Seafloor mapping of the Santa Monica Basin, using both autonomous and robotic submersibles, has uncovered the existence of numerous mounds uplifted by vigorous methane gas bubbling and the resulting rock (carbonate) formation.
Their presence along the California coast may be associated with seismic fault activity, but scientists are still exploring this possibility. These mounds are visually spectacular, supporting communities of brightly colored bacteria, snails, and worms (our usual subjects). We previously visited one of these mounds in 2013 (at 863 meters depth) and amazingly we found the exact same marker we left on the seafloor back then, allowing us to take comparison samples to measure changes in the sediment microbial community over the last 7 years. While sampling, we were photo bombed by many interesting looking red jellyfish with large oral arms and thin tentacles around their bell.