Deeper than most scuba divers can safely work and above where most underwater robots are designed to descend lie some of the most poorly studied ecosystems in the world. Between 30 and 150 meters down is the ocean's mesophotic zone, meaning middle-light. Communities of life exist here at the limit of where photosynthesis can occur. On rocky surfaces in the cold water, seaweeds slowly give way to sponges, anemones, and sea squirts—small tube-like creatures that filter plankton from the water.