It is estimated that there are more than 30,000 seamounts in the world’s oceans, including numerous volcanic seamounts offshore of California. Davidson Seamount is located 120 kilometers (75 miles) to the southwest of Monterey, 150 kilometers (93 miles) west of Cambria, and is one of the largest known seamounts along the western United States. (See Figure 1.) It is 42 kilometers long and 13.5 kilometers wide. From base to crest, Davidson Seamount is 2,400 meters tall; yet it is still 1,250 meters below the sea surface. It has an atypical seamount shape, created by a type of volcanism only recently described by geologists; it last erupted about 9.5 million years ago.

Figure 1. Davidson Seamount and the southern portion of the sanctuary. image C. King

Exploration history of the Davidson Seamount is simple, yet notable. The seamount was first mapped in 1933. This large geographic feature was the first to be characterized as a "seamount" in 1938 and was named in honor of George Davidson (1825-1911), a leader in charting West Coast waters. During the 1970s rock samples were collected to study the seamount’s geology. Sonar mapping techniques improved geologic images during the 1990s, and recently, remotely operated vehicles (ROVs) have provided more precise collection devices and photo images of the seafloor, associated biology, and surrounding water column.

Figure 2. Bamboo coral (Keratoisis sp.), like this one at 1,452 meters below the surface, have been aged to greater than 200 years. photo NOAA/MBARI

During May 2002 a multi-institution expedition, led by the Monterey Bay National Marine Sanctuary, characterized the distribution and abundance of organisms at the Davidson Seamount. (See Ecosystem Observations 2002, p. 9.) The sanctuary partnered with the Monterey Bay Aquarium Research Institute (MBARI), Monterey Bay Aquarium, Moss Landing Marine Laboratories (MLML), and the National Oceanic and Atmospheric Administration (NOAA) Fisheries to explore the seamount using MBARI’s Research Vessel Western Flyer (Figure 3) and ROV Tiburon. The ROV traversed a bottom distance of 43,537 linear meters and recorded ninety hours of digital video imagery. In addition, a bird and mammal survey was conducted at the sea surface, and approximately 255 species were identified. With these and other data from MBARI, Davidson Seamount is one of the best mapped and biologically characterized seamounts in the world.

Figure 3. During May 2002 a multi-institution expedition explored the seamount using MBARI's Western Flyer. photo NOAA/MBARI

Figure 4. Several undescribed sponges were observed, including this mushroom-like sponge (Caulophecus sp.) at 1,949 meters. photo NOAA/MBARI

Several spectacular habitats can be found on the seamount. The surface waters above it host a variety of seabirds, marine mammals, and surface fishes, including albatrosses, shearwaters, jaegers, sperm whales, killer whales, and ocean sunfish. From the sunlit surface waters to the top of the seamount lies a vast, three-dimensional habitat known as the midwater. Organisms here include the big red jelly, an undescribed mollusk, and tomopterid worms. The greatest diversity can be found at the seamount crest (~1,250-1,500 meters below the surface), including forests of large bubblegum coral (Paragorgia sp.), vast sponge fields, crabs, deep-sea fishes, and basket stars. The slope habitat (~1,500-2,500 meters below the surface) is com-posed of cobble and rocky areas interspersed with shallow areas of ash and sediment. This area hosts a diverse assemblage of sessile invertebrates and seldom-seen deep-sea fishes. The interface between rocky outcrops and the deep soft bottom is a distinct base habitat (~2,500-3,250 meters below the surface) for mobile animals. These organisms consist of familiar-looking species with relatives living in the nearshore, including cucumbers, urchins, anemones,and sea stars.

The Davidson Seamount exhibits high coral abundance and diversity and is a relatively pristine area. Twenty coral species were observed and located almost exclusively on seamount ridges (1,248-2,846 meters below the surface). Many of the corals are large and fragile to physical disturbance. Researchers at MLML determined age estimates for two coral species ranging from 115 years (precious coral, Corallium sp.) to greater than 200 years (bamboo coral, Keratoisis sp.; see Figure 2). Habitat and species analyses will be used to characterize the area, provide information for resource managers, educate the public, and further the advancement of seamount research.

This research on Davidson Seamount has received more public attention than any other sanctuary research effort. National television news, in-flight airline news, newspapers, radio programs, newsletters, an interactive educational compact disc, and several web sites highlighted results and activities from the cruise. The compact disc, "Exploring Davidson Seamount," is available for purchase through the Monterey Bay Sanctuary Foundation. Readers can share the excitement by visiting the Sanctuary Integrated Monitoring Network (SIMoN) web site (www.mbnms-simon.org/sections/seamounts/overview.php?sec=s). The sanctuary is formally assessing the option of providing national marine sanctuary status to the Davidson Seamount.

The Sanctuary Advisory Council unanimously supported its designation so long as current fishing activities in the area were not impacted. While no bottom trawling currently takes place at depth, sanctuary designation will help preserve the fragile resources on the seamount by protecting them from any future expansion of trawling effort. It will also ensure that impacts from bioprospecting and scientific collection are minimized, through the use of the sanctuary’s permitting system. Currently, there are no government education programs broadly focusing on seamount biology, and the designation of a seamount would therefore represent a unique opportunity for education and outreach. A draft environmental impact statement for the sanctuary’s revised management plan will be available in the early summer of 2005 and will analyze alternatives for seamount designation and protection. A final decision is expected in 2006.

Erica Burton and Andrew DeVogelaere
Monterey Bay National Marine Sanctuary