The mid-ocean 'twilight zone' holds the key to several tantalizing questions about the marine food web and carbon-sequestering capacity of the ocean. But studying this vast and remote area is extremely difficult. Many inhabitants of the twilight zone are easily destroyed during sampling -- or are quick to avoid any disturbance -- so it's difficult to sample them with traditional nets. Advances in acoustics have enabled more accurate estimates of biomass, but questions about the diversity and distribution of species within that biomass remain unanswered.