The reef fish assemblage of the outer Los Angeles Federal Breakwater, 2002-2003.

Publication: Bulletin (Southern California Academy of Sciences)

Publication Date: 01-AUG-05

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Abstract.--The conspicuous and cryptic fish assemblage of the Los Angeles Federal Breakwater was assessed from 2002 to 2003. Thirty-five species were observed or collected during the study period. The assemblage of cryptic fishes was composed primarily of a mix of Oregonian and San Diegan, species including snubnose sculpin (Orthonopias triacis), coralline sculpin (Artedius corallinus) and blackeye goby (Rhinogobiops nicholsii). The species composition of conspicuous fishes was approximately equal between taxa from these two provinces. Blacksmith (Chromis punctipinnis), black perch (Ernbiotoca jacksoni) and kelp bass (Paralabrax clathratus) dominated the assemblage of conspicuous fishes. Species composition reflects the localized cool temperature regime of the area and the high relief kelp forest habitat.

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Rocky reefs are among the most important but least abundant habitats within the Southern California Bight (Cross and Allen 1993). More than 125 species of fish have been documented in this habitat, more than 25% of the Californian marine total (Quast 1968b; Feder et al. 1974; Horn and Allen 1978). Artificial reefs have been constructed within the Bight to augment natural reefs and to mitigate lost natural reefs through development or habitat degradation (Ambrose 1994). Although not their primary purpose, breakwaters form artificial reefs and have been shown to be effective fish enhancement structures in urban areas (Stephens et al. 1994). Breakwaters provide high relief, complex habitats that are ideal for many reef-associated fishes. The Los Angeles Federal Breakwater is 13.8 km long (McQuat 1951) making it the largest artificial reef in the Southern California Bight, yet, prior to this study, a systematic characterization of the fish population on this breakwater has not been made. The breakwater at King Harbor, Redondo Beach, California has been extensively surveyed since 1974, and more than 100 species of fish have been observed with about half of those being resident (present year-round throughout the study) species (Stephens and Zerba 1981; Stephens et al. 1994). However, this breakwater is also characterized by a high degree of temperature stratification due to warm water input from a coastal generating station into King Harbor and its proximity to the Redondo submarine canyon. King Harbor, a small craft marina, is also probably less affected than Los Angeles Harbor, a major international port, by anthropogenic effects. Quantitatively evaluating the fish assemblage on Los Angeles Federal Breakwater will provide critical information on the potential of these structures to replace or supplement natural rocky reef habitat in an urban setting.

Artificial reefs have been shown to support high densities of fish due to either attraction or production of fishes, but generally have low standing stocks compared to natural reefs because artificial reefs are generally smaller than natural reefs (Ambrose and Swarbrick 1989; Demartini et al. 1989). Monitoring of reef fishes has become an important component of many fisheries management strategies to ensure maintenance of "healthy" ecosystems and sustainable fisheries (Stephens and Zerba 1981; Stephens et al. 1984; Paddack and Estes 2000). This task is especially important in areas that are near large population centers and/or are heavily influenced by anthropogenic activities.

Visual censuses along transects with defined widths and lengths can be used to make reasonably accurate estimates of the density of fishes, and their effectiveness has been well established for fishes on temperate reefs in southern California (e.g. Quast 1968a, b, c; Ebeling et al. 1980; Stephens and Zerba 1981; Larson and DeMartini 1984; Stephens et al. 1986; DeMartini et al. 1989; Allen et al. 1992). However, visual censuses tend to underestimate fish densities (Sale and Douglas 1981) especially those of small or cryptic species (Brock 1982; Bellwood and Alcala 1988). These limitations are generally well recognized and do not prevent reasonably precise density estimates for conspicuous fishes from being obtained.

Cryptic fishes are usually small, camouflaged fishes that live in or among rocks, crevices, or algae. These fish usually retreat into the reef in the presence of divers and thus cannot be accurately sampled using techniques for estimating densities of conspicuous fishes. Cryptic fishes are more precisely estimated with the use of ichthyocides or anesthetics (Allen et al. 1992). Previous studies in southern California have shown cryptic fishes to be important members of rock reef habitats in terms of density, species richness (Allen et al. 1992), and secondary productivity (Stephens and Zerba 1981; Stephens et al. 1984).

The primary goal of this study was to provide a description of the reef fish assemblage of the outer Los Angeles Federal breakwater using visual census and an anesthetic to survey both large mobile and small cryptic fishes effectively. The densities, depth distributions, biomass and seasonality of the fish assemblage were determined.

Methods

The Los Angeles Federal Breakwater forms the western border of the Los Angeles-Long Beach Harbor complex (Figure 1). The Breakwater was constructed in three parts. The northernmost section was completed in 1912 and the final two sections were completed in 1928 (McQuat...

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