Seamounts and Banks
Figure 1. Zones of seamounts and banks within the Monterey Bay, Gulf of the Farallones, and Cordell Bank National Marine Sanctuaries. [View Larger]
By contrast, seamounts are mainly volcanic in origin, rise a considerable height from great depths on the continental rise and are limited in length across the summit.
Despite their differences in scale, both banks and seamounts are isolated in space and have higher elevation and a different substrate than the surrounding seabed. Their vertical structure, habitat complexity and rocky substrate support a very different biological assemblage than the soft bottom that typically surrounds them.
Because these rocky features extend up into the water column, they provide ideal habitat for attached sessile invertebrates that depend on currents to deliver their food. The hard substrate is also favorable for settlement of larvae from the water column.
Cordell Bank
Cordell Bank is the centerpiece of Cordell Bank National Marine Sanctuary. It is approximately 7 kilometers (4.3 miles) wide and 15 kilometers long and sits on the edge of the continental shelf. Shelf depths at its base are about 91 meters (300 feet), with upper pinnacles reaching to within 35 meters of the ocean surface.The bathymetry and location of Cordell Bank combine to make it a very productive marine environment. Nutrients and productivity emanating from an upwelling center near Point Arena are carried over the bank and sustain a thriving biological community. Localized upwelling may also contribute to productivity.
The top of Cordell Bank is an invertebrate-covered reef crest. A cloud of juvenile rockfish hovers above.
Bubble gum coral (Sibogagorgia cauliflora) on the Davidson Seamount at 2502 meters. Species new to science; described in 2010 by Herrera, Baco, and Sanchez (Holotype: USNM 1122229). Credit: NOAA/MBARI 2006
Davidson Seamount
In March of 2009, NOAA designated the Davidson Seamount Management Zone (DMSZ), increasing the Monterey Bay National Marine Sanctuary (MBNMS) and protecting Davidson Seamount, making it the first seamount within a national marine sanctuary. Several other seamounts - including Gumdrop, Pioneer, and Guide Seamounts - occur just beyond Monterey Bay National Marine Sanctuary.Davidson Seamount is located 120 kilometers southwest of Monterey. This inactive volcano is approximately 2,300 meters tall and 42 kilometers long, yet its summit is far (1,250 meters) below the ocean surface.
Inhabitants
On Cordell Bank, sponges, hydrocorals, tunicates, anemones, gorgonians, solitary corals and hydroids compete for space on the upper-reef areas. More mobile animals like decorator crabs, sea stars, sea cucumbers, snails and demersal fishes move over the invertebrate carpet.This living reef also provides critical habitat for first-year juvenile rockfishes (Sebastes spp.) that settle out of the water column as they transition from a pelagic to benthic life stage. Adult rockfishes, lingcod and other benthic fishes also inhabit the complex habitats within the structure of Cordell Bank. The most conspicuous invertebrates occurring in the deeper reef areas include octopus, crinoids, white plumed anemones, sea stars and tube polychaetes.
Davidson Seamount's rocky outcrops, particularly near seamount peaks, are inhabited by a suite of deep-sea corals and sponges that are typically absent or quite rare in more typical ocean settings. Sea stars, anemones, crustaceans, octopus and fishes are common there. Recent explorations have discovered several species new to science.
Conservation and Management Issues
Activities that currently have the greatest potential impact on Cordell Bank are the use of bottom-tending fishing gears, the deposition of lost fishing gear and other marine debris, the introduction of invasive species, and the construction and placement of cables and pipelines on the bank.Davidson Seamount appears to be relatively pristine, based on observations of biological communities during submersible explorations. This contrasts with observations of various other seamounts worldwide, which have been subject to severe damage by trawling.
Monitoring
Currently there is one main study underway to develop a better understanding of the habitats and communities at and around Cordell Bank:Three studies have been conducted on two seamounts adjacent to Monterey Bay sanctuary: Davidson and Pioneer Seamounts. These include a characterization, coral distribution study and passive acoustic monitoring.
