Los Osos Estuary
Map SatelliteThis area is a comparatively small but biologically significant portion of Morro Bay which is one of the very few shallow bay and estuary complexes in Southern California that remains relatively unaltered. Los Osos Creek is a small, year-round stream flowing into the eastern part of the Bay. Most of the estuary is a meandering tidal channel.
Within the area several biotic communities are represented including a freshwater and a saltwater marsh, coastal scrub, and an estuarine community. Well over a hundred plant species are found here. The dominant species in the freshwater area are California bulrush, Scirpus californicus, cattail, Typha latifolia, and arroyo willow, Salix lasiolepis. Pickleweed, Salicornia virginica, predominates in the salt marsh. Coyote brush, Baccharis pilularis, black sage, Salvia mellifera, California sagebrush, Artemisia californica, and coast live oak, Quercus agrifolia, are common on the stabilized sand dunes. These dunes, adjacent to the salt marsh, date from the late Pleistocene. In the estuarine area, various algae of the genera Ulva, Ulothrix, Enteromorpha, and Cladophora are common.
More than 25 species of mammals have been recorded in the area, including 8 species of mice and the endangered Morro Bay kangaroo rat, Dipodomys heermanni morroensis. Over 150 species of birds have been sighted in the vicinity. The California clapper rail, Rallus longirostris obsoletus, an endangered species, has been observed in this area in the past, but there have been no recent sightings. Fifteen different species of reptiles and ten amphibians have been reported in the area. Their occurrence ranges from rare to common, depending upon the species. Among the more unique records are the spotted night snake, Hypsiglena torquata, western rattlesnake, Crotalus viridis, and the western whiptail, Cnemidophorus tigris.
A dozen fish are common to the area and include both freshwater species such as the riffle and prickly sculpins, Cottus gulosus and Cottus asper, and marine species such as the starry-eyed flounder, Platichthys stellatus, topsmelt, Atherinops affinis, and shiner perch, Cymatogaster aggregata, as well as species inhabiting the transitional area between the fresh and salt water.
Shell middens are present which indicates an area of intensive Chumash Indian occupation.
Integrity: Zoned for light agriculture, there has been some channelization of the freshwater stream to improve and create pastureland and portions of the scrub have been bulldozed, but most of the area is relatively undisturbed.
Use: Research, education. A number of central California educational and scientific agencies utilize this and other portions of Morro Bay for class work and research.
Ref: Richards, Thomas L., 1972. Proposed Los Osos Wildlife Preserve. (Mimeo.) Unpublished.
January 1975
Inventory of California Natural Areas
Revision © 2009 Steven Louis Hartman
