Seafloor Environment

photo of sea stars and coral
Basket sea star in soft bottom habitat of Cordell Bank. Credit: NOAA

Continental Shelf

The continental shelf is the gradually sloping submerged part of the continent that extends from the shore to the shelf break. The boundaries of Cordell Bank National Marine Sanctuary include only the outer continental shelf, with depths of approximately 230 to 656 feet. The continental shelf makes up sixty-five percent of the sanctuary seafloor. The majority of the seafloor in the sanctuary is on the continental shelf, composed of sand and mud bottoms. Soft bottom associated species live either on the surface of, or buried in the sediments. Cordell Bank emerges from the soft sediments of the continental shelf at depths of 300 to 400 feet and reaches to within 115 feet of the ocean's surface.

Continental Slope

The continental slope makes up 190 square miles of the sanctuary (35% of the sanctuary seafloor) and extents from 656 feet down to 6,955 feet at the western boundary of the sanctuary. The slope environment is primarily mud bottom with some rock habitats. Little is known about the slope region within this sanctuary; however, several research submersible dives have been conducted on the upper slope between 656 and 984 feet. Fishes observed on the mud substrate include spotted ratfish, poachers, English sole, slender sole, stripetail rockfish, splitnosed rockfish, long-spined combfish, hagfish, and six-gilled shark. Aggregations of the fragile pink sea urchin are commonly observed on the mud bottom of the upper slope.

Submarine Canyons

Bodega Canyon cuts into the continental slope north of Cordell Bank. Over 5,200 feet deep, it extends from the continental shelf to the deep sea.  Several other small submarine canyons also cut into the continental slope of the sanctuary west of the Bank. Taken together, the walls and floors of these submarine canyons cover a small proportion of the seafloor within Cordell Bank National Marine Sanctuary. These canyons, which extend to greater depths beyond the sanctuary's western boundary, may provide refuge for important species of fish and provide a habitat for sensitive species of deep water corals and sponges. Present scientific knowledge about these canyons is limited as they are largely unexplored, but the majority of their habitats is expected to be soft-bottom, while a much smaller portion is predicted to be hard-bottom.

For more information on the continental shelfcontinental slope and submarine canyons within Cordell Bank National Marine Sanctuary and the research being conducted on these topics, please visit the Sanctuary Integrated Monitoring Network (SIMoN).