Sediment Quality in Puget Sound Year 2 - Center for Coastal ...

Table 5. Benthic infaunal indices calculated to characterize the infaunal invertebrate
assemblages identified from each central Puget Sound monitoring station.
Infaunal index
Total Abundance
Major Taxa
Abundance
Taxa Richness
Pielou's Evenness
(J') (Pielou, 1966,
1974)
Swartz's
Dominance Index
(SDI)(Swartz et al.,
1985)
Definition
A measure of density equal to the
total number of organisms per
sample area
A measure of density equal to the
total number of organisms in each
major taxon group (Annelida,
Mollusca, Echinoderrnata,
Arthropods, miscel'laneous taxa) per
samnle area
Total number of taxa (taxa = lowest
level of identification for each
organism) per sample area
Relates the observed diversity in
benthic assemblages as a proportion
of the maximum possible diversity
for the data set (the equitability
(evenness) of the distribution of
individuals among species)
The minimum number of taxa whose
combined abundance accounts for 75
percent of the total abundance in
each samole
Calculation
Sum of all organisms counted in
each sample
Sum of all organisms counted in
each major taxon group per
sample
Sum of all taxa identified in each
sample
J' = H'llog s
Where:
s
H' = - Â pi log pi
i =I
where pi = the proportion of the
assemblage that belongs to the
it11 species (p=ni/N, where ni=the
number of individuals in the i
species and N= total number of
individuals), and where s = the
total number of species
Sum of the minimum number of
taxa whose combined abundance
accounts for 75 percent of the
total abundance in each samnle
Page 1 19