Phuket Marine Biological Center Special Publication 26: 5-17 (2002)

Biogeography of Indian Marine Molluscs

R. N. Kilburn

Kilbum. R.N. 2002. Biogeography of Indian Maline Molluscs. - Phuket Marine Biological Center Special Publication 26: 5-17

Analysis of provisional lists shows the marine molluscan fauna of the Indian region to be predorninantly Indo-Polynesian, with perhaps 4-70lo endemism (the exact figure partly depending on whether fresh- and brackish water vicariates ofmarine groups are included). Significant differences in oceanographic conditions between the Bay ofBengal andArabian Sea are summarized, and attention is drawn to factors that have created potential barriers or frlter-routes. Based on these factors and on the limited faunal inventories available, four subregions are tentatively recognised as the basis fbr a working hypothesis. There appear to be two centres of endemism: (1) south-eastern India (i.e the Gulf of Mannar/Chennai area): it is suggested that the key elements may have vicariated in Palk Bay during periods of emersion of the Mannar she1f, and (2) the estuaries and backwaters of Orissa, West Bengal and Bangladesh, which serye as refugia fbr various euryhaline marine taxa that may have evolved under hyposaline conditions in the northem Bay of Bengal. Conservation prospects for these two centres are discussed.

R. N. Kilbum. Natal Museum, P/Bag 9070, Pietermaritzburg,320l, SouthAfrica E-mail : dkilburn@nms a.org.za

INTRODUCTION understanding of distribution patterns withrn The marine of India are arguably the Indian region. among the most extensively sampled of Indo- Before discussing its biogeography, it is first Pacific inveftebrate groups, yet are among the necessary to redefine "India". The modern most poorly analysed. Historically, many of state of India is not a biogeographic entity, the earliest described Indo-Pacific molluscs excluding as it does the closely adjacent areas were first collected in south-eastern India, the of Sri Lanka and Bangladesh, which share source being the Danish trading station much the same fauna. On the other hand it established at Tranquebar (now Tarangam- includes the Andaman Islands, whose bodi) between1620 and 1845. Most of these molluscan fauna clearly has strong Malesian were illustrated in the works of Martini ("Indo-Malaysian") affinities, with few if any (1769-1777) and Chemnitz (1780-1795), and true Indian elements (although a certain cited as type figures by generations ofbinomial amount of subspeciation and vicariance of workers. Indeed many of the species earlier sister groups demonstrates the absence of described by Linnaeus (1758) from "in Indiis" permanent barriers). Presumably Pakistan and certainly came from the same source. Yet Burma (Myanmar) should be included, but subsequent research has been patchy, and these countries are not considered here, in the identifications suffered from lack of access to absence of even basic faunal inventories for types and other primary sources. As a these regions. For similar reasons the east and consequence modern publications reveal little south coasts of Sri Lanka are excluded. Tropical Marine Mollu.sc Programme (TMMP)

To sum up, in this paper "India" or "the Mollusca ofc hennai (Nladras) Indian region", should be taken to cover the Ara [rian Endemic immediate coastal zones of lndia, adjacent Sri Lanka and Bangladesh to a depth of 200 m, but to exclude the Andaman and Nicobar W. Indian Archipelagoes. Ocean

BIOGEOGRAPHIC RELATIONSHIPS OF THE INDIAN MARINE REALM Although they did not consider the molluscan Malesian (1) fauna, Briggs (1974,1995) and Hayden et al. (1984) included India in a wide Indo- Polynesian Marine Province, as distinct from Mollusca of Gulf of Mannar a Westem Indian Ocean one, the two provinces Bndemic overlapping at the entrance to the Arabian Arabian Gulf. Is this supported by existing molluscan W.Indian inventories or can an lndian subregion be Ocean distinguished? Such inventories are few, largely far from comprehensive and the older ones based on obsolete . However, an analysis of two published taxonomic lists is here offered, namely one for Chennai Malesi*n (Madras) given by Gravely (1941 and 1942), {2} and a manuscript collation of molluscan Charts I &2.The relative distribution (%) of a types of records from the Gulf ofMannar (basedmainly faunal elements along the east coast oflndia. Area 1: the on those published by Satyamurti (1952,1956) coast around Chennai (Coromandel coast). Area 2: the and Standen & Leicester (1906)). For these Gulf of Mannar from Adam's Bridge towards Cape highly provisional lists, I have updated Comorin, l.e. the southern tip of India. nomenclature and deleted synonyms; obvious are misidentifications are excluded, as Indonesia, Philippines and vicinity). Evident brackish/fresh-water species, pelagic molluscs Western Indian Ocean incursives (here (including cephalopods), families of restrictively defined as species known at least micromolluscs (for which identifications are from E.ast Africa and the Mascarenes, but and unreliable), and nudibranchs. The sparse apparently not reaching Malesia) comprise results for the two areas are oresented in charts perhaps 2 oh. This increases Io 7 o/o if Arabian and2. I elements are included. Endemicity is a maximum of I oA. (1) Chennai At least 85o/o of the modified list of (2) Gulf of Mannar approximately 500 species are true Indo- Here the identifications of the source lists Polynesian elements, occurring also in the are probably less accurate, and duplication of Malesian region (Thailand, Malaysia, records under different names is to be expected Phuket Marine Biologicnl Center Special Publication 26: 5-17 Q002)

(in fact Winckworth (1928) observed of Standen & Leicester's list, "their identifi- cations seem to me far from reliable"). Nevefiheless, overall results are comparable. Of the approximately 620 species, about B8% are Indo-Polynesian elements, ca 4 oA are Westem Indian Ocean (8% ifArabian elements are added), and endemicity is only 4 %. Endemicity percentages for south-east Indian molluscs thus appear to be in the order of 4-J o/o, which is not indicative of high local vicariance, and falls well shorl of the highly conservative l0 % acceptedby Briggs (1974) as sufficient to qualify recognition of a marine province. Analysis of the molluscan fauna confirms Briggs later conclusion (1995:2311 that "India and Sri Lanka . . .. are populated by wide-ranging species and possess few local endemics". Nevertheless. there is sufficient 7 l'larpul ina lappanica endemism to justify treating the molluscan 2 Tudicla spnllus biota of the Indian region as a minor "faunal 3 Cremnoconchus of the Indo-Polynesian region. This is subset" syiradr-c'nsis supported by the occurrence of several endemic marine genera. such as three species of the volute genus Harpulina (Fig.1) and the monotypic turbinellid gents Tudicla (Fig.2), plus a number of unique brackish to freshwater descendents of otherwise marine groups, such as the genera Cremnocortchus (Littorinidae) (Fig. 3), Chilkaio (Fossaridae), Scaphula (Arcidae) (Fig. a) and l,{eosolen (Solenidae or Cultellidae) (Fig. 5). The apparently small proportion of true westem lndian Ocean elements is unexpected, but may be con'elated with the reduction in species diversity across the Indian Ocean reported (Kilburn 1977) for bivalves, and presumably applicable to molluscs in general. Of course. it must be stressed that the percentage of pan-Indo-Pacific elements whose origin could be either lndian Ocean or Malesian is indeterminate in the absence of 1a Scaphula celo.r (inner surface) genetic evidence. Future studies will 4b Scaphula celox (outer surl'ace) oresumablv demonstrate the Arabian element i Neosolerr,rqurcdrr/r'iolis Tr"opical Marine Molhtsc Programnte (TMMP)

to be better represented on the west coast than mangrove genus C er i t hi d e a, p otentially easily on the east. It would appear that the Indian dispersed by rafting, but represented in lndia marine fauna is derived largely from the by the Malesian C. obtusa (Lamarck, 1822) Malesian area, which is widely acknowledged and C. cingulata (Gmelin, 1'791), but not by as a centre of taxonomic diversification and the sole East African representative, C. (Paulay 1997). accumulation de col I at a (Linnaeus, l7 61 ). Nevertheless. fluctuations in current THE INDIAN MARINE intensity and pattem over geological time have ENVIRONMENT obviously varied greatly. For example, Before discussing regional variation within the plankton deposition in sediments has shown lndian region, the overall oceanographic that pre-Holocene monsoons and associated environment will be briefly reviewed. To upwelling were stronger than at present generalise, the main environmental factors (Sheppard et al. 1992). A reduced current influencing the indian molluscan biota are: would facilitate isolation of populations and (1) a unique system ofseasonally-reversing resultant vicariance, whereas intensified flow monsoon culTents; would increase the influx of incursives and (2) differing oceanographic regimes on mixing of gene pools (but would conversely either side of the Indian peninsula; also strengthen upwelling, which could (3) presence or absence of filter routes (or accentuate temperature barriers). barriers).

(2) Contrasts: the Arabian Sea and (l) Monsoon cunents the Bay of Bengal Oceanographers have charled these currents Major differences occur between the surface in considerable detail (see for example Sewell water masses on opposite sides of the lndian (1938), Fairbridge et al. (1966),Wyr1ki (1973), peninsula, and one may seek correlated Longhurst ( 1 998), etc.) but they need be treated differences in faunas. The most striking only superficially here, as most of their effects differences between these two bodies, namely on faunal composition are not yet clear. salinity and upwelling, will be briefly The influence of seasonally-reversing considered. monsoon gyres helps to explain the low endemicity and high percentage of pan-Indo- SaliniQ West Pacific elements, as this would facilitate The Bay of Bengal receives freshwater runoff incursion from both Malesia and the western (heaviest in autumn) from major river deltas Indian Ocean. For example, the offshore situated in the northern part of the Bay, islands of the Lakshadweep (Laccadive) and parlicularly the Ganges and Brahmaputra, and Maldive Archipelagoes - which are under the in Myanmar (Burma), the lrrawaddy. Surface more direct influence of the monsoon currents salinity is thus lower than in the rest of the - have a typical core lndo-Pacific molluscan northem Indian Ocean, mean salinitybeing in fauna (Surya Rao & Subba Rao (1991), and the order of 33-34%o, although southward flow Smith (1903)), with extremely few if any along the east coast India may reduce endemics. Howeveq as already discussed, the nearshore salinity to as low as 18 %o (La Fond discernible Western Indian Ocean influence 1966), at least as far south as the Andhra coast. appears minor; a specific example is the Furlhermore, even off the Tamil Nadu coast, Phuket Marine Biological Center Special Publication 26: 5-17 (2002)

which lacks major river systems, heavy winter been one factor in specific extinctions (Hallock rainfall may lower surface salinity to 25%o 1 987). (Pillai r97I). Bay of Bengal: Here, upwelling - and its An indirect result of the reduced salinity of effects - is not a major factor. Off the norlh surface waters is greatly impoverished coast, freshwater inflow from the major rivers plankton. As a consequence, the shelfbenthos is sufficient to inhibit upwelling locally. of the Bay of Bengal appears also to be Elsewhere along the east coast of India, weak generally much poorer than in the Arabian Sea. upwelling may follow favorable winds, In fact, in places a mean benthic biomass of parlicularly south of Visakhatapan (17.5"N). only 5.32 g/m2 is recorded (Dwivedi 1993), However, during the SW monsoon, upwelling against an average of up to 35 glm2 for the is suppressed by warm, low salinity surface northem Arabian Sea Q'{eyman et al. 1973). water (Johns et al.1992) (Of course, near the main deltas biomass may Arabian Sea: During summer, the SW be locally very high as a result of direct organic monsoons force strong wind-driven upwelling enrichment from rivers and mangrove along the southArabian coast; as a result, cold swamps.) water (temperature as low as 16 "C) rises to The Arabian Sea receives no major rivers the surface. At this time there is also wind- other than the Indus, so that only during the driven upwelling on the south-west coast of rainy season does the salinity of the upper 50 India (Backus 1994). The possible effects will m ever drop lower than 35 o/oo, and at other be noted 1ater. However, the organic times it may exceed 36 %o. Contributory enrichment resulting from upwelling may factors are high rates of evaporation in the result in unusually high benthic biomass; off central and nofthem Arabian Sea, plus inflow the northem coast of the Arabian Sea this may of hypersaline water from the Red Sea and exceed 500 glm2,the highest recorded for the Arabian Gulf. Indian Ocean during the International Indian In effect the Arabian Sea forms an Ocean Expedition (Neyman et al. 1973). evaporation basin, whereas the Bay of Bengal Furthermore, high evaporation in the central is a dilution basin - this will certainly have part of theArabian Sea results in denser surface some effect on their respective biotic water, which sinks, carrying oxygen down to compositions. One would expect, for example, moderate depths. a higher proportion of stenohaline taxa in the former area. This, however, remains to be (3) Baniers and filter-routes investigated. Biogeographic regions can only be differentiated where there exists some form of Upwelling boundary to reduce incursion of adjacent Upwelling plays a positive role in bringing faunas and facilitate vicariance. To quote nutrients to the surface, but by suddenly Pielou (197 9) : "boundaries of biotic provinces lowering surface temperatures may disrupt are determined by modern abiotic factors". development and reproductive cycles, and True barriers, such as land masses or even cause mass mortality, particularly when permanently adverse currents do not presently the upwelled water is low in oxygen and high exist within the Indian region, but there are in sulphides. Indeed, eutrophication resulting many filter-routes, which would impede from increased upwelling is believed to have dispersal (but do not prevent it), at least over 10 Tropical Marine Mollusc Programme (TMMP)

dispersed around its head. During glacial the passage of geological time. These are first maxima some continental shelf would remain possible effects are briefly outlined before accessible (the shelf break lies mostly in 120- discussed. 180 m, maximum lowstand was ca 120 m). During interglacials and other predominantly Bay of Bengal wet periods, flooding of low-lying coastal The hyposaline and turbid conditions that areas would have provided refugial lagoons seasonally exist in the northern parl of the Bay, and backwaters. However, even during the at least during wet phases, have presumably Eemian (or near its end) a cool, dry event has influenced incursion and vicariance, reducing been reported (see Adams 2000). During such the former and strengthening the latter, dry periods, reduction in inflow of freshwater certainly in the case of stenohaline littoral and and silt would have facilitated dispersal of shelf species. Climatic oscillations throughout sand-dwelling species across the head of the the Quatemary caused alternation of wet and Bay. dry phases; thus monsoon runoff was greater An example of a mollusc with intracapsular at the starl of the Holocene than todav (Cullen (crawl-away) development that has crossed the 1eB 1). Bay of Bengal and vicariated (see Kilburn Most Indian molluscs appear to have 1981) is the common Indian Ancilla ampla planktonic larvae, which would facilitate (Gmelin, I79f) (Fig. 6). The nominate dispersal, except perhaps during wet phases subspecies is somewhat euryhaline (mean when veligers must traverse surface waters that salinity within range 25-36.5 %o) and is are low in salinity and sometimes poor in distributed from Aden to Burma. However, it oxygen. However, for molluscs that hatch at is represented from the Andaman Sea the crawling stage, the Bay of Bengal could eastwards into Malesia by a distinct present a wide, deep-sea barier, as the narrow subspecies, Ancilla ampla cylindrica shelf slopes steeply from the shelf-break (at (Sowerby, 1859). Since its original dispersal, 120-180 m) to a depth of 3,000 m in the middle the Bay has evidently been restored as a banier, of the Bay and 4,000 m at entrance. Thus there leading to vicariance. can be no question of ancient shoals or An even more striking case is the genus "stepping stones" (apart from the Tertiary Turbinella, to which belongs India's Andaman Ridge of which the Andaman and characteristic "sacred chank", Turbinella Nicobar Islands are a remnant). Fufthermore, pyrum (Linnaeus, 1758) (Fig. 7). Its ancestry even at moderate depths ( I 00 m), temperatures has been traced to the widespread Tethyan Z drop to 12-18 oC, and below 300 m the water episoma (Michelotti, 1861), whose presence becomes oxygen-poor. Thus in effect the Bay in westem India dates from the Oligocene, and of Bengal is rimmed by a curved linear shelf which evolved into a sequence of species (sensuYalentine & Jablonski 1983) rather than which culminated during the Pliocene in the a two-dimensional one; the exception is the surviving Turbinella pyrum. fAlthough Gulf of Mannar/Palk Strait area, which now Vredenberg (1916 and 1923) was convinced (and during previous warm periods) is thatpyrum was not paft of the episomalineage rendered two-dimensional by the proximity of but an incursive from elsewhere, he did not Sri Lanka and many small islands. take into consideration possible character However, even species with crawl-away reversals, nor the extreme genetic diversity and young have traversed the Bay or at least phenotypic plasticity of T. pyrum (Hornell Phuket Marine Biological Center Special Publicstion 26: 5-77 Q002) 11

REGIONAL VARIATION (1916) documented a wide array of local races WITHIN INDIA and ecomorphs, several of which are In view of the oceanographic contrasts sometimes considered fuI1 species).] However, between the two coasts of lndia we would in theAndaman Islands and westem lndonesia expect some differences in faunal composition. occurs a second species, T. fu,stts Sowerby, To determine whether the region can be 1825, which according to Vredenberg appears subdivided faunistically one should ideally to be morphologically indistinguishable from start with exhaustive molluscan inventories, the ancestral T. episoma and can probably be which can be analyzed for patterns such as assumed to be a relict population, isolated by main centres of endemicity and position of the Bay ofBengal perhaps since the Oligocene. subtraction margins. Unfortunately, faunal lists The possible function of the Gulf of Manaar for India are mostly inadequate or have been as a banier during periods of low sea level is compiled by so many different authorities that touched on below. they cannot be directly compared with any confidence. The following thoughts are thus only tentative: Arabian Sea Three potential dispersal filters characterize the west coast of India. Firstly, as has been (1) The Delta Coast noted, seasonal upwelling of cold or oxygen- Much of Orissa, West Bengal and Bangladesh poor water is a characteristic of different parts comprise an estuarine coast, rich in mangroves, of the Arabian Sea. Similar effects are with a high outflow of freshwater and silt. Off produced by winter shoaling of the the Ganges delta, the continental shelf is ca thermocline, when barometric events on the 160 km wide, nanowing fuither south offthe west coast India and off Pakistan may cause predominantly sandy coast of Orissa to only the 20'C isotherm, low in oxygen, to rise to 40-120 km wide. Off Bangladesh salinities of o/oo less than 50 m (Wyrlki 1973). An oligotrophic 30-31 occur even during the dry season, area with a poor fauna of mainly suspension dropping to 17-18 %o during the rainy season feeders, is reported in 75-150 m; this partly (Dwividi 1993). The delta coast is naturally results from the frequent inflow of such characterised by many estuarine/backwater oxygen-poor water (Neyman et al. 1973). elements, including endemic bivalves such as Secondly, the presence of a mobile mud the pharids Tanysiphon rivalis Benson, 1858 bottom along parls of the Mumbai Shelf does (Fig. 8), and Novaculina gangetica Benson. not support a rich shelf biomass, which 1830 (Subba Rao e/ al. 1992). decreases to 5 gm/m2 down the west coast Slightly further south, on the Orissa coast. (Neyman et al. 1913). An associated about 1 I % of the modified total of 293 species phenomenon is the movement of inshore given by Subba Fiao et al. ( 1 99 1 ) are endemic, mudbanks ("chankara") on the inner shelf off although if backwater (brackish to freshwater) Kerala (Longhurst 1998). species are omitted, this would fallto 7 yo. Finally, off the Gulf of Kutch is a "dynamic The low salinity that has prevailed in the barrier", discussed by Nair (1984), which nofthem Bay of Bengal, at least during wet deprives the shelf of sediment, and will phases, has apparently facilitated the certainly negatively affect larval dispersal adaptation of a number of species of norrnally across the Indus region. marine groups to the brackish and freshwater t2 Tropic:al Marine Mollusc progr.anune CMMp)

refugia provided by the extensive estuarics and backwaters, the latter usually originating from the deposition of sand spits across the mouth of inlets. Examples include 3-4 species of Arcidae (genus Scaphula (Fig. a)), 2-3 af (subgenus Pvgmaeonassa of Nassarius (Figs. 9, 10)), and at least two Solenidae (lveosolen aclttaedttlcioris Ghosh,

1 9 I 6 (Fig. 5), and Solen annandalei Preston, 1915). The Orissa coast is particularly rich in endemic backwater molluscs - over 20 such species inhabit the Chilka Lake system and other backwaters (Subba Rao et al. 1991, 1995). In the Chilka Lake salinity originally fluctuated from 0.1 to 36 %0, being largely flushed out by freshwater during the rainy season except in the southern parl (Annandale & Kemp (1915, 1916), Annandale (1924), W Directorate of Fisheries (1970)). However, conditions have deteriorated considerably in recent years (see Conservation section). :to (2) South-East India (lhe Mannar-Palk Bay-Sri LcLnka area) This area is inhabited by India's best-known endemic molluscs, such as the Turbinella pyrum-species complex, Tudicla spirillus (Linnaeus, 1758) (Fig. l), Ancilla cinnamomea Lamarck, 1 801 (Fig. I 1), Semicassts canalictLlaturu (Bruguiere, 1792) (Fig. 12), Strombus klineoruun Abbott, 1960 (Fig. 13), zeylanica (Bruguiere, 1789) (Fig. 14), Harpulina lapponica (Linnaeus, 1758) (Fig l), Calliostoma tranquebaricum (Roding, 1798) (Fig. 15'), Turris variegata (Kiener, 1840,non Philippi, 1836), andBullia vittata (Linnaeus, 1767) (Fig. 16). The range of many of these elements extends north at least to Chennai (Madras) and eastward along 6 Ancilla atnpla the Sri Lankan coast. 7 Turbine]la pyrLnn It is unlikely to be coincidence that such 8 Tanysiphon rit'alis endemicity should be centered around anarea 9 Nassarius subconslrrcfus bounded in the norlh by a hyposaline filter t0 Na.ssarius orissa ensls route, and in the south by the Gulf of Mannar 1a Plruket Marine Biological Center Special Publicntiorr 25: 5-17 (2002) 1J

which formost ofthe Pleistocene (pers. comm. Dr P. Ramsay) would have formed at least a partial land bridge (the Paik Straits have a sill :t.i:ti:! depth of only 10 m). In other words, it is not unreasonable to speculate that the origin of this fauna may be traced to periods of low sea level, when the moiluscan fauna of what is now Paik Bay would have been largely isolated from the south coast fauna. Dispersal round the south coast of Sri Lanka would have been hindered by its narrow shelf and extremely steep continental slope, which descends at an angle of45o (La Fond 1966). To return to the Recent fauna, the presence of a relatively wide, two-dimensional shelf between India and Sri Lanka, with comparatively little fluctuation in salinity and temperature, now provides a refuge for a highly diverse fauna ofover 600 species. The area is relatively sheltered, at least during the NE monsoon, when a surface cuffent is forced south through Palk Strait. Temperatures are warm (28-30 'C) throughout the year in the shallows (UNEP/IUCN, 1988), although in the deeper channels these drop rapidly below 1 00 m, with temperatures as low as 13.5-18.0'C being recorded at 200 m (Sewell 1938). The Gulf of Mannar itself contains a chain of over 20 coral islands and many reefs, all shallower than 6 m. In the shallows are extensive grassbeds comprising some 13 species of marine angiosperms, which harbor Indian endemic molluscs such as Turris amicta (F,. A. Smith, 1877) and Fusinus laticostatus (Deshayes, 1831) plus some local endemics such as Colina selecta (Melvill & Standen, I B9B). On water characteristics, Colborn (1974) 11 Ancilla cinnamomea included the Gulf of Mannar in his "Laccadive 1 2 Senricassis cana liculatunl Sea", which extends up the west coast to south i i Srlorribri.r- k l i n c oru m Mumbai. remains demonstrated of It to | 4 B ab 1,|oni a zc,v lani c a whether the core south-east Indian fauna | 5 Cal/iostornt a t rtnquebaricuut extends far up the exposed Malabar coast. 16 vittata 14 Tropical Marine Mollusc Programme (TMMP)

(3) North-West India. This area has the widest shelf in India (reaching 400 km off the Gulf of Khambat, although extending only ca 70 km off the Indus), but narrows considerably to the south. The substratum consists mainly of sand, overlain by mud or clay, and turbidity is much higher than in the open Arabian Sea. Little has been published on the molluscs of north-westem lndia, although records from Mumbai (Bombay) were summarized by Subrahmanyam et al. (1949, 195I, 1952). These lists (obviously very incomplete and based mainly on early records by Melvill & Standen (1901)) indicate low diversity, totalling ca 310 species (excluding obvious misidentifications, freshwater and pelagic elements, etc.). Only a few typically Arabian Gulf elements are included, such as Drupa l: Consequently this claim is not here accepted. Ocinebrinaf xuthedra (Melvill, 1893) and Nevertheless, the scant evidence available Fusinus townsendi (Melvill, 1899) (Fig. 17). indicates that most of the west coast is However taken at face value the majority of occupied by a wide, somewhat depauperate shallow water molluscs are core lndo- subtraction margin of the south-east Indian Polynesian species, the few that are more coast (overlapped to an unknown extent by characteristic of South-East India, such as elements of the Arabian fauna). This could be Conus monile Linnaeus. 1758. and Turbinella ascribed to a combination of unfavorable pyrum (Linnaeus, 1758) (Fig. 7), being factors (discussed above) in various areas and ornamental shells that are widelv transported different seasons, notably the upwelling or by human agency. shoaling of cold, oxygen-poor water and an unstable mud bottom. To this may be added (4) South-West India the sandy (and frequently high-energy shore) In one of the very few definite statements of much of southerl Kerala, whose limited perlaining to the molluscan biogeography of hard substrates appear to harbour few molluscs India that have been published, Neyman et a/ except for the littorinid Nodilittorina (1973) claimed that Panjim (Nova Goa) was leucosticta (Philippi, I847) and the mytilid the boundary between eastern and western Perna indica Kuriakose & Nair, 1970 (an Indian molluscs, as this was "the northemmost apparent south-west Indian endemic, which is limit of the penetration of equatorial waters replaced in northern Tamil Nadu by the onto the shelf of western India". However, the Malesian P. viridis (Linnaeus, 1758)). latter statement was evidently based solely on The extent of endemicity amongst the oceanographic sampling conducted during one molluscs of the west coast littoral and shelf is month of one year, and no faunistic evidence unknown. However the presence of one marine is presented to justify their conclusion. group that has here adapted to freshwater Phuket Marine Biological Center Special Publication 26: 5-17 (2002) 15

should be noted; this is the endemic littorinid villages which daily drag nets over the genus Cremnoconchus (Fig. 3), two species neighbouring shallows. Fishing is not of which occur in the hill streams. selective and the bycatch, rich in molluscs, unwanted crustaceans and other benthos, is CONSERVATION either dumped on the shore to decompose or porl processed As indicated above, within the Indian region taken back to and as "trashfish", there are two main areas of molluscan apart from the more orrramental shells and endemicity, namely the backwater and starfish that are sold to dealers. The long-term prognosis estuarine systems of Orissa and the northem for the Gulf of Mannar benthos is good, coast of the Bay of Bengal, and the Gulf of not unless conservation ethics are introduced to the Mannarto Chennai area. Clearly, conservation fishing industry and strictly of these faunas is imperative, and on paper enforced by regulation. It is to be hoped that Palk Bay remain a reserrroir for this attempts have been made to address this need. will fauna. Thus Chilka Lake was designated as a RAMSAR site in 1981, and much of the ACKNOWLEDGEMENTS second region falls within the Gulf of Mannar This paper is based on a keynote address Marine Biosphere Reserve, established in delivered by me at the lltr' International 1 989. Congress of the Tropical Marine Mollusc Unfortunately, Chilka Lake is not only Programme in Kodaikanal lndia, in September shrinking at an estimated rate of 1 sq. km per 2000. I express my appreciation to Professor year as a result of progressive silting, but Jorgen Hylleberg, director of the programme, blocking ofthe outer channel has led to falling for the opportunity to participate in this and salinity, which threatens the survival of its other congresses and workshops of the TMMP. brackish-water molluscs. Pollution from I thank Dr J. K. Patterson Edward for his human habitations and prawn farms has hospitality and for facilitating fieldwork. I contributed to its degradation (Siddiqui & would also like to thank Dr N. Subba Rao for Rama Rao 1995). Significantly, Subba Rao e/ his hospitality during an early (1994) visit to al. (1995) reported collecting only 15 of the the Zoological Survey of India. 60 molluscan species described from the Lake. It is to be hoped that the announcement of REFERENCES designs to open a new outlet plus a Annandale, N. 1924. Fauna of Chilka Lake. "comprehensive catchment treatment plan" Moilusca, (Revision). - Memoirs of (The Times of India,lgth June 2000) will lead the Indian Museum 5: 853-873. to some reversal of this scenario. Annandale, N. & S.W.Kemp, 1915. Fauna of The Gulf ofMannarremains among the most Chiika Lake. Introduction. - Memoirs of the heavily exploited marine areas in India. From Indian Museum 5: 1-20. recent personal observations not only is the Annandale, N. & S.W.Kemp, 1916. Fauna of destruction of coral reefs ("coral mining") Chilka Lake. Mollusca, Gastropoda and Lamellibranchia. - Memoirs of the Indian ubiquitous and blatant, but there is no control Museum 5:328-314 over the activities of the more than 50,000 Bakus, G.I. et al 1994. Coral Ree/'Ecosystems. fishermen exploiting the region. Large fishing Rotterdam: Balkema. fleets trawl the deeper grounds with fine-mesh Briggs, J.C. 1914. Marine Zoogeography. New nets, and the mainland is lined with fishins York: McGraw-Hill Book Co. IO T'opical Marine Mollusc Progranme (TMMP)

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