South San Diego Bay

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South San Diego Bay

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Unique among California bays, South San Diego Bay is essentially a hypersaline lagoon resembling the coastal lagoons on the Gulf of Mexico. The relative shallowness reduces the tidal flushing action, and during the warmer months the water temperatures and salinities are greater than those in the open ocean, though in the winter months they are comparable. The marshes and mudflats were formed by the sediments brought down by the rivers and creeks that emptied into the Bay. Approximately 10% of the once extensive salt marshes remain today, scattered in 0.8-hectare (2-acre) to 80-hectare (200-acre) plots around the Bay's periphery. The largest are found in the Sweetwater River-Paradise Creek and Otay River areas.

Plant communities range from sublittoral to a modified coastal sagebrush. In the sublittoral there are extensive beds of the algae Gracillaria verrucosa and Chaetomorpha spp. The mudflats are generally barren though along the upper edges are mats of Enteromorpha sp., Cladophora sp., Ulva sp., and other green algae. In the littoral zone the lowest community (MLHW-MHHW) is dominated by dense stands of cord grass, Spartina foliosa, with the pickleweeds, Salicornia bigelovii and Salicornia virginica, as subdominants. Between MHHW and extreme high water, Salicornia virginica dominates, with Salicornia bigelovii, Batis maritima, arrow grass, Triglochin maritima, and alkali heath, Frankenia salina, present. At slightly higher elevations, sea blite, Suaeda californica, appears in the association along with marsh lavender, Limonium californicum, salt marsh grass, Distichlis spicata and Jaumea carnosa. Three rare plants have been collected in the area, Erysimum ammophilum, Lotus nuttallianus, and Frankenia palmeri; the latter is known from only this locality in California but occurs in Baja California and Sonora.

The Bay and the adjacent coastal waters constitute one of the major Pacific flyway wintering grounds. Within the Bay, 99 species of birds have been observed. Various birds breed on the dikes bordering the salt ponds, including the only elegant tern, Thalasseus elegans, breeding colony in the United States and one of the two Forster's tern, Sterna forsteri, breeding areas in Southern California. At least three endangered birds are found here, brown pelican, Pelecanus occidentalis californicus, California least tern, Sterna albifrons browni, and the light-footed clapper rail, Rallus longirostris levipes, the latter two as breeders.

At least 22 species of fish are found in the shallow South Bay. The California killifish, Fundulus parvipinnis, and striped mullet, Mugil cephalus, frequent the marshes.

A number of larger invertebrates, including nemertean and polychaete worms, molluscs, crustaceans, isopods, etc., have been recorded in the area, with the snail, the California horn shell, Cerithidea californica, conspicuously abundant.

Integrity: Most of the marsh has been filled and developed, the mudflats dredged or converted to salt ponds; filling continues. Water pollution, once severe, is diminishing.

Use: Research, educational, observational, salt ponds.

Ref: Browning, B. and J. W. Speth, 1973. The Natural Resources of San Diego Bay; Their Status and Future. Calif. Dept. of Fish and Game Coast. Wetland Series #5, Sacramento, 105 pp. plus appendix.

December 1975