Fish-assemblage dynamics in Malibu Lagoon, a small, hydrologically altered estuary in southern California

Malibu Lagoon, California, USA, is a small estuary that has been substantially altered by habitat loss and increased freshwater input from development in its watershed. The lagoon's fish assemblage was sampled at nine stations on 32 occasions between July 1993 and August 1994 on at least a monthly basis using beach seines and fish traps. Thirteen fish species represented by 16,444 individuals were collected. California killifish (Fundulus parvipinnis) was by far the most abundant species, comprising 80% of the total catch. Mosquitofish (Gambusia affinis) constituted 9% of the catch, and topsmelt (Atherinops affinis) constituted 7%. As with other temperate estuarine fish assemblages, species richness and abundance varied seasonally, with peaks during summer. The majority of fish collected were juveniles, with topsmelt and California killifish recruitment being extremely high during some periods. Fish use of the portion of the lagoon restored as a salt marsh ten years prior to our study was evaluated. Fish species richness, density, and composition in the restored salt marsh were quite similar to those in the main lagoon as well as other natural salt marshes in southern California. Malibu Lagoon's species richness is low relative to some other southern California wetland systems, particularly large estuaries with uninterrupted tidal flushing, but is comparable to other southern California estuaries with similar hydrology. Despite extensive anthropogenic modification, Malibu Lagoon provides suitable habitat for a variety of fish species.