Intellectual Merit. Severe technical challenges associated with the extremes of hydrostatic pressure have prevented major advances in hadal ecological studies, and relegated hadal systems to among the most poorly investigated habitats on Earth. The recent development of the fully functional Hybrid Remotely-Operated Vehicle Nereus has now prompted scientists from around the world to join together to identify the foremost standing questions in hadal science. Through this project, Hadal Ecosystems Studies (HADES) program, PIs from 7 Institutions from around the world will determine the composition and distribution of hadal species, the role of hadal pressures (piezolyte concentrations, enzyme function under pressure), food supply (distribution of POC with the abundance and biomass of trench organisms, and metabolic rates/energetic demand), and depth/topography (genetic divergence and spatial connectivity of populations) have on impacting deep-ocean community structure. This project will examine these factors using the world's first full-ocean depth hybrid remotely operated vehicle (HROV) in conjunction with the only full-ocean depth imaging lander (Hadal-Lander). This will pose a comparative framework for investigating hadal and abyssal community structure as driven by pressure (and associated factors), food supply, physiological adaptations, and topographic relationships. The investigators' first order hypotheses to explain how faunal diversity and communities are structured in trenches completely lack the data necessary to test them. Thus this project will provide the first seafloor data and samples in one of the world's best, yet little known trenches- the Kermadec Trench (SW Pacific Ocean). The first international Trench Connection Symposium in 2010 concluded the need to identify patterns of trench faunal composition and understand the first order factors that play a role in structuring these ecosystems. Megafaunal community structure and the relationship between POC and benthic bacterial biomass will be examined as a function of depth and location by systematic high-definition imaging and sediment/faunal sampling transects from abyssal to full trench depths both along and perpendicular to the trench axis. Population genetic approaches will provide levels of genetic divergence and evolutionarily independent lineages to assess the role of depth and topography in trenches and their adjacent abyssal plain in promoting the formation of species. Physiological constraints will be investigated by examining in-situ respiration of selected fauna and tissue concentrations of such protein stabilizers as trimethylamine oxide (TMAO), and the structural adaptations of macromolecules. These objectives represent an achievable and powerful combination of current technological capability, scientific understanding and theory, and the expertise of an international consortium of scientists. Broader impacts. The project will direct new avenues of research in the deep ocean. The expedition and results will be disseminated broadly to the scientific community and the public through both active metadata and data sharing mechanisms, award winning sea-going web-based education curricula and data-posting web portals, museum exhibits, and a major National Geographic television event featuring trench and deep-sea science, including life forms at the deepest depths on earth will engage the imagination of scientists and public alike. Outreach with respect to global scientific literacy will focus on the fundamental planetary processes associated with hadal faunal ecology and evolution at the world's deepest trenches. A daily-updated web site from sea will provide real-time public, museum, and aquaria access to the ongoing cruise activities and discoveries. The integral involvement of postdocs, graduate and undergraduate students will foster professional and educational advancement opportunities for underrepresented groups. In addition, we will stimulate a broader collective of interested biologists, chemists, geologists, and others to advance the application of ecological and evolutionary theory to better understand the biodiversity that inhabits hadal ecosystems. To this end, the investigators will develop an international consortium for hadal science dedicated to training the next generation of marine scientists and in conjunction with INDEEP, international collaboration for deep-sea research. The use of the HROV Nereus will advance this vehicle's capabilities for a broad range of disciplinary use, drive advances in applying technologies for conducting rigorous hadal and abyssal science, and further off-shoot technologies for use by the broader scientific community. The results of this project will be the first of its kind regarding the environmental variables that structure trench communities and lay the essential foundation for future work on the dynamic processes that create and maintain biodiversity in the deep ocean.