Southern California Benthic Response Index (BRI)
The Southern California Benthic Response Index (BRI) is an abundance-weighted
average pollution tolerance of species occurring in a sample, and is a measure of the condition of
marine and estuarine benthic communities (Smith et al. 2003). It classifies benthic communities
as undisturbed (reference) or one of four levels of response to increased disturbance: Level 1,
marginal deviation, or minimal disturbance; Level 2, biodiversity loss, in which more than 25% of
species typical of undisturbed sites are not present; Level 3, community function loss, more than
90% of echinoderm and 75% of arthropod species at undisturbed sites are not present; and Level
4, defaunation, more than 90% of species found at undisturbed sites are not present. The formula
is:
Benthic Response:
BRI
s
=
where: BRI
s
= BRI value for sampling unit s
i
n
= number of species with pollution tolerance scores in s
i
p
i
= pollution tolerance of species i
a
si
= abundance of species i in s
Species pollution tolerances p
i
were determined during BRI development as the position
of the abundance distribution of species i on a gradient between the most and least disturbed
sites. Species without pollution tolerance values are not included in the calculation. Pollution
tolerance values were not assigned to species if the data were insufficient to assign a value. The
index was developed for benthic samples that were sieved through a 1-mm mesh screen.
Pollution tolerance scores were derived for coastal shelf samples for shallow (10-30 m deep),
mid-depth (>30-120 m deep), and deep (>120-324 m deep) habitats, and for bay and harbor
habitat samples, northern (Point Conception to Newport Bay) and southern (Dana Point to the
U.S.-Mexico border). The species names for which scores are available are based on Edition 6 of
the Southern California Association of Marine Invertebrate Taxonomists (SCAMIT) list of
invertebrate species (SCAMIT 2011).
The BRI score is compared to the BRI thresholds.
Index of Biotic Integrity (IBI)
To calculate IBI the total number of taxa, number of mollusk taxa, abundance of
Notomastus sp., and the number of sensitive species is needed. The sensitive species list should
be from the list for the station’s habitat. There are three steps needed to determine the IBI
category and score (SCCWRP 2008).
Table 1. BRI Category Thresholds
BRI Score
Category
Category Score
< 39.96
Reference
1
> 39.96 to < 49.15 Low Disturbance
2
> 49.15 to < 73.27 Moderate Disturbance 3
> 73.27
High Disturbance
4
a p
a
si
i
i
n
si
i
n
4
1
4
1
=
=
∑
∑
Step one: calculate the percentage of sensitive taxa present.
Percent (%) sensitive taxa = (number of sensitive taxa/total number of taxa) X 100
Step two: compare the values from step one to the reference ranges for IBI (Table 2).
When the value falls out of these ranges the IBI score is increased by one (with a starting value of
zero).
Step three: compare the IBI score determined in step two with the IBI category
thresholds (Table 3).
Relative Benthic Index (RBI)
The RBI is the weighted sum of: (a) four community metrics related to biodiversity (total
number of taxa, number of crustacean taxa, abundance of crustacean individuals, and number of
mollusk taxa), (b) abundances of three positive indicator taxa, and (c) the presence of two
negative indicator species (SCCWRP 2008). The positive indicator species are: Monocorophium
insidiosum, Asthenothaerus diegensis, and Goniada littorea. The negative indicator species are
Capitella capitata complex and Oligochaeta.
Step one: normalize the values for the benthic community metrics. Use the formulas
below for the scaled values.
Total number of taxa / 99
Number of mollusk taxa / 28
Number of crustacean taxa / 29
Abundance of crustaceans / 1693
Step two: use the scaled values to calculate the Taxa Richness Weighted Value (TWV).
TWV = Scaled total number of taxa + Scaled number of mollusk taxa + Scaled number of
crustacean taxa + (0.25 X Scaled abundance of Crustacea)
Step three: calculate the negative indicator taxa (NIT) value. The NIT starts at a zero
value. If Capitella capitata complex and / or Oligochaeta are present in any amount the NIT
decreases by 0.1. If neither were found the NIT = 0, if both are found the NIT = -0.2.
Step four: calculate the value for the positive indicator taxa (PIT). Use the following
formulas to calculate the PIT value for each species:
Table 2. Reference Ranges for IBI
Metric Reference
Range
Total Number of Taxa
13 to 99
Number of Mollusk Taxa
2 to 25
Abundance of Notomastus sp 0 to 59
Percentage of Sensitive Taxa 19 to 47.1
Table 3. IBI Category Thresholds
IBI Score Category
Category Score
0 Reference
1
1 Low
Disturbance
2
2 Moderate
Disturbance 3
3 or 4
High Disturbance
4
4
4
Monocorophium insidiosum abundance
473
4
4
Asthenothaerus deigensis abundance
27
4
4
Goniada littorea abundance
15
The individual species PIT values are summed to calculate the PIT sample value. If none
of the three species are present, then the sample PIT = 0.
Step five: calculate the raw RBI:
Raw RBI = TWV + NIT + (2 X PIT)
Step six: calculate the RBI Score, normalizing the Raw RBI by the minimum and
maximum Raw RBI values in the index development data:
RBI Score = (Raw RBI - 0.03)/4.69
The final step is to compare the RBI Score to the RBI thresholds, determining the RBI
category.
River Invertebrate Prediction and Classification System (RIVPACS)
The RIVPACS index calculates the number of reference taxa present in the test sample
(observed or “O”) and compares it to the number expected to be present (“E”) in a reference
sample from the same habitat (SCCWRP 2008).
Step one: Determine the probability of the test sample belonging to twelve Southern
California Marine Bays reference sample groups. The sampling bottom depth, latitude, and
longitude are needed for this step.
Step two: determine the identity and expected number of reference species for each
sample, based on the probabilities of group membership calculated in Step 1 and the distribution
of reference species in each group.
Steps one and two use a computer program to calculate the values. The calculations can
be made at the Utah State University Western Center of Monitoring and Assessment of
Freshwater Ecosystems website (USU 2009). To use this site data must be put into a format that
Table 4. RBI Category Thresholds
RBI Score
Category
Category Score
> 0.27
Reference
1
> 0.16 to < 0.27 Low Disturbance
2
> 0.08 to < 0.16 Moderate Disturbance 3
< 0.08
High Disturbance
4
the program recognizes. There are five files necessary to run the program. Two files, one with
habitat data and the second file with macrofauna data are prepared by the user. Three files are
provided that contain relevant southern California information on the reference sample group
means, inverse covariance matrix, and macrofauna data (SCCWRP 2008). The data are entered
into the Utah State University site and the RIVPACS scores determined are compared to the
threshold categories and be given a Category Score.
Table 5. RIVPACS Category Thresholds
RIVPACS Score
Category Category
Score
> 90 to <1.10
Reference
1
> 0.74 to < 0.90
or
Low Disturbance
2
> 1.10 to < 1.26
>0.32 to < 0.74
or
Moderate Disturbance 3
> 1.26
< 0.32
High Disturbance
4
Integrate Benthic Index Category Scores
The four benthic index category scores were combined to create a single benthic index.
The integrated scores were calculated by taking the median of the four individual index category
scores. If the median falls between two categories the value is rounded up.
Table 6. Index Category Score
Category Category
Score
Reference 1
Low Disturbance
2
Moderate Disturbance 3
High Disturbance
4
Appendix B
Survey Results
Appendix B-1. Infaunal master species list. Mugu Lagoon, 2011.
Appendix B-2. Infauna results by station. Mugu Lagoon, 2011.
Station
Percent
Phylum
Species
ML3
ML6
ML14
ML15
ML74
Total
Total
NT
Nematoda
11
632
26
42
6
717
26.03
AR
Oxyurostylis pacifica
-
178
300
-
3
481
17.47
AR
Monocorophium acherusicum
-
2
-
306
-
308
11.18
AN
Oligochaeta
-
159
108
15
20
302
10.97
AR
Grandidierella japonica
4
-
-
282
-
286
10.38
AR
Harpacticoida
-
-
-
-
176
176
6.39
AN
Notomastus tenuis
6
97
-
-
3
106
3.85
MO
Acteocina inculta
-
20
26
-
-
46
1.67
AR
Monocorophium uenoi
-
-
1
36
8
45
1.63
AN
Capitella capitata Cmplx
1
-
-
34
1
36
1.31
AR
Allorchestes angusta
-
17
-
2
15
34
1.23
AN
Hemipodia borealis
16
-
-
-
14
30
1.09
AN
Mediomastus ambiseta
-
23
1
-
-
24
0.87
MO
Macoma nasuta
-
22
1
-
-
23
0.84
AN
Streblospio benedicti
-
16
1
3
-
20
0.73
NE
Lineidae
-
13
1
-
-
14
0.51
AN
Mediomastus californiensis
-
11
1
-
-
12
0.44
AR
Cyprideis miguelensis
-
-
-
-
12
12
0.44
AN
Armandia brevis
-
-
-
-
10
10
0.36
AN
Pseudopolydora paucibranchiata
-
1
-
-
9
10
0.36
AN
Glycinde polygnatha
-
6
2
-
1
9
0.33
AN
Paranoides platybranchia
-
-
-
5
-
5
0.18
NE
Paranemertes californica
-
1
2
1
1
5
0.18
MO
Macoma secta
1
-
2
-
1
4
0.15
AN
Prionospio (Minuspio) lighti
-
3
-
-
-
3
0.11
AN
Spiophanes duplex
-
1
2
-
-
3
0.11
AR
Neotrypaea sp
-
-
1
-
2
3
0.11
MO
Tagelus sp
-
1
2
-
-
3
0.11
AN
Polydora cornuta
-
-
-
2
-
2
0.07
AN
Spiochaetopterus costarum Cmplx
-
-
-
-
2
2
0.07
AR
Monocorophium sp
-
-
2
-
-
2
0.07
MO
Cumingia californica
2
-
-
-
-
2
0.07
MO
Rochefortia tumida
-
-
2
-
-
2
0.07
MO
Tryonia imitator
-
2
-
-
-
2
0.07
AN
Ctenodrillus serratus
-
1
-
-
-
1
0.04
AN
Glycera macrobranchia
-
-
-
1
-
1
0.04
AN
Ophiodromus pugettensis
-
-
1
-
-
1
0.04
AN
Pectinaria californiensis
-
1
-
-
-
1
0.04
AN
Platynereis bicanaliculata
-
-
-
-
1
1
0.04
AN
Polyophthalmus pictus
-
-
-
-
1
1
0.04
AR
Cyprideis stewarti
-
-
-
-
1
1
0.04
AR
Dolichopodidae (pupa)
-
1
-
-
-
1
0.04
AR
Excirolana chiltoni
-
-
-
1
-
1
0.04
AR
Haplocytheridea maia
-
-
-
-
1
1
0.04
AR
Podocopida
-
-
-
-
1
1
0.04
MO
Haminoea vesicula
-
-
-
1
-
1
0.04
MO
Leukoma staminea
-
1
-
-
-
1
0.04
NE
Hoplonemertea
-
-
-
-
1
1
0.04
PR
Phoronopsis sp
1
-
-
-
-
1
0.04
Number of individuals
42
1209
482
731
290
2754
Number of species
8
23
19
14
23
49
Diversity (H')
1.63
1.62
1.21
1.39
1.68
2.36
Appendix B-3. Infaunal wet weight biomass data (g). Mugu Lagoon, 2011.
Station
ML3
ML6
ML14
ML15
ML74
Total
Annelida
0.9249
3.4849
0.1852
0.2731
0.9355
5.8036
Arthropoda
0.0150
0.3301
0.3795
0.9666
0.0742
1.7654
Mollusca
<0.0001
13.4826*
0.790
<0.0001
<0.0001
0.7904
Misc.
0.0789
0.1132
0.0076
<0.0001
<0.0001
0.1997
Total
1.0188
3.9282
1.3627
1.2397
1.0097
8.5591
Note: - = no animals
* 2 large Macoma nasuta weighing 8.1601 g
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