South San Francisco Bay National Wildlife Refuge

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South San Francisco Bay National Wildlife Refuge

Four main habitat types are found in this Refuge which covers much of South San Francisco Bay. They are salt marsh, 1,363 ha. (3,368 a.), mudflats, 2,672 ha. (6,602 a.), salt ponds, 3,857 ha. (9,531 a.), and open water, 836 ha. (2,066 a.), plus 12 ha. (30 a.) of uplands.

Man-made salt ponds occupy over 40% of the Refuge and are an important habitat. The flora is primarily algae, dinoflagellates and a unique bacterium. (See Greco and Bair Island Units). Rich concentrations of plankton are found in the ponds, and during the late spring and early summer there are huge populations of the commercially farmed brine shrimp, Artemia salina. A few fish tolerate the high salinities, namely, the mud-sucker, Gillichthys mirabilis, and topsmelt, Atherinops affinis. Diving ducks, grebes, phalaropes, shorebirds and certain gulls prefer the higher salinities; dabbling ducks, coots and fish-eating birds, the lower.

Tidal mudflats, varying in composition from soft, soggy mud to sand, shells and fine gravel, support immensely rich populations of molluscs, crustaceans, various worms, zoo- and phytoplankton. The vegetation is primarily algal, with sea lettuce, Ulva lacyuca, prominent.

In the salt marshes the dominant vegetation is cord grass, Spartina foliosa, pickleweed, Salicornia virginica, salt grass, Distichlis spicata, alkali heath, Frankenia salina, sea lavender, Limonium californicum and sea blite, Suaeda taxifolia.

In the open water, algae are present. Eel grass, Zostera marina, was common until its elimination by water pollution. The sloughs include several habitats and occur throughout the Refuge.

Over one hundred species of water birds have been reported, and on a day in the peak season the number of individuals may exceed 800,000. Additionally, some 50 species of land birds have been sighted in the Refuge.

A number of fish inhabit the area at some stage in their life cycle; among the more noteworthy are the white and green sturgeons, Acipenser transmontanus and Acipenser medirostris, several sharks and rays. Historically, the Refuge contained important oyster beds, Ostrea lurida and the exotic Ostrea virginica, which formed the basis for a thriving industry. After suffering severe declines from pollution, the molluscs (and various crustaceans) are making a comeback.

Geologically, the Bay is a Pliocene structural depression drowned by rising waters during the Pleistocene. In the southern portion, alluvial deposits left by Coyote Creek as it flowed north to join the main Sacramento-San Joaquin River near the embouchment at the Golden Gate have created a broad shallow-water area as well as the surrounding plains.

The Refuge is divided into four management areas, three contiguous on the east and south and one separate on the west.

Integrity: The salt ponds are drained and diked marshes, which can be reconverted. Powerlines, miscellaneous buildings and developments are common. Water pollution, which peaked in the 1960's, is on the downgrade.

Use: Research, educational, observational, light recreational.

Ref: Gill, Robert, 1972. South San Francisco Bay Breeding Bird Survey, 1971. California Department of Fish and Game, Sacramento. Mimeo. 68 pp. Fisler, G. F. 1965. Adaptations and Speciation in Harvest Mice of the Marshes of San Francisco Bay. Univ. Calif. Pub. Zoo. Vol. 77 (l), pp. 1-108.

December 1975