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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 3, 2012
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article ISSN 0976 – 4402
Received on October 2012 Published on November 2012 1097
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast,
India Tamilselvi. M
1, Abdul Jaffar Ali. H
2, Thilaga. R.D
3
1- Department of Zoology, V.V. Vanniaperumal College for Women,
Virudhunagar – 626 001, India
2- Department of Biotechnology, Islamiah College,
Vaniyambadi - 635 752, Tamilnadu, India
3- Department of Advanced Zoology and Biotechnology,
St.Mary’s College,Thoothukudi-626 008.
doi:10.6088/ijes.2012030133018
ABSTRACT
The present study was carried out to record the diversity, abundance and seasonal variations
of tunicates for a period of one year (from April 2000 to March 2001) from four different
stations situated along the coast of Thoothukudi, India. Totally 25 species, simple (8) and
colonial (17) ascidians, have been recorded. More number of species (19) were recorded at
station 1, followed by station 2 (11), station 3 (9) and station 4(6). The abundance of
ascidians also varied from 721/m2
(station 1) to 1252/m2
(station 4). More number of species
were recorded during premonsoon season at station 1 and less number was recorded during
summer season at station 4.Various diversity indices such as Shannon-Weiner index(H’),
Margalef’s index (d), Pielou index(J’),Taxonomic diversity index(∆), Taxonomic distinctness
index (∆+), Bray – Curtis coefficient (1957) and MDS (Multidimensional scaling) were
calculated to analyse species diversity, richness, evenness, average taxonomic distance
between two individuals, to compare the diversity between samples, similarity in species
composition and stress value respectively. The dominance plot proved the rich diversity of
ascidians at station 1 in all seasons. The dendrogram and MDS plot showed the close
similarity in species composition between the samples of Thoothukudi coast. MDS plot
illustrated an excellent ordination on the sample collected during all seasons at all stations. In
the present study, 95% confidence funnel and 95% probability contours (ellipse) showed
lower diversity of ascidians and also polluted nature of the sampling site 3.
Key words: Tunicates, Diversity, Sea squirt, Ascidiacea, Thoothukudi coast.
1. Introduction
Members of the class Ascidiacea, commonly called as tunicates or ascidians, are belonging to
the subphylum Urochordata. They are the largest and most diverse groups among the macro
fouling communities in the marine ecosystem that attach to natural and artificial substrates in
the intertidal and subtidal zones of coastal habitats throughout the world. Currently, more
than 3000 ascidian species including both simple and colonial forms, have been described in
all marine habitats from the tropics (Hernandez-Zanuy and Carballo,2001) to the poles
(Goodbody,1993, Sahade et al., 1998) and from shallow water to the deep sea (Cameron et al.,
2000 and Kott, 2005). In recent decades, marine habitats have come under increasing stress
from land based sources of pollution, shipping, physical impact of maritime activities,
dredging, coral mining etc., which in turn cause upset the number and biomass of fauna and
flora. Ascidians are one among the key ecological groups as the environmental variables
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1098
influencing their recruitment, dispersal, survival and reproduction. As ascidians provide
home for a number of aquatic fauna, a part of food chain, prey for many marine animals,
storehouse of bioactive compounds (Tamilselvi 2008; Abdul Jaffar Ali et al., 2011) and serve
as indicators to assess the quality of water (Tamilselvi et al., 2010), it is the apt time to study
their presence, distribution, seasonal variations and abundance, which are paramount
importance for the sustainable use of marine ecosystem.
Hither to, more than 400 species of ascidians have been recorded in Indian coastal waters by
various researchers at different situations (Oka, 1915; Das, 1938, 1945; Sebastian, 1952-56;
Renganathan, 1981-1984; Abdul Jaffar Ali and Sivakumar, 2007, Abdul Jaffar Ali et al.,
2009 and 2011). Thoothukudi is well known for pearl oyster ranching area which is closely
located to the Gulf of Mannar Marine Biosphere Reserve. Moreover this coast is unique by
the presence of diverse habitats such as sandy shore, sea grass, sea weed beds, rocky patches,
mud bottom etc., which provide suitable substratum for the attachment of ascidians.
Information on species diversity, richness, evenness and dominance evaluation on the
biological components of the ecosystem is essential to understand detrimental changes in
environs (Krishnamoorthy and Subramanian, 1999). Hence the present study is an attempt to
know the diversity, abundance and seasonal variation of tunicates in four stations of
Thoothukudi coast from April 2000 to March 2001.
2. Study area
Thoothukudi (80 45’N; 78
0 46’E) is an important sea Port in in the Southern peninsular India
and situated in the Gulf of Mannar area. In the present study, four stations (1,2,3, and 4) are
selected along the coastline of Thoothukudi and are shown in Figure 1. Station 1 (80 44’
53.82’’ N – Latitude, 780 12’ 15.77’’ E Longitude), is situated in Thoothukudi Port Area
having a variety of substratum like oyster beds, granite stones, coral reef, boulders,
permanent barges etc, offer a congenial rough surface for the attachment of a number of
fouling organisms. Station 2 (80 46’ 05.20’’ N – Latitude, 78
0 11’ 50.74’’ E -Longitude) is in
the outside limit of the North Break Water opposite to the cargo shed and approximately 3.2
km away from Station 1, connected to the open sea and subjected to unlimited wave action.
The calcrete stones, dead shells corals and sea weeds present in the littoral zone are excellent
habitat for the attachment of ascidians. Station 3 (80 47’ 24.25’’ N–Latitude, 78
0 9’ 35.83’’ E
Longitude) is located in between fishing harbour and Central Marine Fisheries Research
Institute (CMFRI) and approximately 10.5 km away from Station 2. This is a sandy mud area
devoid of any other substratum except plenty of sea grasses which can afford a good habitat
for a number of sedentary organisms. Fly ash from TTPS (Thoothukudi Thermal Power
Station), oil from trawlers , paints from boat yards, sewage from human dwelling place (Inico
Nagar) etc. hardly ever mix with this water and the wave action is very limited here. Station 4
(80 48’34.57’’ N–Latitude, 78
0 9’ 49.54’’ E Longitude) is situated at the backyard of the
Collector’s bungalow and approximately 3.5 km away from Station 3. Calcrete stones,
boulders and dumped granite stones present here can provide excellent habitats for the variety
of sedentary organisms. Fish landing centre (Threashpuram) is situated nearby and effluents
from textile mill and part of corporation township sewage are discharged in the vicinity of
this Station. This Station is connected with the open sea and so the influence of shore currents
is discernible here.
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1099
Figure 1: A map of the study area showing the sampling stations 1,2,3 and 4 in Thoothukudi
coast.
3. Materials and methods
Four intertidal sites (station 1, station 2, station 3 and station 4) were visited for sampling
during low tides. Samples were observed and collected monthwise from April 2000 to March
2001. A heavy rope, marked at each meter, was fixed permanently along the longest side, and
3 quadrates (1m) were randomly placed in the area by taking a distance along the rope at
random and a perpendicular distance from the rope. The mean value of quadrates were taken
and expressed as number of individuals per m2 for simple ascidians and number of colonies
per m2 for colonial ascidians. For identification, specimens of simple and colonial ascidians
were collected, photographed and transferred in a container filled with sea water. These
samples were narcotized with menthol crystals and undisturbed for an hour to two hours and
preserved in 5% formalin with sea water and identified by using Kott (1985, 1990 and 1992)
classification chart.
4. Result
A list of ascidians collected from the study area is presented in Table (1-8). Totally 25
species (simple(8) and colonial(17) ascidians ) belonging to the family Ascididae (5),
Pyuridae (2) Perophoridae (3), Styelidae (6), Holozoidae (1), Didemnidae (4), Polycitoridae
(2), and Polyclinidae (2) were recorded in four stations of Thoothukudi coast. The number of
ascidian species recorded in four stations ranged from 6 to 19. More number of species (19)
were recorded at station1, followed by station 2 (11), station 4 (9) and station 3(6).
Table 1: Seasonal variations of members of Ascididae[ individuals/m2 (mean values) ]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
1. Ascidia
sydneiensis 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0
2. A.gemmata 1 0 7 0 0 0 0 0 0 0 0 0 0 0 0 0
3. Phallusia
nigra 2 1 1 2 0 0 0 0 0 0 0 0 0 0 0 0
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1100
4. P. arabica 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0
5. P polytrema 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0
Note: Po: Post monsoon; S:Summer; Pr:Premonsoon; M:Monsoon
Table 2: Seasonal variations of members of Pyuridae [individuals/m2 (mean values)]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Herdmania pallida 9 3 1 4 0 0 0 0 0 0 0 0 0 0 0 0
Microcosmus curvus 1 5 2 1 8 7 8 9 0 0 0 0 3 1
0
1
9
1
6
Table 3: Seasonal variations of members of Perophoridae[ individuals/m2 (mean values) ]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Ecteinascidia venui 2 0 1 7 0 0 0 0 0 0 0 0 0 0 0 0
E. krishnani 0 0 0 0 1 0 3 3 0 0 0 0 0 0 0 0
Perophora
formosana 3 1
1
0 7 0 0 0 0 0 0 0 0
1
1 5 5
1
3
Table 4: Seasonal variations of members of Styelidae [ individuals/m2 (mean values)] at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Eusynstyela tincta 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
Styela canopus 5 7 5 2 1 0 1 6 0 0 0 0 1
2 0
1
3
2
0
Symplegma oceania 3 2 3 2 0 0 0 0 1
7
1
3
1
6
1
8 0 1 5 4
Botrylloides
magnicoecum 5 3 2 4 0 0 0 0 6
1
6
1
6
1
3 0 0 1 2
B.leachi 0 0 0 0 0 0 0 0 3 3 4 3 0 0 0 0
B. chevalensis 0 0 0 0 3 0 4 4 0 0 0 0 0 0 0 0
Table 5: Seasonal variations of members of Holozoidae[ individuals/m2 (mean values) ]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Distaplia nathensis 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Table 6: Seasonal variations of members of Didemnidae [ individuals/m2 (mean values) ]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 1 Station 1 Station 1
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1101
Diplosoma
swamiensis 2 3 1 0 5 2 0 0 0 0 0 0 5 0 9
1
9
Didemnum
psammathodes
1
3
1
6
1
2
1
1
2
6
3
8
6
2
4
8
1
8
1
1
7
0
6
4 0 0 0 0
Lissoclinum fragile 1
0
1
5
1
0
1
3
1
3 6
3
1
2
4 0 0 0 0 3 5
2
7
2
2
Trididemnum clinids 6 4 1
1 6 5 7 4 1 0 0 0 0 5 0 0 0
Table 7: Seasonal variations of members of Polycitoridae[ [ individuals/m2 (mean values) ]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Eudistoma
lakshmiani 0 0 0 0 0 0 0 0 0 0 0 0 6
1
8
1
5
1
9
E. viridi 0 0 0 0 9 1
3
2
0
1
2 0 0 0 0 0 0 0 0
Table 8: Seasonal variations of members of Polyclinidae[ individuals/m2 (mean values) ]at
stations 1,2,3 and 4 in Thoothukudi coast.
Species name
Station 1 Station 2 Station 3 Station 4
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
P
o S
P
r M
Polyclinum indicum 0 0 0 0 0 2 0 0 2
2
2
0 2
1
8 3 0 0 0
P.madrasensis 0 0 1 0 3 7 1
5 5
1
3
1
4
1
4
1
3 0 0 0 0
Members of two families Didemnidae and Styelidae were commonly available at all the
stations of study area. There was no representation of the family Polycitoridae at station 1,
Holozoidae and Ascididae at station 2, Holozoidae, Polycitoridae, Perophoridae, Ascididae
and Pyuridae at station 3 and Holozoidae, Ascididae and Polyclinidae at station 4. Ascidia
sydneiensis, A. gemmata, Phallusia nigra, P. arabica P. polytrema, Eusynstyela tincta and
Herdmania pallida at station 1, Eudistoma viride at station 2, Botrylloides leachi at station 3
and Eudistoma lakshmiani at station 4 were highly dominant and restricted. More number of
species ( 18) were recorded during premonsoon season at station 1 and less number(5) was
recorded during summer season at station 4.Senescence and recession period of colonial
ascidian Polyclinum indicum was noted at station 3 during early summer.
The abundance of ascidians varied from 721/m2(station 1) to 1252/m
2(station 4). The
Margalef’s species richness ranged from 2.91 (monsoon season) to 3.98 (premonsoon
season). The H’ value was in between 1.84 and 3.50, while the evenness value ranged from
0.71 to 0.94. The taxonomic diversity index was more (71.12) during postmonsoon season
and total phylogenetic index was higher (880) during premonsoon season. The variation in
taxonomic distinctness index was more (548.95) during premonsoon season and low (451.0)
during monsoon season. The values of various indices are given in the Tables (9-11) and
Figures (2-21).95% confidence funnel drawn for the variation in taxonomic distinctness
showed normal distribution of ascidians species and higher diversity at station 1, station 2
and station 4 but station 3 showed significant deviation. The 95% probability contours
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1102
(ellipse plot) (Figure 6) shows statistically deviation of all stations from station 1 in ascidians
diversity during summer season.
Table 9: Various Diversity indices of ascidians during monsoon season in Thoothukudi
coast (stations 1 -4).
Table 10: Various Diversity indices of ascidians during summer season in Thoothukudi
coast (stations 1 -4).
Table 11: Various Diversity indices of ascidians during postmonsoon season in
Thoothukudi coast (stations 1 -4)
Table 12: Various Diversity indices of ascidians during premonsoon season in
Thoothukudi coast (stations 1 -4).
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1103
.
Figure 2: 95% confidence funnel
showing lower diversity of ascidians at
station 3 during summer season as this
station deviates from the normal
distribution
Figure 3: 95% confidence funnel
showing poor diversity of
ascidians at station 3 during
Premonsoon season as this station
deviates from the normal
distribution.
Figure 4: 95% confidence funnel
showing lower diversity
of ascidians during monsoon season at
station 3 as this deviates from the normal
distribution
Figure 5: 95% confidence funnel
showing lower diversity of
ascidians at station 3 during
postmonsoon season as this
station deviates from the normal
distribution
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1104
.
Figure 6: 95% probability contours
(Ellipse plot) showing statistically
deviation of all stations from station 1
in ascidians diversity during summer
season.
Figure 7: 95% probability contours
(Ellipse plot) showing significant
deviation of station 3 from other
stations in ascidians diversity during
premonsoonseason.
Figure 8: 95% probability
contours (Ellipse plot)
showing significant deviation
of station 3 from other
stations 1,2 and 4 in ascidians
diversity during monsoon
season
Figure 9: 95% probability
contours (Ellipse plot) showing
significant deviation of station 3
from other stations 1,2 and 4 in
ascidians diversity during
postmonsoon season
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1105
Summer
1
2
3
4
Cu
mu
lative
Do
min
an
ce
%
Species rank
0
20
40
60
80
100
1 10 100
Premonsoon
1
2
3
4
Cu
mu
lative D
om
ina
nce%
Species rank
0
20
40
60
80
100
1 10 100
Monsoon
1
2
3
4
Cu
mu
lative
Do
min
an
ce
%
Species rank
0
20
40
60
80
100
1 10 100
Postmonsoon
1
2
3
4
Cu
mu
lative
Do
min
an
ce
%
Species rank
0
20
40
60
80
100
1 10 100
.
.
Figure 10: The dominance plot
showing the curve for the station 1
indicating rich diversity of ascidians
during summer as more number of
species lies on the lower curve
Figure 11: The dominance plot showing
the curve for the stations 2,3 and 4
indicating less diversity of ascidians than
station 1 during Premonsoon season as
the curves lies over the first from the
bottom
Figure 12: The dominance plot
showing the curve for the station 1
indicating rich diversity of ascidians
during monsoon as more number of
species lies on the lower curve
Figure 13: The dominance plot
showing the curve for the stations 2,3
and 4 indicating less diversity of
ascidians than station 1during Post
monsoon season as the curves lies
over from the bottom
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1106
Figure 14: Dendrogram of ascidians showing grouping of stations. Station 1 and station 2
Figure 15: Dendrogram of ascidians showing grouping of stations. Station 2 and station 3
are forming a group with maximum similarity and station 3 linked with them. Station 4 get
linked with station 3 with low similarity during summer season are forming a group with
maximum similarity and station 1 and station 4 forming a group with maximum similarity.
Both are getting linking at a very low similarity during premonsson season.
Figure 16: Dendrogram of ascidians recorded in various stations showing grouping of
stations. Station 1 and station 4 forming a group with more similarity and station 2 joining
with station 1 and station 3 is getting linked at a very low similarity level during monsoon
season.
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1107
Figure17: Dendrogram of ascidians recorded in various stations showing grouping of
stations. Station 1 and station 2 forming a group with the maximum similarity and station 4
joining with them and ultimately station 3 is linked at a very low similarity level during
postmonsoon season.
Figure 18: MDS for ascidians recorded during summer season in stations (1,2,3 and 4) of
Thoothukudi coast showing excellent ordination and goodness of fit(stress:0).
Figure 19: MDS for ascidians recorded during premonsoon season in stations (1,2,3 and 4)
of Thoothukudi coast showing excellent ordination and goodness of fit (stress:0).
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1108
Figure 20: MDS for ascidians recorded during monsoon season in stations (1,2,3 and 4) of
Thoothukudi coast showing excellent ordination and goodness of fit(stress:0).
Postmonsoon
1
2
3
4
Stress: 0
Figure 21: MDS for ascidians recorded during postmonsoon season in stations (1,2,3 and 4)
of Thoothukudi coast showing excellent ordination and goodness of fit(stress:0).
Discussion
In the present study, the maximum species of ascidians was recorded at station 1, the harbour
area of Thoothukudi. This may be due to the availability and stability of various suitable
substrates like pebbles, permanent barges, oyster beds, boulders, submerged concrete
structures, blocks etc. for ascidians to settle. Abdul Jaffar Ali (2004) reported that population
density of Phallusia nigra was higher in the harbour area of Thoothukudi Coast due to the
availability of different kinds of substratum. Further Thoothukudi, being one of the major
maritime ports, serves as gateways for invasion of new species through hulls of ships and
ship’s ballast water. Ship hulls help in disseminating exotic species which settle in harbour
(Monniot and Monniot, 1985 and Tamilselvi et al., 2011). Number of evidences also support
this fact that worldwide shipping has introduced exotic species into many ports (Monniot and
Monniot, 1991and 1994., Carlton et al., 1993., Hewitt et al., 2004).
The minimum number of ascidians recorded at Station 3 could be correlated with the
presence of few available substratums like sandy mud. Further the December 2000
monsoonal flood waters and cyclonic storms altered the nature of the substratum by the
deposition of sand and silt in this region. This extreme substratum instability could have
prevented the attachment of sedentary forms in the intertidal zone, which then alter animal
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1109
population of the habitat. Young (1989) also reported that habitat stability appears to be
enormously important for survivorship and sand movements and excessive siltation have
adverse effects on both adults and juveniles. The station 3 is also prone to heavy shore
currents and periodic upwelling. These physical disturbances might have affected the
settlement of larvae. Higher Evenness value at station 3 represents poor diversity and which
in turn related to the availability of very few suitable substrata. Clampitt (1970, 1973),
Harman (1972) and Wise and Molles (1979) reported that substratum is a significant
ecological factor influencing the distribution of organisms.
Margalef’s diversity index commonly varies between 1 and 5 and the larger the index value
indicates a more healthy body of water. In the present study, Margalef’s more species
richness was more at Station 1 reflects the suitability of habitat for the organisms and a
relatively stable community due to the presence of stability and availability of the substrates.
Further more this station is situated within two parallel arms and maritime port area with
limited wave action favouring the settlement of larvae. Kott (2002) and Tamilselvi et al.,
(2011) reported that the provisions of maritime and other installations associated with
commercial harbour and other activities provide additional habitats for ascidian species.
The similarity in species composition and abundance of ascidians in adjacent stations showed
high similarity, whereas distant stations getting linked showed low similarity level. Species
structures were relatively constant and slowly changed within limits and hence there were no
large fluctuations in species from season to season. This might be due to the fact that tadpole
larvae settle at a suitable substratum near the parent colony after a brief planktonic life.
In the present study, lower number of species was recorded during summer in all stations;it
reflecting the unfavorable environmental condition for the ascidians which undergo recession
and enter into resting period as reported by Turon and Becerro (1992). The observed
senescence and recession period of the colonial ascidian Polyclinum indicum during early
summer was corresponding with similar findings by Davis and White (1994) who reported
that the colonial ascidian Botrylloides magnicoecum becomes senescent in late spring and
early summer.
The month wise and seasonal variations in individual and number of species in the present
study at different stations might be due to different longevity patterns of the organisms and
also due to various reproductive cycles. Rinkevich et al. (1993) reported that the life history
traits such as longevity and reproduction are subjected to adaptation to environmental and
biotic conditions, so that the species may show phenotypic plasticity. There are many
examples among ascidians which show differences in life history trait during different
seasons between populations separated by only 60km (Ciona intestinalis – Millar, 1952;
Dendrodoa grossularia – Millar 1954; Podoclavella mollucensis – Davis, 1989) or even in
the same area (Botrylloides sp. – Rinkevich et al., 1993; Aplidium glabrum – Durante and
Sebens, 1994). Turon (1988) also demonstrated a relationship between reproductive periods
and the latitudinal distributions of ascidians.
The great majority of the species belonging to Styelidae, and Didemnidae with wide
distribution in Thoothukudi Coast, might be due to their continuous breeding activity of the
species. These findings are in accordance with that of Renganathan (1983d, 1983e, 1984f)
who reported continuous breeding activity in Eudistoma viride, Didemnum psammathodes,
Eudistoma lakshmiani and Lissoclinum fragile in Thoothukudi Coast. Goodbody (1961)
observed that Ascidia nigra, Diplosoma macdonaldi and Symplegma viride settled
throughout the year in Kingston harbour, Jamaica though not at a uniform rate.
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1110
In the present study, certain species such as Distaplia nathensis, Diplosoma swamiensis,
Ecteinascidia venui, Perophora formosana, Phallusia nigra, P. Polytrema, P. arabica,
Ascidia sydneiensis, Eusynstyela tincta & Microcosmus curvus at Station1, Polyclinum
indicum, Trididemnum clinids, D. swamiensis, ,S. canopus , S. oceania at Station 2, D.
swamiensis, L. fragile, and S. canopus and at Station 4 showed sudden disappearance during
certain months, heterogenous distribution and sporadic occurrence during certain parts of the
year and this could be correlated to the direct and indirect influence of biotic and abiotic
factors of the environment directly or indirectly affecting their distribution and abundance.
Many workers reported that the environmental variables are the most important factors in
determining ascidian distribution such as temperature(Namaguchi et al., 1997)
salinity(Vazquez and Young 1996 and 2000), light (Forward et al., 2000 and Tsuda et al.,
2003) hydrodynamics (Holloway and Connell, 2002) competition (Lambert, 2000; G.
Lambert 2001) and predation (Castilla et al., 2002).
The dominance and restricted distribution of Herdmania pallida and all the species belonging
to family Ascididae at station 1, Eudistoma viride at station 2, Botrylloides leachi at station 3
and Eudistoma lakshmiani at station 4 are worth mentioning. Though a solid reason could not
be pinpointed, it could be attributed to various physical parameters especially the
sedimentary dynamics, availability of food, current intensity, wave exposure etc. as reported
by Rocha et al. (1999).
The 95% funnel drawn for the variation in taxonomic distinctness observed in the present
study showing normal distribution of animals and higher diversity at stations 1, 2, and station
4 due to the presence of stable substratum but station 3 showed significant deviation. Station
3 is vulnerable to pollution as this station, situated near the fish landing centre, receives
pollutants such as oil spillage and grease from boat yards domestic sewage, industrial
effluents, fly ash from TTPS and land runoff. These factors might directly or indirectly
inhibit the settlement of larvae and not conducive for the survival and growth of organisms.
Kott (2002) reported that fertilizer, insecticide and other organic pollutants and suspended
sediments in terrestrial run-off could well affect filter feeding organisms.
To conclude, the economic and ecological value of habitat is mainly dependent on the
species diversity and its conservation. Ascidians are considered as non-commercial
organisms till 20th
century and after that, when the first marine natural product didemnin B
was obtained from the tunicates entering human clinical trials, followed by ET743 isolated
from Ecteinascidia turbinate (Rinehart,2000), Aplidine from Aplidium albican (Hafner,2003),
Diasonamide A and Vitilevuamide isolated from Didemnum cuculiferum and Polysyncraton
lithostrotum, scientists have paid great attention on this group. Comprehensive knowledge of
the diversity and seasonal occurrence of ascidians would be helpful in predicting their annual
settlement, which would ensure success in the culture of commercially and pharmacology
important ascidians and also in the formulation of suitable control measures. In the present
study well marked diversity as well as seasonal variations of tunicates recorded at four
stations in Thoothukudi coast indicates the rich diversity of ascidians. This unique resource
in its locality has to be preserved not only for sustainable utilization but also to conserve
biological heritage. More and more areas should be investigated in around Thoothukudi as
this area is being very close to the Gulf of Mannar Marine Biosphere Reserve and has been
chosen as biosphere reserve for its biological and ecological uniqueness. The present data
gives the basic information on the diversity of tunicates which would form a useful tool for
ecological assessment and monitoring. This study suggests that Thoothukudi coast offers a
Diversity and seasonal variations of Class Ascidiacea in Thoothukudi coast, India
Tamilselvi. M, Abdul Jaffar Ali. H, Thilaga. R.D
International Journal of Environmental Sciences Volume 3 No.3, 2012 1111
unique opportunity for future research on the ecology and autecological studies of
commercial species of the Class Ascidiacea.
Acknowledgment
We
thank our mentor Dr.V.Sivakumar, Associate Professor, Department of Zoology,
V.O.Chidambaram College, Thoothukudi for guiding and encouraging us to carry out this
work. Our sincere thanks to Dr.S. Ajmal Khan, Emeritus Professor, Centre of Advanced
Study in Marine Biology, Annamalai Univeristy, Parengipettai for his kind assistance in the
statistical interpretation of the data and valuable guidance. The first author wishes to express
thanks to The Principal, V.V.Vannniaperumal College for Women, Virudhunagar for
encouragement.
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