The species
diversity of corals was evaluated following Shannon-Weaver diversity index
formula as described below [7].
H’= -∑pi loge pi
Where, pi =
Proportion of number of individual of a particular species and total number of
individual of all the species, H’= diversity of a theoretically infinite
population.
Similarity Index is the simple measure of the extent to
which two habitats species in common. The Sørensen index, also known as Sørensen’s similarity coefficient, is a statistic used
for comparing the similarity of two samples [8].
It has been formulated below
QS=
(2C/A + B)
Where, A and B are
the species numbers in station A and B, respectively, and C is
the number of species shared by the two stations. This expression is easily
extended to abundance instead of incidence of species.
Simpson’s
diversity index [9] is one of the truthful indices to calculate the species
diversity of any study site. It has been applied to calculate the species
diversity of scleractinian corals of those islands.
The formula for the Simpson index is:
D=1-
Where S is the number of species, N is
the total percentage cover or total number of organisms and n is the
percentage cover of a species or number of organisms of a species. In this
form, D ranges from 1 to 0, with 1 representing infinite diversity and 0
representing no diversity.
Evenness of a community was described by the Pielou’s Evenness Index (J’). The formula of the index is [10]-
J’=H’/H’max
Where H' is the number derived from the Shannon diversity.
RESULTS:
A total 88 species of faviids
were recorded under 18 genera from the study areas. The genus Favia shown a maximum of 18 species followed
by Favites where it was 13 species. However the
genus Diploria, Colpophyllia, Plesiastrea, Oulastrea, Diploastrea and Solenastrea represented
with single species only. Among them, South Andaman region showed maximum
number of species composition (85 species) with Shannon-Weaver diversity Index
(H’= 5.96), Simpson Density Index (D= 0.98) and Pielou’s
Evenness Index (J= 0.93) in comparison with the other two regions of these
group of islands (Fig-1). The minimum was recorded at Nicobar region with 49
species of faviids and the species diversity, density
and evenness indices are 5.13, 0.96 and 0.92 respectively (Table-1). The
similarity of the species composition shows a significant amount of a maximum
0.95 in between North and Middle Andaman and South Andaman regions (Table-2).
Table-2
Sorensen’s similarity index
|
|
South
Andaman |
Nicobar |
|
North
and Middle Andaman |
0.95 |
0.68 |
|
Nicobar |
0.68 |
|
Fig-1- Comparative study on Species Diversity (H’), Density (D) and
Evenness (J)
DISCUSSION:
Scleractinian corals are denoted as
marine rainforest due to its productivity towards the marine biodiversity from
the primary level to tertiary. Due course of time with the exponential efforts
of the several expeditions as well as surveys, it was revealed out that scleractinians are widely distributed with varied species
composition mostly in tropical regions of the world nevertheless species of the
same were also recorded from other parts. Record of 126 species of faviids under 24 genera was made by Veron
[1] in global scenario. In 2003, Venkataraman et al. made a record to describe 36
species of faviids under 13 genera [11]. Ramakrishna et
al. (2010) also recorded a checklist of 78 species of faviids
under 16 genera from Andaman and Nicobar Islands [12]. The gradual increment on
the exploration of species in this group of islands depicts the progressiveness
in bio-diversity nodules of these areas. With that extensive effort, present
study revealed out 88 species under 18 genera. Finding out of 85 species with
Shannon-Weaver diversity Index (H’= 5.96), Simpson Density Index (D= 0.98) and Pielou’s Evenness Index (J= 0.93) is itself a self
introductory phenomenon of that place to say about the biogenic habitat of that
area. Though the H’, J and D values of other two areas are lesser than the
above one, but it can be said that, the species composition, diversity,
distribution and evenness of North and Middle Andaman are very closer to South
Andaman as it showed 0.95 similarity index. Nicobar region of the study area is
relatively less diverse in species with the other two areas with Shannon-Weaver
diversity Index (H’= 5.13), Simpson Density Index (D= 0.96) and Pielou’s Evenness Index (J= 0.92), but status of the
species is good enough to mean the suitable biogenic environment of that area,
which support their recruitment, growth, biological process towards the
successive implementation of enriched species compatibility with the
surrounding environment.
ACKNOWLEDGEMENT:
Authors are grateful to the Ministry of Environment and Forests, Govt.
of India for providing financial assistance to undertake the study through the
projects of National Coral Reef Research Institute, Zoological Survey of India,
Port Blair.
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