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Regional Overview & Fact Sheet
The Montereyan Pacific Transition Region, which stretches along the central California coast from Point Conception to Cape Mendocino (USA), has moderately high productivity associated with the seasonal upwelling that occurs along its coasts. Also found in the region is a series of very significant submarine canyons and seamounts, such as the Monterey Submarine Canyon—one of the largest on the Pacific coast of North America. Because of the canyon’s proximity to shore, deepwater species of whales, dolphins and seabirds are found near the coast. The region also takes in three major estuaries that serve as important habitats for many marine species. San Francisco Bay—the largest estuary in the region—is a major staging area for migratory birds in the Pacific Flyway, but also an area where more than 95 percent of the historic tidal marshes have been modified. Invasive species are also a major threat to the Bay’s biota. The keystone sea otter also makes its home within the region. The region includes two B2B Marine Priority Conservatiton Areas (PCAs): PCA 16-Central California, and PCA 17-Upper Bight of the Californias/Channel Islands/San Nicolas Island (Morgan et al. 2005).
Fact Sheet
Transitional between temperate and subtropical regions and faunas.
11–14°C (winter), 13–15°C (summer)
California Current and Davidson Current.
Very narrow shelf with major canyon systems in the slope and below.
shelf (roughly 0–200 m): 4%;
slope (roughly 200–2,500/3,000 m): 13%;
abyssal plain (roughly 3,000+ m): 83%
Sand and rock from Point Conception to Estero Bay; mud-sand and rock north to Monterey Bay; mud-sand sediments in San Francisco Bay; and mainly sandy north of San Francisco Bay.
Bays and estuaries, sandy beach and rocky intertidal communities, kelp beds, submarine canyon and cold seeps, deep sea and seamount communities, offshore island and bank communities.
The California Current is considered a moderately high productivity ecosystem (150-300 gC/m2-yr). The effects of coastal upwelling, ENSO and the Pacific Decadal Oscillation (PDO) result in strong inter-annual variability in the productivity.
Delta smelt and subpopulations of several Pacific salmon species.
Blue, fin, North Pacific right, humpback, gray and sperm whales; Steller sea lion; southern sea otter; California brown pelican; California least tern; marbled murrelet; pink-footed shearwater; short-tailed albatross; leatherback, loggerhead; delta smelt; steelhead, chinook and coho salmon; Pacific hake; cowcod and bocaccio rockfish; black and pinto abalone.
Over 234 species identified (San Francisco Bay, in particular), including Asian clam, compound sea squirt, Chinese mitten crab, and European green crab.
Tourism, fishing, commercial shipping, and coastal development.
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Physical and Oceanographic Setting
The Montereyan Pacific Transition Region consists of a very narrow continental shelf and steep continental slope, transected by a series of submarine canyons. Three major estuaries are found in northern and central California, within San Francisco Bay and Tomales Bay, and Elkhorn Slough. Shelf habitats are predominantly composed of soft sediments, although rocky areas are the most biodiverse. The deepest and largest submarine canyon on the coast of North America is the Monterey Canyon in the center of Monterey Bay. It is 470 km long, approximately 12 km wide at its widest point, has a maximum rim to floor relief of 1700 m, and serves as a major conduit for sediment transport from the continental shelf to the deep-ocean floor. Other major canyons include Bodega, Pioneer, Carmel, Sur and Lucia Canyons. Beyond the slope, Gumdrop, Pioneer, Guide, and Davidson Seamounts rise above the abyssal plain.
The California Current is the dominant current system affecting the region. A sub-surface poleward California Undercurrent flows along the continental slope, extends to the surface next to the coast from October through February and is referred to as the Davidson Current. In the winter, during periods of low stratification, the Southern California Countercurrent, Davidson and California Undercurrent can merge, and this seasonal northward flow helps account for this region’s transitional nature. Current fluctuations occur in association with El Niño events and basin-wide events (e.g., Pacific Interdecadal Oscillation). Within the California Current system, upwelling is most pronounced in this region, occurring off major capes, particularly between mid-February and mid-July.
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Biological Setting
The region represents a transitional zone between the subtropical species representative of southern California and Baja California, and the more northerly species. The major biogeographic affinities seem to be with the northern regions, but southern species often extend their ranges during ENSO events and warm phases of the Pacific Decadal Oscillation. The strong seasonal upwelling contributes to moderately high productivity.
This remarkably productive coastal environment is home to numerous mammals, seabirds, fishes, invertebrates and plants, such as giant kelp, krill, dungeness crab, rockfish, bonito, California skate, Pacific salmon, market squid, albatross, shearwaters, common murre, ashy storm-petrel, brown pelican, gulls, Steller sea lion, Dall’s porpoise, harbor seal, as well as gray, blue and humpback whales.
Coastal wetlands associated with estuaries support millions of shorebirds and waterfowl during spring and fall migrations, and over the winter months. These estuaries also serve as important spawning and nursery grounds for marine species. San Francisco Bay is the largest estuary in the region and is a major staging area for migratory birds in the Pacific Flyway, hosting roughly a million migratory and resident birds.
The region’s kelp beds are key habitats for numerous species. Giant kelp forms dense beds on rocky subtidal areas and bull kelp, which is the most abundant surface canopy kelp in California north of Santa Cruz, occurs from near Point Conception, California north to the eastern Aleutian Islands. Within this region, the southern sea otter is resident in areas between Point Conception and San Francisco Bay. The sea otter is regarded as a keystone species because of its significant influence in maintaining kelp forest communities, primarily through its predation on sea urchins, the dominant herbivore. Major northern elephant seal areas are found south of Cape Mendocino, with a large rookery at Ano Nuevo Point. Davidson Seamount is one of the largest seamounts on the west coast and has remarkable biological communities, including large, dense patches of sponges and extremely old gorgonian coral aggregations, with individuals commonly reaching more than 3 m in height.
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Human Activities and Impacts
The Montereyan Pacific Transition Region includes scenic coastlines and the San Francisco urban area—the second-largest urban population on the west coast of North America. The San Francisco Bay estuary is renowned for its natural beauty, international commerce, recreation, and sportfishing. However, more than 95 percent of the historic tidal marshes have been modified, with attendant losses in fish and wildlife habitat. The flow of freshwater into the estuary has been greatly reduced by water diversions largely to support irrigated agriculture. Harbor and channel dredging, including both activities undertaken during dredging for navigation and disposal of dredge spoils, disturb communities, alter water flow patterns and salinity. Contaminants also enter the estuary through municipal and industrial sewage, as well as urban and agricultural runoff. Phosphorus concentrations are high and sediment and fish contaminant conditions are poor (EPA 2005). Invasive introduced species are a major threat to the Bay's biota.
Fisheries in the region are important, but have suffered major declines. Numerous species, including rockfishes, sardines, salmon, sablefish, and abalones, have declined under pressure of commercial and recreational fishing. Some species, including lingcod, cowcod, bocaccio, canary rockfish, and Pacific ocean perch are overfished, and salmon and steelhead populations have been listed under the US Endangered Species Act.
In the US Pacific coast, that includes ecoregions 19, 20 and 21, six out of 48 federally managed stocks are overfished with 13 of unknown status (NMFS 2007).
Level II and Level III Descriptions
Level II captures the break between neritic (near shore) and oceanic areas and is determined by large-scale physiography (continental shelf, slope, and abyssal plain, as well as areas of oceanic islands and major trenches, ridges and straits). This level reflects the importance of depth as a major determinant of benthic marine communities as well as the importance of major physiographic features in determining current flows and upwelling. Like Level I, it extends from the coasts to the EEZ.
Level III captures differences within the neritic realm and is based on more locally significant variables (local characteristics of the water mass, regional landforms, as well as biological community type). Level III is limited to the continental shelf, since only this area has sufficient information for finer-scale delineation.
Level II and Level III Ecoregions
Other Marine Ecoregions
Marine ecoregions are areas of general similarity in terms of physiographic, oceanographic and biological characteristics, which fall within the Exclusive Economic Zones of the North American countries. There are 24 marine ecoregions in North America.
