Andaman and Nicobar archipelago located in the central part of the Bay of Bengal consists of 572 islands. Southern tip of this archipelago is located just at 145 NM from the northern side of Indonesia and 750 NM distance from the eastern coast of India. This island is scarcely populated than the mainland India. This pristine environment supports establishment of well diversified coral communities. This archipelago is one among the 12 mega-biodiversities and also one among the 25 hotspots of the rich and highly endangered eco-regions of the world. Among the Asian countries, India is the only one country that has a long record of inventories of coastal and marine biodiversity dating back to at least two centuries.

The research history of malacological studies in India is among the oldest one which was initiated by the Asiatic Society of Bengal during the year 1784 and made a repository in the Indian Museum, Calcutta in the year 1814. Benson published a total of 90 research papers which was mainly concerned land and freshwater mollusks of the Indian subcontinent between 1830-1865 [1] . Till date, 3370 species of marine mollusks have been recorded in India, out of which 1282 species are from Andaman and Nicobar Islands [2] . The majority of mollusks are present in the marine biotopes and they occur from the backwater zone, mangroves, intertidal and shelf in deeper waters. Mollusks have been a favorite candidate for the research in the early days, especially those available on rocky shores and inter-tidal zones as they are plentiful of animal, moderately slow moving and easy to identify [3] [4] [5] . They comprise an important component of intertidal fauna and flora [6] .

Among the mollusks, gastropods are more important in the coastal populations’ economy, i.e. as a shell-craft industry. Over and above, the marine gastropod resources in India consisted of different types of species which are exploited regularly for various purposes like drugs, ornamental purposes as well as for their meat. Andaman and Nicobar Islands, the gastropod diversity are high, due to the majority of shores are rocky. The wet rocky shore promotes algal growth, which is ultimate for feeding ground for gastropod growth and development leading to more diversity. Further, the mangrove environment also provides ideal conditions for the productivity of gastropods [7] .

The global warming, anthropogenic activities, industrial and domestic pollution, etc., have accelerated the loss of coastal and marine biodiversity components over the last few decades which has been of great concern. However, except global warming, the other factors were of least concern with reference to Andaman and Nicobar Islands biodiversity due to a pristine environment. Therefore, exploration of biodiversity in these islands is essential to create a baseline data for record and future research. In this regard, gastropods are a significant indicator of environmental changes, hence, an attempt had been made to understand a comprehensive gastropod diversity by the way of studies on selected locations of the south to north Andaman coast lines.

Gastropoda species were collected from the coasts of Carbyns Cove, Rangat, Mayabunder and Diglipur for a period of one year in three prevailing seasons of Andaman and Nicobar Islands. They are SW monsoon, NE Monsoon and Non rainy Seasons. The collected samples were identified up to species level and their data were converted into percentages (Table 1). The photographs of these species were provided as Figures A1-A8.

Based on this study, among the four stations, seventy one species belonging to fifty two genus and thirty three families of gastropods were observed. Among the seventy one species, 38 species fell in unique category such that it may be noticed in any one of the stations, in any one of the season, i.e. their appearances/dis- appearance were not found to be site specific or seasonal specific (Table 2). Among them, 10 species available during the NE monsoon season in the station Rangat followed by SW monsoon season in the station Rangat (08), SW monsoon season in the station Mayabunder (05), NE monsoon season in the station Carbyns Cove (04), NE monsoon in the station Mayabunder, SW monsoon in the station Diglipur, represented 03 species each, Non rainy season of Mayabunder and Diglipur observed 01 species each, NE monsoon for Diglipur and Non rainy season in the station Rangat and Carbyns Cove noticed 01 species respectively, and the SW monsoon season in the station Carbyns Cove represented a total absence of gastropods.

Out of the remaining species, 20 species were observed in two occurrences by the way of any two seasons or any two locations or one season in two locations (Table 3). In these, NE monsoon in the station Rangat represented 09 species. Non Rainy season of Mayabunder (04) and SW monsoon in the station Rangat represented (07) species, followed by SW monsoon Mayabunder (05), Non Rainy season of Diglipur (02), NE monsoon of Diglipur (01), SW monsoon of Diglipur (03), NW monsoon of Carbyns Cove (02), SW monsoon of Carbyns Cove (02) and 1 species in Non rainy season of Rangat and Carbyns Cove were observed.

The species Tylothais virgata only observed during the NE monsoon of all the stations except Diglipur. Clypeomorus bifasciata species noticed only in the fifty percent of the seasons of the study period (NE Rangat, NRS Mayabunder, NE Diglipur, NRS Diglipur, NE and NRS of Carbyns Cove. Pollia undosa species were observed in NE monsoon season of Rangat and Diglipur as well as SW monsoon at Diglipur (Table 4).

Trochus radiates noticed in the NE monsoon of Rangat and Carbyns Cove

and SW monsoon period in Mayabunder and Rangat. Chicoreus brunneus observed in SWM of Rangat, Mayabunder and Diglipur as well as NEM of Carbyns Cove stations. SWM of Mayabunder, NEM of Rangat and Carbyns exhibited Monodonta australis species and in Diglipur it had been noticed in Non rainy season and SW monsoon. Harpa major species were noticed in NEM and SWM of Rangat and Carbyns Cove (Table 4).

Except NEM in Mayabunder and NRS of Carbyns Cove all the remaining seasons represented by Nerita albicilla (Table 4). This is the only species observed in almost all the stations with the majority of the seasons (Table 4).

The NEM in Rangat, Diglipur and Carbyns Cove as well as NRS in Diglipur and SWM in Mayabunder and Diglipur represented the species Turbo bruneus, i.e. all the three seasons in Diglipur this species was present. Nerita oryzarum was observed during the period of NEM of Rangat, Diglipur and Carbyns Cove,

SWM in Rangat and Diglipur and NRS in Mayabunder (Table 4).

The station Carbyns Cove exhibited a total of nineteen species consist of nine families. Out of nineteen species, single occurrence was noticed in 15 species and dual occurrence noticed for 4 species. A total of 24 families was missing in this station.

The station Rangat reported 42 species from 21 families. Out of 42 species single seasons were noticed for 32 species and dual occurrence noticed in 09 species and one species in all seasons. Twelve families were missing from this station.

The gastropods of 29 species belonging to 17 families were observed at Mayabunder station. Out of these 29 species, single occurrence noticed in 25 species and dual occurrence noticed in four species. There were 16 families missing.

Diglipur station reported 20 species belonging to 10 families in all the seasons. Out of 20 species, 13 species single time reported and two and three time presence noticed respectively 05 and 02 species. In this location 13 families were missing.

The study period represented the highest number of species (60) during the NE monsoon represented than remaining seasons. Next higher number of species (53) noticed in the SW monsoon and lowest numbers noticed in Non rainy season (26).

The results of the studied gastropods in the Primer software and the univariate analysis (Table 5) suggested that highest Margalef’s Species Richness Index (6.080) noticed during the NE monsoon period of Rangat (29 species) and the lowest (0.434) noticed during Non Rainy Season at Carbyns Cove and Rangat (3 species). However, the Pielou’s Evenness Index represented the maximum of 1.000 for the Carbyns Cove Non Rainy Season samples (3 species) and lowest (0.404) noticed for the Rangat (3 species) Non Rainy Season. The Shannon- Wiener Index represented the maximum (3.067) for the NE monsoon period of Rangat (29 species) and the lowest (0.444) noticed for the Rangat (3 species) Non Rainy Season. The Simpson Diversity Index supports the Shannon-Weiner Index.

The group average of the Cluster plot (Figure 2) suggested that three major clusters divided in one independent character and two with sub clusters. The one independent cluster represented the Non Rainy Season of Carbyns Cove (Cluster A). The second cluster with two sub clusters represented NE and SW monsoon periods of Mayabunder (Cluster B-B1, B2). The third cluster (Cluster C) with nine sub clusters has represented by five units of the remaining seasons and stations. The first unit (C-1) has two sub-sub-clusters (C-1-1 and 2) for NRS Rangat and SWM Carbyns Cove. The unit two (C-2) has two sub-sub-clusters represented NEM Digilipur and NRS Diglipur.

The unit 3 (C-3) also has two sub-sub clusters with SWM Digilipur and NEM Carbyns Cove. The unit 4 (C-4) represented only one season that is NRS Mayabunder. The last unit 5 (C-5) has two subdivisions represented NEM and SWM Rangat.

Based on the above results it was inferred that the station Rangat was highly enriched with gastropod species when comparing all the four stations followed by Mayabunder, Diglipur and Carbyns Cove stations. However, based on the occurrence of the species, it was noted that the stations Rangat and Carbyns Cove may be similar in environmental condition than the remaining two stations. Similarly, NE and SW monsoon plays a major role in the diversity and distribution of species in Rangat stations than in the Non rainy season. Mayabunder and Diglipur stations exhibited less diversity and distribution in NE monsoon than SW monsoon.

However, the Non Rainy Season shows diversity and distribution in between the above rainy seasons. Carbyns Cove represented SWM and NRS less favorable for diversity and distribution than NEM period.

Out of seventy one species studied, 10 species identified only upto genus level. The remaining 61 species, 57 species already reported in Andaman and Nicobar Islands by Rao (2003). The species Nerita oryzarum was reported by Ragunathan and Venkatraman [18] and the other three species Turbonilla felicita, Vokesimurex tryoni and Batillaria multiformis were not reported in these Islands.

The west coast of India in Raigad District, Maharashtra exhibited 14 species occurrence from the studies of Kade and Mane [19] . Haragi et al. [20] reported 7 species at the Karwar coast of Karnataka. Seven species of Charwad coast (Gujarat) reported by Vadher et al. [21] . Goa coast exhibited seven species of occurrence [6] . Elaiyaraja et al. [22] reported four similar species in the study from Palk Bay region. Chelladurai et al. [23] , reported one studied species from the Gulf of Mannar, Tamil Nadu region. Sakthivel and Fernando [24] studied five species in the present study from Mudasal Odai and Nagapatinam coastal regions. Arumaugam et al. [8] reported eighteen species of the present study in the Great Nicobar Coastal environment. Priyankadevi et al. [25] reported 12 species of the present study in Avis Island and Karmatang beach of Mayabunder.

The station Rangat, Mayabunder, Diglipur and Carbyns Cove represented 42, 29, 20 and 19 species among the studied species. This suggested that Rangat station has an exposure of rocky outcrop which may provide a better niche for larger diversity of gastropod species. Even though Carbyns Cove also has the similar exposure because of little areal exposure during the low tide time may be reduced the population of this species. The studied Mayabunder location may have rocky and mangrove exposure support the presence of Littoraria undulata exclusively in this location and have next in concentration of diversity. Diglipur station was covered with coralline exposure than the rock exposure has fallen in between the Carbyns Cove and Mayabunder diversity status. Chelladurai et al. [23] , and Elaiyaraja et al. [22] , reported that the coralline outcrop has more amount of diversity during the non rainy season also proved in this study location where the similar outcrop exposed, i.e. the station Diglipur which exhibited comparatively equal or more diversity during the non rainy season than in the monsoon period.

These studies well follow the existing inference from the world wide study pattern of the gastropoda. As reported by the Sanpanich et al. [26] and Suresh et al. [27] , Littoraria undulata only occurred in the rocky outcrop with mangrove environment. Ramadoss [28] , Tan and Clements [29] , Arumugam et al. [8] , Haragi et al. [20] , Khade and Mane [19] , Sorensen [30] , Miloslavich et al. [31] and David [6] was reported rocky outcrop species were also present in this study area also in the same environment. Bhadja [32] , David [6] and Vadher et al. [21] , reported that diversity is more in the period of monsoon than in non rainy seasons of rocky outcrop environment also supported in this present study that the station Rangat exposed to 40 species during the monsoon (SW and NE) period. Yaninek [33] reported that Conus ebraeus, more abundant in the higher intertidal zone than in the outer zone, which also true in the present study.

The results of univariate analysis based on Margalef’s Species Richness Index, Pielou’s Evenness Index, Shannon-Wiener Index and Simpson Diversity Index supported each other for the distribution of gastropods in the study locations for all the seasons. The cluster analysis also grouped the unique character of occurrences with reference to locations and seasons. While comparing these clusters, it was noted that that the individual clusters Cluster A and Cluster B has no similar species between them, but it shared similarities of the species with C1 and C2 clusters. The cluster B represented single common species (Nerita albicilla). Cluster C, among all the sub clusters (5 Nos.), the cluster four and five have three common species Nerita albicilla, Nerita oryzarum and Nerita polita. The sub cluster three, four and five showing two common species Nerita albicilla and Nerita oryzaraum and three and four exhibited two common species Nerita albicilla and Turbo brunneus. However, the cluster two and five exhibited one common species are Nerita albicilla. Turbo species exclusively in Cluster A among the three available species and Cluster B exhibited twelve species exclusively among the 20 available species. Total forty nine species exclusively found in Cluster C among 59 which can be divided into five sub clusters.

The present study of gastropods distribution in the South, Middle and North Andaman groups of Islands suggested that there are 71 species belonging to 52 genus and 33 families. At any one of the time and any one of the locations, only one occurrence was noticed for 38 species and remaining 33 species were overlapping with respect to stations and seasons. Nerita albicilla observed at all the stations with the majority of the seasons except NEM of Mayabunder and NRS of Carbyns Cove. Turbo species exclusively in Cluster A among the three available species and Cluster B exhibited twelve species exclusively among the 20 available species. Total forty nine species exclusively found in Cluster C among 59 which can be divided into five sub clusters. This study also concluded that three species (Turbonilla felicita, Vokesimurex tryoni and Batillaria multiformis) were new to the Andaman Islands and among them two species (Vokesimurex tryoni and Batillaria multiformis) were not recorded any part of India.

The authors thank the Central Marine Living Resources and Ecology, Ministry of Earth Sciences, Kochi for funding this work (MOES/CMLRE/10-ITIS/5/2012, Date: 01/10/2012). They also acknowledge the authorities of Pondicherry University for providing the facilities needed for the execution of this project.

Jeeva, C., Mohan, P.M., Sabith, K.K.D.B., Ubare, V.V., Muruganantham, M. and Kumari, R.K. (2018) Distribution of Gastropods in the Intertidal Environment of South, Middle and North Andaman Islands, India. Open Journal of Marine Science, 8, 173-195. https://doi.org/10.4236/ojms.2018.81009