New distributional data on ascidian fauna (Tunicata: Ascidiacea) from Mandapam coast, Gulf of Mannar, India

Abstract Background Ascidians play a key role in the ecology and biodiversity of marine ecosystem. Ascidians can be transported in ship ballast water and while attached to ship and boat hulls. Heavy traffic by domestic and international ships as well as cargo vessels between the major and minor ports warrants continuous monitoring for new introductions of ascidians. The Mandapam coast is situated in the Gulf of Mannar, India, a marine hot spot area in the Indian Ocean which provides an environment suitable for the settlement of ascidians. New information A total of 30 species of ascidians were reported from Mandapam coastal waters, of which 26 species were new to the study area and five species: Ecteinascidia turbinata, Eudistoma carnosum, Trididemnum caelatum, T. vermiforme and Didemnum spadix, were new to India.


Introduction
Ascidians (Class: Ascidiacea and subphylum: Urochordata), commonly called tunicates, are a common, diverse group among the macro fouling communities in marine ecosystems, that attach to natural and artificial substrates in the intertidal and subtidal zones of coastal habitats throughout the world. They are one of the key ecological groups because of their invasive potential. Ascidians have the potential to produce new lead molecules with significant pharmacological activities (Davidson 1993;Rinehart 2000;Haefner 2003 andJain et al. 2008). Some ascidians have been used for their nutritional value as food for people in many parts of the world including India (Nanri et al. 1992 andTamilselvi et al. 2010). Certain solitary ascidians serve as indicators of water quality (Abdul Jaffar Ali 2004;Tamilselvi 2008;Abdul Jaffar Ali et al. 2011 andAbdul Jaffar Ali et al. 2015b).
India has a rich natural heritage and nurtures a unique biodiversity, placing it among the 17 most biodiverse countries (Venkataraman 2003). The Gulf of Mannar, located in the southeast coast of India, is a hot spot for Indian marine biodiversity and recognized as Marine National Park. The site provides natural and artificial substrata for the successive settlement, growth and breeding of ascidian species throughout the year.
Mandapam (Latitude 9°28'N and Longitude 79°15'E) is located in Gulf of Mannar and experiences heavy traffic of fishing and defense vessels from various major and minor ports along the Indian coast. Tidal exchange in the area is seasonal. Direction and force of the monsoonal winds influence this station, since the coast line in the east-west direction.

Materials and methods
The study was carried out from March 2014 to February 2015 at Mandapam, India. Collections were made randomly during the study period at intertidal beds and in shallow water regions. Hand tools were used to remove animals from solid surfaces like pillars of jetties, small rocks and hulls of fishing vessels. Snorkeling was also employed to collect ascidians at 1-2 meter depths. Collected specimens were narcotized with menthol and then preserved in 10% buffered formalin in seawater. The specimens were sorted and identified to species or the lowest possible taxonomic level using taxonomic keys (Sebastian 1956;Tokioka 1967;Millar 1975;Kott 1985;Renganathan 1986;Monniot andMonniot 1996 and. Data set of distribution of ascidians throughout the world was obtained from WoRMs.

Distribution
Djibouti, South Pacific Ocean, Tanzania.

Discussion
A total of 30 species of ascidians, comprising 6 families and 11 genera, from the Mandapam water has been reported in the present study (Suppl. material 1). Out of 30 species, 26 were new to this station, among which 5 species: Ecteinascidia turbinata, Eudistoma carnosum, Trididemnum caelatum, T. vermiforme and Didemnum spadix, were reported for the first time in India. The other 4 species were previously documented at the study area and are considered non-native species. The total number of ascidian species (n=30) is greater than previously documented (n=19) in 2003, thus increasing biodiversity. This new entry of ascidians to the study station could possibly be explained by invasiveness of ascidians and vectors such as the hulls of ships and ballast water (Byers 2002). Heavy traffic of shipping and fishing vessels acts as an important vector for intra and inter coastal spread of invaders (Johnson et al. 2001, Wasson et al. 2001, Darbyson 2009, Rocha et al. 2010).
Previously, a total of 19 ascidian species was reported from this station (Meenakshi 1997, Meenakshi 1998, Meenakshi 1999, Meenakshi 2002, Meenakshi 2003, Meenakshi 2006, Meenakshi 2009, Renganathan 1984a, Renganathan 1984b, among which only four species (Eudistoma ovatum, E. reginum, E. tumidum and Polyclinum fungosum) were encountered in the present study. The increasing number of new entries of ascidians and absence of previously reported species at this station may be due to changes in physicogeographical structures such as expanding of fishing harbour, establishment of new jetties and heavy traffic of fishing vessels.
The diversity of ascidians is influenced by the development of coastal patterns and environmental impacts (Carman et al. 2007). Ascidians are common inhabitants of harbours and marinas in both temperate and tropical waters (Monniot et al. 1991). They can easily be translocated by ships as well as boats and also through ballast water due to their motile larvae and sedentary adults. The dimension of ascidian diversity and increased invasive state of ascidians is influenced by coastal shipping patterns (Carman et al. 2011).
The Mandapam station has lots of substrata such as jetties, embedded rocks, small stones, fishing and coastguard vessels providing a suitable environment for the settlement of ascidians in a subtropical habitat.
Members of the family Polyclinidae occured in huge numbers throughout the study period with maximum colony size during summer season (March-May). Ecteinascidia venui was recorded in large numbers during premonsoon season (June-August). Ascidians are seasonal recruiters (Tamilselvi et al. 2012). Other ascidian species had sporadic occurrences throughout the study period.