MBC Applied Environmental Sciences, 3000 Red Hill Avenue, Costa Mesa, CA 92626 (714) 850-4830
CALLEGUAS CREEK WATERSHED MONITORING PROGRAM
2011 MUGU LAGOON BENTHIC INFAUNA REPORT
INTRODUCTION
The benthic infauna, invertebrates that live in the bottom sediments, are an important part
of the marine ecosystem. These animals are a major food source for fish and other larger
invertebrates, and contribute to nutrient recycling. Some species are highly sensitive to effects of
human activities, while others thrive under altered conditions. The assessment of the benthic
community is, therefore, a major component of many marine monitoring programs.
As part of the Calleguas Creek watershed
Total Maximum Daily Load (TMDL) monitoring
program, the benthic infaunal community of Mugu
Lagoon, an estuarine embayment at the mouth of
the creek, was sampled (Figure 1). Benthic
sampling was included in the monitoring program to
assess infaunal community condition, a potential
indicator of exposure to contaminants in the
sediments. Infaunal community composition, in
conjunction with toxicity testing and chemical
analysis, form a triad of standardized tools to
determine sediment quality in potentially impacted
habitats and provide managers and regulators a
means to assess and evaluate local conditions in
comparison to regional Sediment Quality Objective
(SQO) criteria.
MATERIALS AND METHODS
Benthic samples for the analysis of infauna
community were collected in conjunction with
sediment monitoring on 16 through 18 August 2011
at five stations within Mugu Lagoon (Figure 1, Table
1). A single grab for infauna analysis was collected
at each station using a chain-rigged, 0.1 square
meter (m
2
) van Veen grab. Each sample was
washed in the field using a 1.0-mm U.S. Standard
Sieve, labeled, relaxed in an isotonic solution of
magnesium sulfate for a minimum of thirty minutes
and fixed in buffered 10% formalin-seawater.
In the laboratory, samples were transferred to 70% ethyl alcohol, sorted to major
taxonomic groups, identified to the lowest practical taxonomic level, and counted. Identifications
and nomenclature followed the 2011 usage accepted by the Southern California Association of
Marine Invertebrate Taxonomists (SCAMIT 2011). Representative specimens were added to
MBC's reference collection. Following identification, the weight of organisms for each major
taxonomic group was measured. Specimens were placed on small, pre-weighed mesh screens
that had been immersed in 70% ethyl alcohol, blotted on a paper towel, and air-dried for five
minutes. Large organisms, if any, were weighed separately.
Figure 1. Mugu Lagoon infauna sampling
stations.
2011 Mugu Lagoon Benthic Infauna Report 2
MBC Applied Environmental Sciences, 3000 Red Hill Avenue, Costa Mesa, CA 92626 (714) 850-4830
Following identification and enumeration of infaunal species, counts tabulated by taxonomists on
laboratory bench sheets were entered into MBC’s in
-house, Microsoft Access-based infauna
database. All information was double entered for accuracy and species names were compared
with both the in-house database and the
current SCAMIT nomenclature list to validate
usage. Data were compared among stations
using
both
summary
information
and
mathematical analysis. Analytical methods
included: Shannon-Wiener species diversity
(H'); comparison of community composition
among stations using Euclidean distance; and
four indices of benthic community condition
(Southern California Benthic Response Index
[BRI], Index of Biotic Integrity [IBI], Relative
Benthic Index [RBI], and River Invertebrate
Prediction
and
Classification
System
[RIVPACS]). Since these four indices use
different species constituents and methods to
evaluate community conditions (BRI and IBI
are based on community measures, while
RBI and RIVPACS on species composition)
relative impact levels may differ between
methods. To account for these differences
and provide a comprehensive evaluation of
condition, the median of the four index
category scores for each station was used to
determine the Benthic Community Index
Integration score, which is used in the SQO
evaluation. Descriptions of methods are
presented in Appendix A.
RESULTS
Species Composition. A total of
2,754 individuals in 49 species (or taxa) and
ten phyla (major groups) were taken in the
benthic infauna sampling at Mugu Lagoon
(Figure 2, Table 2 and Appendix B). Annelids
(segmented worms) were the most diverse
phylum, with 21 species (43% of the total),
followed by arthropods with 14 species
(29%), mollusks with nine species (18%), and
nemertean (ribbon) worms with three species
(6%). The remaining two phyla, nematodes
Table1. Mugu Lagoon station coordinates, date and time of sampling and water depth.
Infauna
Station ID
Station
Reference
Number
Actual
North
Latitude
Actual
West
Longitude
Sample Date
Sample
Time
(hr)
Depth (m)
at Time of
Collection
ML3
01 BPT 3
34° 06.139'
119° 05.464'
17 August 2011
1315
1.4
ML6
01 BPT 6
34° 06.158'
119° 06.571'
18 August 2011
1050
1.4
ML14
01 BPT 14
34° 06.279'
119° 07.030'
18 August 2011
930
1.0
ML15
01 BPT 15
34° 06.333'
119° 05.626'
17 August 2011
1030
1.4
ML74
01 SG 74
34° 06.044'
119° 05.769'
16 August 2011
1430
0.6
station.