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APPENDIX 3.

Technical Notes

The following was taken from the Institute For Environmental Modeling At University Of Tennessee, Knoxville

(www.tiem.utk.edu/~gross/bioed/bealsmodules/shannonDI.html):

The Shannon diversity index (H) is commonly used to characterize species diversity

in a community. Shannon's index accounts for both abundance and evenness of the

species present. The proportion of species i relative to the total number of species (pi)

is calculated, and then multiplied by the natural logarithm of this proportion (lnpi). The

resulting product is summed across species, and multiplied by -1:

S

H = - ∑ pi lnpi

i=1

Shannon's equitability (EH) can be calculated by dividing H by Hmax (here Hmax = lnS).

Equitability assumes a value between 0 and 1 with 1 being complete evenness.

EH = H/ Hmax = H/ lnS

Variables

Shannon's diversity index

H

total number of species in the community (richness)

S

proportion of S made up of the ith species

pi

equitability (evenness)

EH

S2 FISH DIVERSITY

Two measures that approximate diversity and abundance are REEF's Density Index and Sighting Frequency.

The following text is from REEF's website on interpreting REEF data (www.reef.org/data/interpret.htm).

The REEF Density Index (DEN) is a measure of how many individuals of a species are observed

based on a scale ranging from 1 to 4. Abundance category weights are Single = 1; Few = 2;

Many = 3; and Abundant = 4. This weighted density average (Den) is calculated as follows:

(S * 1) + (F * 2) + (M * 3) + (A * 4)

DEN =

-------------------------------------------------

(# of surveys in which species was observed)

The DEN indicates which abundance category the species was most often recorded in when

it was recorded. For example, Den=2.2 would be reflective of a species that was most often

recorded in category 2 (Few) but because the density index is greater than 2, there were some

abundances recorded for this species in the other, larger abundance categories (either category

3 or 4). The DEN index should be used as an abundance guide because area is not rigorously

controlled in the RDT method. It should also be kept in mind that the DEN parameter is reflective

of sighting distributions in the four different abundance categories (S, F, M, and A) and different

distributions of sightings in each abundance category could potentially give similar values of

DEN. In other words, it does not account for non-sightings.

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