Diversity and biogeography of Hadal Amphipoda

Abstract

he ocean’s deepest ecosystem, the hadal zone (> 6000 m), is comprised of 47 subduction trenches, non-subduction troughs, and trench faults. These geomorphologically-complex features have been considered to function as ecological and evolutionary independent units, because of extreme environmental conditions, long-term geographical isolation, and evolutionary selection pressures. The order Amphipoda has emerged as a model taxon for understanding the evolution of life and ecology in the hadal zone. Much progress has been made identifying the diversity and understanding the ecology within individual features. This work, however, has solely focused on deep, subduction trenches around the Pacific Rim, leaving shallower features and non-Pacific features underrepresented. This thesis aims to improve our understanding of the drivers of diversity and population and community structure among scavenging amphipods across the hadal zone. This body of work is executed through three lines of study, utilizing a specimen collection from 16 hadal features. The first line applied an integrative taxonomic approach to expand the known diversity of scavenging amphipods in the Indian and Pacific Oceans. This work has resulted in the description of Eurythenes plasticus, the world’s first new species described to be impacted by microplastics, Eurythenes atacamensis, a unique hadal dominate lineage in the Peru-Chile Trench, Stephonyx sigmacrus, the deepest known species of this genus, and Civifractura serendipia, a new cryptic genus and species within the Alicellidae family. The second line assessed how the community shifts across the abyssal-hadal transition zone in a non-subduction hadal feature, the Wallaby-Zenith Fracture Zone, Indian Ocean. The third line investigated the global distribution and phylogeography of Bathycallisoma schellenbergi between twelve hadal features in four oceans. Together, this thesis expands our knowledge of hadal communities to features beyond subduction trenches and contributes to the disentanglement of the environmental, tectonic, and other drivers of contemporary diversity across the hadal zone.