IV-D-19 



Warme, J.E. 1969. Mugu Lagoon, coastal California: origin, sediments, 



and productivity. Pages 137-154 in^ A.A. Castanares, ed.. Coastal lagoons, 

 a symposium. Universidad Nacional Autonoma de Mexico, Ciudad Universidad. 



The geomorphic development, sediments, flora, and fauna of Mugu 

 Lagoon (a shallow coastal lagoon in southern California) are investigated. 

 The lagoon can be divided into several morphologically distinct suben- 

 vironments, including the barrier beach, the inlet-tidal delta system, 

 tidal channels, ponds, tidal flats, tidal creeks, marsh, and salt pans. 



Plant species of the salt marsh fringing the lagoon are zoned pri- 

 marily by tidal levels and secondarily by sediment type and drainage 

 characteristics. Twelve marsh halophyte genera are common: Atriplex , Batis , 

 Distichl is , Frankenia , Timonium , Monanthochloe , Salicornia , Suaeda , Jaumea , 

 Triglochin , and Arthrocnemium . Spartina is also present, but much less 

 abundant than in certain other marshes along the California coast. 

 The lowest growth is at about the level of mean-lower high water. Most 

 Pacific coast marshes become established at about this level regardless 

 of the local tide range, suggesting that total submergence is critical 

 to marsh establishment. The low marsh is designated as that zone where 

 only Spartina fol iosa , Salicornia bigelovii , and Salicornia pacif ica are 

 abundant. This vertical interval of about 0.4m is inundated by the tides 

 at least once daily. At about 1.4m (MLHW), nine halophyte species become 

 well established, and they range upward to 1.8m or more. The upper marsh 

 occupies the vertical range from 1.8 to at least 2.1m. 



Rich vegetation, abundant benthonic invertebrates, and large popula- 

 tions of vertebrates living in Mugu Lagoon suggest increased organic 

 productivity relative to coastal v;aters immediately offshore. It is un- 

 likely that this productivity is dependent upon phytoplankton production. 

 Plankton hauls made in the lagoon were similar in species composition 

 and abundance to those made offshore, and these organisms were probably 

 transported into the lagoon by exchange of tidal waters. The high organic 

 productivity of shallow coastal lagoons is probably due to a characteristic 

 set of conditions prevailing in these regions. Organic matter is produced 

 by diatoms and other algae, eelgrass, and marsh plants. The same mechanisms 

 that concentrate mud in protected locations also operate to concentrate 

 organic matter as these plants die. The mud tends physically and chemically to 

 bind organic matter and serves as a substrate for abundant bacteria. 

 Microbial decay provides basic nutrients for continued primary productivity, 

 organic debris for detritus eaters, and an abundance of bacteria, which 

 is perhaps an important food source. These processes all take place within 

 the photic zone. There is no lag as in deep water, where nutrients 

 released on the bottom must be brought into the photic zone before they 

 can be fixed by photosynthesis and utilized by higher trophic levels. In 

 shallow, restricted areas, relatively greater productivity may result because 

 organic matter is concentrated and the carbon cycle is accelerated. (J.B.) 



Keywords: productivity, estuaries, salt marshes, California 



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