2011 Mugu Lagoon Benthic Infauna Report 7
MBC Applied Environmental Sciences, 3000 Red Hill Avenue, Costa Mesa, CA 92626 (714) 850-4830
Disturbance for all indices, with an overall integrated Benthic Community Index value of Moderate
Disturbance at both western arm stations.
In the main lagoon, lowest species richness and abundance were reported at Station
ML3, the easternmost station in the lagoon, while lowest biomass and diversity were found at
Station ML74 in the central lagoon. Still the communities found at Stations ML3 and ML74 were
as similar to each other as were the two stations in the western arm. In 2008, the results of the
community indices were mixed between Low and High Disturbance at Station ML3 resulting in an
overall rank of Moderately Disturbed (MBC 2009). In 2011, however, only the BRI indicated
Moderate Disturbance while three indices and the overall integrated Benthic Community Index
value indicated that the community at Station ML3 was Highly Disturbed. In 2011, Station ML74
was the only station to show improvement from the 2008 results. The station is influenced by
inputs from both the creek and a nearby storm drain. In 2008 community indices ranged from
Moderate to High Disturbance, with an overall integrated rank of High Disturbance, while in 2011
indices were highly variable, ranging from reference condition for the BRI to High Disturbance for
the RBI, with an overall integrated Benthic Community Index of Moderate Disturbance. Also in the
eastern arm of the lagoon, Station ML15 is the closest to Calleguas Creek. While species
richness was the second lowest here in 2011, abundance was the second highest. In 2008,
community indices suggested Low to Moderate Disturbance at Station ML15, with an overall
integrated level of Moderate Disturbance. In 2011, though, only the IBI indicated Moderate
Disturbance while three indices and the overall integrated Benthic Community Index value
indicated that the community at Station ML15 was Highly Disturbed.
Changes in the infaunal communities such as those noted this year are not unusual in
lagoon habitats. Coastal lagoons are subject to a variety of influences on daily, seasonal and
annual timescales. These influences include changes in water level, salinity and temperature as a
result of tides, seasonal runoff during winter rainstorms and periodic unusually large storms or
very wet years. While all of these influence the communities, large-scale events can have
considerable impacts on the infaunal community. These impacts could include changes in
sediment characteristics such as deposition of new sediments or scouring of existing sediments,
dramatic short-term changes in salinity, or physical removal of individuals in stormwater flow. All
of these can result in the reduction of individuals and alteration or elimination of existing
communities. Timing of sampling following a dramatic reduction in the previous community is
important because species that are more likely to be among the first to re-colonize an area are
also generally among species known to be tolerant of ongoing disturbance and pollutants. In
addition, modifications of the habitat following a large-scale event could promote re-colonization
by different species than found in the area existed prior to the storm impacts
Differences in the infaunal community between years have been observed previously at
Mugu Lagoon, with these changes chiefly associated with large-scale storm events and re-
colonization and recovery following these events (Onuf 1987). A review of rainfall in the project
area indicates that during the year previous to the 2011 sampling, rainfall in the area was the
highest in six years, and more than double the amount recorded in the year previous to the 2008
sampling (VCWPD 2011). These records, along with the previous observations of changes in the
infauna community following storms suggests that the differences noted in the community and the
resultant reduction in the community indices are likely related to the affects of an unusually wet
year previous to the 2011 survey.
CONCLUSION
In 2011, infaunal community parameters at most stations were reduced compared to
results found during the 2008 survey, with overall number of taxa reduced by 40%. Total
abundance only represented about 25% of the previous total. The Benthic Community Index
Integration indicted that the stations in the western arm of Mugu lagoon were Moderately
Disturbed in 2011 compared to the Low Disturbance found in 2008. In the main lagoon, the
benthic communities at the stations in the eastern arm indicated High Disturbance this year,
2011 Mugu Lagoon Benthic Infauna Report 8
MBC Applied Environmental Sciences, 3000 Red Hill Avenue, Costa Mesa, CA 92626 (714) 850-4830
which was also a reduction in condition compared to 2008. In the central lagoon, which is
influenced by inputs from both the creek and a nearby storm drain, indices suggested that
conditions had improved and are now considered Moderately Disturbed compared to the High
Disturbance previously found. While higher levels of disturbance to the infauna community were
indicated in 2011 than in 2008, the source of the disturbance is likely related to the affects of an
unusually wet year previous to the 2011 survey.
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