appendix b final 2008 biological surveys of los angeles and long ...

5.0 Benthic and Epibenthic Invertebrates
5.3.2 Taxonomic Composition and Dominant Taxa
The infaunal community was numerically dominated by polychaetes (48% of annual mean
abundance), crustaceans (31%), and molluscs (20%) (Table 5.3-2). Echinoderms (2%) and
other minor phyla (2%) were substantially less abundant. Molluscs and polychaetes accounted
for most of the infaunal biomass (Table 5.3-3). Polychaetes were the most diverse taxonomic
group (123 species), followed by molluscs (64 species) and crustaceans (51 species) (Table
5.3-4). The substantial decline in abundance between summer and winter, a pattern noted in
Section 5.3.1, was primarily associated with a decline in crustacean abundance (Appendix E).
The non-indigenous semele clam (Theora lubrica) was the most abundant species in the Los
Angeles-Long Beach harbor complex, accounting for approximately 10% of the total abundance
of infauna collected in the harbors (Table 5.3-5). Other dominant species, each accounting for
approximately 2.5 to 6% of the total abundance, included a leptostracan crustacean (Nebalia
pugettensis-complex), an amphipod crustacean (Amphideutopus oculatus), a pea crab
(Scleroplax granulata), and polychaete worms (Cossura sp. A, Monticellina siblina [reported as
Tharyx sp. in previous studies], Pisa agassizi, Pseudopolydora paucibranchiata, Streblosoma
sp. B). Most of these species have been numerical dominants in previous studies of the
harbors (HEP 1976, 1980; MBC 1984, MEC 1988, MEC 2002).
Several of these species were relatively widely distributed, although abundance levels varied
among stations (e.g., Aphelochaeta petersenae, Cossura sp. A, Monticellina siblina, Pista
agassizi, Streblosoma sp. B, Scleroplax granulata, and Theora lubrica) (Appendix E). Other
dominant species with relatively widespread distribution included the amphipod Eochelidium sp.
A and the polychaete Pista wui.
In contrast, a few species were more restricted in distribution by depth or location within the
harbors. For example, Amphideutopus oculata and Pseudopolydora paucibranchiata were most
abundant in shallow water (Stations LA2, LA3, LA7, LB2). Nebalia pugettensis-complex was
most abundant in the Consolidated Slip in inner Los Angeles Harbor (Station LA14).
5.3.3 Spatial Patterns of Abundance
Results of cluster analysis investigating spatial patterns in species composition and abundance
are summarized below according to survey.
5.3.3.1 Summer Survey
Four station cluster groups and nine species cluster groups were identified for the summer
survey (Figure 5.3-1). Station cluster groups for the most part consisted of a mix of outer and
inner harbor stations without a clear distinction between inner and outer harbor habitats. One
exception was the separation of outer harbor shallow-water habitats (Stations LA2, LA3, LB2,
LA7, LA8) from open-water, deepwater habitats (Stations LA1, LB1, LB9, LA11, LA12).
Outer harbor open-water habitats in deep water were characterized by relatively higher
abundances of ophiuroid echinoderms (Amphiodia urtica), amphipod (Eochelidium sp. A) and
ostracod (Euphilomedes carcarodonta) crustaceans, bulloid gastropods (Volvulella panamica),
bivalve molluscs (Nuculana taphria), and polychaete worms (Laonice cirrata, Nereis sp. A,
Streblosoma sp. B). Shallow-water outer harbor stations were characterized by relatively higher
abundances of amphipod crustaceans (Amphideutopus oculatus, Corophium heteroceratum),
California surf clam (Mactrotoma californica), and polychaete worms (Pseudopolydora
paucibranchiata, Cossura candida). Several of these outer harbor species have been
associated with background or low enrichment environments associated with open-water
coastal areas (MEC 2002).
2008 Biological Surveys of Los Angeles and Long Beach Harbors 5–5
April 2010