Diversity and seasonal variations of Class Ascidiacea in

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.

[email protected]

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.




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




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


Species name


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


Species name


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


Species name


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


Species name


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


Species name


P

o S

P

r M

P

o S

P

r M

P

o S

P

r M

P

o S

P

r M




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


Species name


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


Species name


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




(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).




.

Figure 2: 95% confidence funnel

showing lower diversity of ascidians at

station 3 during summer season as this

station deviates from the normal

distribution


showing poor diversity of

ascidians at station 3 during

Premonsoon season as this station

deviates from the normal

distribution.


showing lower diversity

of ascidians during monsoon season at

station 3 as this deviates from the normal

distribution


showing lower diversity of

ascidians at station 3 during

postmonsoon season as this

station deviates from the normal

distribution




.

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




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


showing the curve for the station 1

indicating rich diversity of ascidians

during monsoon as more number of

species lies on the lower curve


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




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.




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).




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




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.




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




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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