2011 Mugu Lagoon Benthic Infauna Report 5
MBC Applied Environmental Sciences, 3000 Red Hill Avenue, Costa Mesa, CA 92626 (714) 850-4830
Table 3. The 12 most abundant species by station.
Cluster Analyses. The 12 most abundant species were used for the normal (site-group)
and inverse (species-group) cluster analyses (Figure 3).
Cluster diagrams were drawn based on
dissimilarities with a value of 1.5 determined
a priori as the minimal value indicating a significant
separation between faunal and station groups. Stations ML3 and ML74 (Group I) and Stations
ML6 and ML14 (Group III) clustered together at similar levels based on the similarity of
communities between the two stations in each group. Station ML15 (Group II), nearest Calleguas
Creek, clustered more closely to the Group I stations in the eastern arm than to the western arm
stations. Group I stations clustered together based a similar contribution by species comprising
Group A, along with low abundances of many of the common species. Group III was clustered
based on species in Groups D and E, while Group II was influenced by the high abundances of
Group C species that occurred in low to moderate abundances, if at all, at the other stations.
ML3 ML74 ML15 ML6 ML14
II
Hemipodia borealis
Notomastus tenuis
Allorchestes angusta
Harpacticoida
Capitella capitata Cmplx
Monocorophium uenoi
Grandidierella japonica
Monocorophium acherusicum
Acteocina inculta
Oxyurostylis pacifica
Oligochaeta
Nematoda
2.50
0
.0
2
.0
D
is
s
im
ila
rit
y
0.0
Key:
Percent Species Mean
= 0-74
= 75-125
= >125
Dissimilarity
A
III
I
B
C
D
E
Figure 3. Two-way coincidence table resulting from normal (station) and inverse (species)
classification dendrograms for the top one percent of infaunal species.
2011 Mugu Lagoon Benthic Infauna Report 6
MBC Applied Environmental Sciences, 3000 Red Hill Avenue, Costa Mesa, CA 92626 (714) 850-4830
The most abundant species clustered into five groups based on their occurrences
(Figure 3). Group A included the annelids Hemipodia borealis, which was found only at Group I
stations and Notomastus tenuis, which was found in similar abundances at the Group I stations
but was most abundant at Station ML6 in Group III. Group B taxa included the amphipod
Allorchestes augusta and hapacticoid copepods, both of which occurred frequently at Station
ML74 in Group I. Group C was composed of four species, an annelid and three amphipods that
were most abundant at Station ML15 (Group II). Group D included the gastropod Acteocina
inculta and the amphipod Oxyurostylis pacifica, which were taken almost exclusively at Group II
stations. Group D was formed by oligochaets and nematodes, the two most frequently observed
taxa during the survey, although both were most abundant at Group III stations.
DISCUSSION
The infauna communities in the study area in 2011 were composed predominantly of
nematodes, small arthropods, annelid worms and gastropods. Community composition was most
similar between Stations ML6 and ML14 in the western arm of the lagoon, and between Stations
ML3 and ML74 in eastern arm and the central lagoon, respectively. Greatest number of taxa was
reported at both Stations ML6 and ML74, although abundance at Station ML6 was about 60%
higher than found at the station with the second highest abundance. Biomass was also greatest
at Station ML6 where a few large individual mollusks contributed to a biomass that was nearly 13
times greater than was found at any other station. While number of taxa and individuals were
lowest at Station ML3, diversity was lowest at Stations ML14 and ML15, the stations farthest west
and north, respectively, from the central lagoon.
Compared to 2008, number of taxa reported at the five stations in the lagoon declined by
about 40% in 2011 (MBC 2009). The greatest declines were observed at Stations ML6 and ML14
in the western arm of Mugu Lagoon where the number of taxa in 2011 was less than one-half
those reported in 2008. The number of taxa also declined slightly at the western arm stations;
however, in the central lagoon, number of taxa at Station ML74 more than tripled compared to
2008. Still, seven of the most abundant taxa reported in 2008 were among the community
dominants again this year, including the same top three species. Similar to number of taxa,
overall abundance in 2011 was notably lower than reported previously, with only slightly more
than one-quarter of the 2008 abundance. The greatest difference was found at Station ML14
where less than 10% of the individuals reported in 2008 were taken this year. Abundance was
reduced by about one-half at all of the remaining stations except for Station ML74, where, like
taxa, number of individuals was higher than reported in 2008. Biomass in 2011 was similar to that
found in 2008, with mollusks accounting for most of weight during both surveys, although in the
previous survey larger individuals were found at both stations in the western arm of the lagoon.
As a result of these differences between years, diversity was lower at all stations except Station
ML74 in 2011, although the overall diversity for all stations combined was the same during both
surveys.
Within Mugu Lagoon the western arm is separated from the rest of the lagoon by a
causeway with culverts that mute tidal exchange and likely reduce exposure to contaminants
washed downstream from Calleguas Creek. Though the western arm may be subject to inputs
from the military base and nearby airfield, in general the western arm is buffered from surface
runoff by marsh. In 2008, all community parameters, including species richness, abundance,
diversity and biomass were highest at the western arm stations, with highest abundance and
biomass values reported at Station ML14 farthest from the causeway (MBC 2009). In 2011, these
community parameters were reduced at the stations in the western arm, particularly at Station
ML14. In 2008, the infauna communities of the western arm stations indicated the least
disturbance of the stations sampled in the lagoon, with all indices suggesting Reference or Low
Disturbance levels at both stations and an overall integrated Benthic Community Index value of
Low Disturbance for both western arm stations. In 2011, the stations in the western arm were still
among the least disturbed in the lagoon, however, at levels indicating Low-to-Moderate