INTRODUCTION:
Andaman and Nicobar Islands comprises of 572 islands in 900km long
from Landfall Island in the north to Great Nicobar Island at the south are
representing a variety of faunal communities. Scleractinian
corals are the most important life form of the shallow water environment of
tropical sea including A and N Islands. Among the known 25 families (Venkataraman and Satyanarayana,
2012) of scleractinian, Acroporids
are the most important representatives with the maximum number of 277
individuals belong to 4 gerera, of which 182 species
belong to Acropora, 7 species belong to Anacropora, 13 species belong to Astreopora and 75 species belong to Montipora (Veron,
2000). Acroporidae, the reef building corals, are
very important due to their reef assemblage in the Indo-Pacific Oceans. The
species under the genus Acropora is found in quite diversified form and
popular in respect to their growth forms like branching, cluster, busy,
finger-like etc. Species of this family is also known as small polyp scleractinian. Anacropora is the
genus with slow growth rate and it is closely similar to Montipora. Astreopora species are mound shaped or
encrusting. Montipora
represents second maximum number of species followed by Acropora. The species under Montipora can be
seen as branching, foliaceous, laminar, encrusting,
and fingered with “fuzzy” polyps.
In 2003, Venkataraman
et al. described 70 species of acroporids
under 3 gerera which include 20 species of genus Montipora, 47 species of genus Acropora and 3 species of genus Astreopora corals
from India where as 70 species of acroporids 54
species belong to 3 genera such as 10 species of genus Montipora, 42 species of genus Acropora and 2
species of genus Astreopora
were reported from Andaman and Nicobar Islands.
In 2012, Venkataraman and Satyanarayana
described key characters for 99 species of acroporids
belong to 3 above said genera such as 26 species under Montipora, 67species under Acropora and 6
species belong to Astreopora.
The present study describes diversity and distribution of a total 158 species
of acroporids under four genera viz
Genus Acropora
with 105 species, Anacopora with 2 species, Astreopora with 8 species and Montipora with 43
species from Andaman and Nicobar Islands.
MATERIAL AND
METHODS:
A total of 290 sites of Andaman and
Nicobar Islands were studied during underwater surveys by employing Self-Contained
Underwater Breathing Apparatus (SCUBA) diving, snorkeling during the period of
July, 2009 to January, 2013 to record the species of scleractinian
corals. A series of 20 m
transects were placed at random sampling method to continue Line Intercept Transect
Method (Bradbury et al., 1986) along
with the Quadrate methods (Endean and Stablum, 1973)
to explore the diversity of the scleractinian corals
of the surveyed areas. Photography of quadrates was made with a housed digital
camera (Sony - Cyber shot, Model-T900, marine pack, 12.1 megapixels and Sony -
Cyber shot, Model-TX1, marine pack, 10.2 megapixels).
Identification of species was made in conjunction with Veron
and Wallace (1984) and Veron (2000).
The species
diversity of corals was evaluated following Shannon-Weaver diversity index
formula as described below (Shannon, 1948)
H'= -∑pi ln 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.
Simpson’s
diversity index (Simpson, 1949) 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 (Pielou,
1966)
J’=H'/H'max
Where H' is the number derived from the
Shannon diversity.
RESULTS:
A total of 158 species (Table-1) of scleractinians
were reported from the entire Andaman and Nicobar Islands during the study
periods. Species under all the four genera were reported during the scleractinian exploration. The entire study areas were
divided in three regions to make a comprehensive report on their diversity,
distribution and evenness. All the four genera were reported only from South
Andaman whereas other two represent the three among those except Anacropora. The
genus Acropora represents the maximum number of 105
species among the total report of 158 species while Anacropora represents only 2 species exclusively from South Andaman. North
and Middle Andamans represent the maximum number of
92 species under Acropora whereas South Andaman represents the
maximum number of 36 species under Montipora. Species
belonging to Astreopora were reported same in number (7
species) from both the areas such as North and Middle Andaman and South
Andaman. Nicobar region represent the minimum number of species under the three
genera such as Acropora,
Astreopora
and Montipora. A maximum number of 136 species were
reported from South Andaman while the minimum of 52 were from Nicobar (Table
1). All the analyzed indices such as Shannon-Weaver diversity index, Simpson’s
density index and Pielou’s evenness index were
maximum (5.82, 0.98 and 0.94) at South Andaman while minimum (4.5, 0.91 and
0.91) was encounter at Nicobar (Fig. 1).