The scientific objectives of the HADEX Program are to:
- Investigate the existence, constraints, limits, and evolution of life on Earth.
- Enable comparative investigations of life in hadal and neighboring abyssal regions.
Goal #1: Hadal and abyssal community structure
Compare the composition, abundance, and diversity of life from 4,000 to 10,000 meters at 1,000-meter intervals in trenches and adjacent abyssal plains around the world.
Hypothesis: Differences in hadal community structure occur as a function of depth and, in particular, between topographically distinct hadal trench and abyssal plain habitats.
Goal #2: Food supply
Quantify the distribution of particulate organic carbon and bacterial biomass in trench and abyssal environments and relate this to megafaunal distribution, density, depth, and topography.
Hypothesis: In the absence of pressure limitations, concentrations of both benthic bacteria and deposit-feeding organisms within a hadal trench should occur along the trench axis where resources are likely to accumulate.
Goal #3: Energetic demand and metabolic rates
Investigate physiological constraints to life in hadal regions by examining in-situ respiration of abyssal and hadal fauna at different depths and pressures.
Hypothesis: If food supply is a determinant of individual metabolisms, then we expect higher metabolic rates in animals found along the trench axis, regardless of depth.
Goal #4: Biochemical adaptation
Determine whether or not the depth range over which a species can live depends in part on pressure-counteracting osmolyte (piezolyte) concentrations in tissues.
Hypothesis: TMAO acting as piezolytes (as well as other stabilizing osmolytes) help organisms adapt to pressures in the deep sea, and the ability to accumulate such solutes may determine depth distributions of some organisms.
Goal #5: Genetic diversity
Examine the role in promoting the formation of new species of depth, topography, and habitat diversity along trenches and in adjacent abyssal plains.
Hypothesis: Depth and topographic differences between trench and abyssal environments have promoted the formation of genetically distinct species in each region, while population genetic divergences driven by depth and habitat diversity have resulted in hadal populations exhibiting greater genetic structure than those at abyssal depths.