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

6.0 Riprap Biota
6.6 SUMMARY OF SPATIAL AND TEMPORAL VARIATIONS
Tide level influences the development of the riprap community in the harbors. Riprap biota was
less diverse and abundant in the upper intertidal compared to lower intertidal and subtidal depth
zones. However, biomass was relatively similar across depth. Dominant animals of the upper
intertidal (e.g., barnacles, limpets) have shells that protect them from desiccation during low
tides, which also contributes to the relatively high biomass for the upper intertidal zone. Fewer
differences in number of species and abundance were apparent between lower intertidal and
subtidal depths.
Generally, the riprap community was similar among inner and outer harbor areas. The only
notable difference was a relatively greater number of species and abundance at breakwater
habitats in the outer harbor (Stations LARR1, LBRR2) and at a piling habitat surveyed in the
inner harbor (Station LARR3).
Dominant species generally were similar throughout the harbors. However, some differences
were noted that may have been associated with attachment substrate. For example, the piling
habitat surveyed at Station LARR3 supported greater numbers of mussels, dwarf brittlestars,
and tunicates than other stations located on rock riprap or boulders.
6.7 HISTORICAL COMPARISONS
Results of the present study were similar to previous studies, which have found tide level to be
the major factor associated with the distribution of riprap organisms (MBC 1984, MEC 1988,
2000). Similar to historical studies, barnacles dominated the upper intertidal and a greater
variety of organisms were present in the lower intertidal and subtidal zones. The Mediterranean
mussel Mytilus galloprovincialis was conspicuous in the lower intertidal and shallow subtidal.
Previous studies have noted increased community development with depth. The present study
also documented lower community development in the upper intertidal, but noted similar
community development at both lower intertidal and subtidal depths. As pointed out in the 2000
study (MEC 2002), variations in where samples are collected along the tide gradient and slight
sampling differences likely contribute to reported differences in community development with
depth.
Historical studies also have noted relatively greater community development in outer harbor
compared to inner harbor areas (MEC 1988, MEC 2002). A notable finding of the present study
was the overall similarity in community development throughout the harbors. Although diversity
was somewhat greater at outer harbor breakwater stations (LARR1, LBRR1), the difference was
mainly associated with the upper intertidal zone. Community summary measures did not show
distinct trends among inner and outer harbor stations for the lower intertidal and subtidal zones.
Somewhat different species assemblages were observed at some stations that may have been
related to substrate or site-specific environmental conditions; however, no large-scale
differences in riprap community development were noted between inner and outer harbor areas.
This result suggests a relative improvement in environmental quality at inner harbor stations
since the 2000 study.
6.8 EXOTIC SPECIES
A total of 12 non-indigenous (introduced) species was collected, representing approximately 3%
of the 334 observed species in the riprap community (Appendix F). Another 31 species were
cryptogenic (of unknown origin). Thus, approximately 13% of the riprap fauna were potentially
non-native in origin. The species were associated with a variety of taxonomic groups, including
ascidians, amphipod crustaceans, ophiuroid echinoderms, molluscs, nemerteans, and
2008 Biological Surveys of Los Angeles and Long Beach Harbors 6–7
April 2010