variability is much higher among the Mariana Arc vents than among either Mariana BASC or Juan de Fuca vents. Current work examines possible drivers of diversity distribution within this back-arc system, such as habitat size, isolation and fluid chemistry.