Estero De San Antonio

Estero de San Antonio, along with the neighboring Estero Americano, are the best remaining examples of linear estuaries in California. The latter is considerably larger. Estero de San Antonio has approximately 55 hectares (90 acres) of open water and 80 hectares (200 acres) of wetlands. During the summer months a sand bar cuts the estuary off from the sea. When the estuary is open, tidal influence occurs some 5.5 kilometers (3.5 miles) upstream.

Virtually all of the wetland is a seasonally brackish marsh, with pickleweed, Salicornia virginica, Jaumea carnosa, salt grass, Distichlis spicata, the major components. The tule, Scirpus americanus, occurs here and, intermittently, along the upland margins of the mudflats. There is no naturally occurring freshwater marsh in the estero, but two small ponds have been constructed which have some marsh vegetation. There is a small grove of California bay, Umbellularia californica, in the area.

To the south of the mouth there is a rocky coastal bluff community which includes several ferns and various herbs such as Angelica hendersonii, Cerastium arvense, Dudleya farinosa, Erigeron glaucus and Sedum spathulifolium. Between the bluffs and the water there is a sandy area which supports a coastal strand community that is much richer than the strand community at Estero Americano. Here, 47 species have been recorded, including non-natives Cakile maritima, Ammophila arenaria and the natives Poa douglasii, Abronia latifolia, Cryptantha leiocarpa and Phacelia californica.

In the estuary, pondweed, Potamogeton pectinatus, and Ruppia maritima, occur in the brackish and freshwater areas. Eel grass, Zostera marina, is found near the mouth. Twenty-six species of marine algae have been collected in this estuary; only three are also found in the Estero Americano, 3 kilometers (2 miles) to the north. Mudflats occur at the mouth and up to 1.6 kilometers (l mile) inland.

A variety of animal life is present in the area. Birds are the most conspicuous; more than 100 species have been observed, over half waterfowl or shorebirds. Cinnamon teal, Anas cyanoptera, and mallards, Anas platyrhynchos, breed here.

Of the 24 species of fish that have been collected in this estuary, 10 have not been collected in the Estero Americano; this may be the result of different collecting times and methods. Topsmelt, Atherinops affinis, three-spined stickleback, Gasterosteus aculeatus, and bay pipefish, Syngnathus leptorhynchus, are among the species found here.

Stemple Creek is the main source of fresh water. The estero is a drowned valley.

Integrity: Cattle have had an impact on portions of the area but the estuary is virtually pristine.

Use: Private

Ref: Madrone Associates, 1977. The Natural Resources of Esteros Americano and De San Antonio. Calif. Dept. of Fish & Game, Coast. Wet. Ser. No. 20, 81+ pp.

February 1978