Vertical Distribution of Molluscs in the Intertidal Area in and Around
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Journal of the Indian· Fisheries Association 93 28, 2001, 93-100 VERTICAL DISTRffiUTION OF MOLLUSCS IN THE INTERTIDAL AREA IN AND AROUND MUMBAI, INDIA. A. K. JAISWAR AND B. G. KULKARNI* Central Institute of Fisheries Education (Deemed University) Seven Bungalows, Mumbai- 400 061. India. ABSTRACT Vertical distribution of intertidal molluscs in and around Mumbai had been studied. Each species has an upper and lower limit of distribution along the vertical intertidal gradient and are concentrated at particular levels or zones where they find optimum living conditions. Zonation of the intertidal area with reference to molluscs at rocky shores of TIFR, Bandstand and NCPA have similarities. However, there is no similarity in zonation among rocky, sandy and muddy shores. Rocky intertidal zones are more diverse and dense in terms of molluscs. The mid and lower littoral zones have rich molluscan diversity. The upper littoral zone at some sites, especially Girgaon chowpatty is totally devoid of molluscs due to anthropogenic activities. Gafrarium divaricatum, Nerita oryzarum, N. polita and Neritina crepidularia have established themselves in all three marked zones, indicating their power to adjust with the wide fluctuations in surrounding environmental conditions. Keywords : Interidal, molluscs, zonation, pollution, dominance. INTRODUCTION 1933). Species at high shore levels have appropriate morphology, physiology and The intertidal region, a zone of behaviour to allow them to survive for longer interaction between sea, land and periods without being submerged in sea atmosphere, is one of the most interesting water, whereas species of lower level are divisions of marine ecosystem, as it is daily essentially marine and can cope only for covered and uncovered by flooding and brief period of exposure. Each species has ebbing tides. The width of intertidal belt an upper and lower limit of distribution exposed depends on the level of high and along the vertical intertidal gradient of low tides and gradient of the shore. The shore and are concentrated at particular inhabitants of this zone are known to be levels or zones where they find optimum hardy and highly diverse as the result of living conditions. These zones are usually diel changes in exposure, dessication and named after their dominance. The most submergence. This area ranks next only to outstanding contribution in the field of the sub-tidal region in terms of richness zonation is that of Prof. and Mrs. and variety of the life it supports (Colman, Stephenson, who, after 30 years of research * The Institute of Science, 15 Madam Cama Road, Mumbai - 400 032. India. 94 JAISWAR AND KULKARNI in the field, put forward an universal system near TIFR (Tata Institute of Fundamental of interidal zonation in 1949 (Stephenson Research) at Colaba represents, the and Stephenson, 1949). Zonation of species southern most end ofMumbai Island. The in intertidal area has been studied by many shore is an open type and hence subjected workers in different countries (Evans, 1948- to direct wave action throughout the year. Great Britain; Stephenson and Stephenson, In order to protect the shore line from 1949-Australia; Chapman and Traverthen, erosion due to wave action cement boulders 1953-New Zealand; Southward and Oston, are arranged along the upper most zone of 1954-Australia; Arudpragasum, 1970- the shore. Remaining intertidal area is Srilanka; Lubchenco, 1980. England and formed of rocks and boulders of varying Rakocinski et al., 1993-USA) dimensions. Maximum width of intertidal belt recorded during spring low tides Though India is surrounded by sea (0.03m) is 315m and shore exhibits very from three sides, with a long coast line of uneven profile. This shore is protected and 8129 km, very limited studies have been prohibited therefore, it is free from human done on intertidal zonation, such as those activities. As a result, it is cleaner than of Bhatt (1959), Parulekar (1973), Balani other stretches ofMumbai shore. (1975) and Sriramamurthy (1980). ii) NCPA shore : NCPA (National One of the most dominant group of Center for Performing Art) sea shore is a animals occupying the intertidal zone are semi-sheltered shore. Big cement boulders molluscs. The molluscs are not only rich and stones are arranged in the high water protein source for the people, but also play zone in order to avoid erosion of the shore. a very important role in small scale The remaining part of the shore is comprised industries as molluscan shells are used in of stones and debries like bricks and preparation of washing soda, cement, lime, concrete structures. Initially, it was a sandy jewelleries, decorative items and various shore but today it is neither a rocky nor a medicines. The economic importance of the sandy shore. However, it is much similar molluscs compelled us for recording the to rocky shore. The shore has a very steep vertical distribution of mollscan species slope, therefore, shore are exposed during inhabiting in the intertidal zone in and spring low tide (0.06m) is limited to 31m around Mumbai. only. iii) Girgaon shore : This shore is MATERIAL AND METHODS located in south Mumbai and popularly known as Girgaon Chowpatty. It is a sandy TOPOGRAPHY OF SELECTED SITES: shore and one of the most famous Mter a preliminary survey of entire recreational points for people living in coastline around Mumbai, the following Mumbai. Thus thousands of people visit sites (Fig. 1) were selected for the present the shore every day, as a result of which study. the ecological conditions of the shore are deteriorated. It is a very gently sloping i) TIFR Shore : The coastal stretch shore and therefore, a large width (58 1m) VERTICAL DISTRIBUTION OF MOLLUSCS IN THE INTERTIDAL AREA 95 IN AND AROUND MUMBAI, INDIA 7t30' BASSEIN ~ A C~EEK R A 19d 8 15' l v A N s E • A IV .. 19- 19 N ili ii .. 65 Fig. 1: Map showing sites ofinvestigation i) TIFR shore ii) NCPA shore iii) Girgaon shore iv) Bandstand shore v) Gorai creek 96 JAISWAR AND KULKARNI of shore is exposed during spring low tide The distribution pattern of molluscs in (0.06m). these zones at each station was studied on fortnightly basis between September 1996 iv) Bandstand shore : It is situated and August 1998. Molluscs were identified at Bandra, the mid point of western coast following Hormell (1949); Subrarnanium et line ofMumbai. It is an open type of natural al., (1949, 1951, 1952); Bhatt (1959); Rao rocky shore composed of rock beds and (1982) andApte (1996). Identities of some of stones of various dimension. It is also the specimen were confirmed by ZSI, subjected to direct wave action throughout Kolkata. the year. Maximum exposure was recorded 198m during spring low tide (0.03m). Shore profile is very uneven. RESuLTS AND DISCUSSION v) Gorai Creelt : Gorai creek is Zonation of molluscan species at situated at the northern end of Mumbai, NCPAshore: · which has a narrow link with Arabian Sea. Many narrow and wide drainage channels The upper littoral zone measurmg discharge their effluents into it. The creek 11.5m, was dominated by Littorina encloses a large area of mud flat infested intermedia, L. ventricosa and Tectarius with dense mangrove on both sides, which malaccanus, hence this zone is known as gets competely exposed during low tide the littorinid zone. Of the three littorinids measuring 96m in width (0.03m). T. malaccanus was most dominant species found crawling up to 1m above the mark of Total width oftidal belt exposed during spring high tide (splash zone). L. ventricosa spring low tide, and shore profile at the was not found in certain months of the selected sites were measured following Bhatt year. In the lower level of upper littoral (1959) and Holme and Mcintyre (1971). zone sporadic distribution of gastropods Following Bhatt, (1959) and Parulekar Drupa contracta, D. subnodulosa, Thais (1973) three tidal zones were adapted for tissoti, Nerita oryzarum andN polita were regular study. recorded. 1. Upper littoral zone (High water Although the narrowest (9.0m) of the zone - HWZ) - area between highest high three zones, the mid littoral zone ofNCPA water (spring tide) mark and lowest high shore had a rich molluscan diversity. water (neap high tide) mark. Gastropod species Nerita oryzarum, N. 2. Mid littoral zone (Mid water zone polita, Drupa contracta, D. subnodulosa, MWZ) - area between lowest high water D. konkanensia, Planaxis sulcatus, Bursa mark and highest low water (neap low tide) tuberculata, B. granularis, Thais mark. carinifera, T. tissoti, Pyrene terpsichore , Cypraea arabica, Hemifusus pugilinus, 3. Lower littoral zone (Low water zone Cellana radiata and bivalve species Area - L WZ) - area between highest low water symmetrica, Gafrarium divaricatum, mark and lowest low water (spring low Anomia achaeus, Crassostrea gryphoides tide) mark. VERTICAL DISTRIBUTION OF MOLLUSCS IN THE INTERTIDAL AREA 97 IN AND AROUND MUMBAI, INDIA and C. lugubris were found in this zone. A. Gastropods Nerita polita, N.oryzarum, acheus and Crassostrea gryphoides were N.albicilla, Planaxis sulcatus, P. simils, very common, but C. lugabris was recorded Cerithium morus, Ergaea walshi, Thais only twice. Gastropods Cypraea arabica, blanfordi, T. tissoti, T. carinifera, Cypraea and Drupa kokanensis were recorded only arabica, Bursa tuberculata, Drupa twice during the study. H. pugilinus was contracta, D. tuberculata and D. recorded occasionally, however, P. sulcatus knokanensis were collected in the mid and Drupa contracta were most dominant. littoral zone at both shores, However Conus textile, C. piperatus, Murex adustus, Aplsia Lower littoral zone covers a width of benedicti were noticed at TIFR and T. 12.5m of the shore thereby representing rudolphi. T. hippocastanum, Pyrene the widest part of this shore. The trochids terpsichore, P. atrata were found Euchelus indicus, E.asper, Trochus exclusively at Bandstand shore. Highest radiatus, Clanculus depictus, C. ceylanicus density of P. sulcatus and P. atrata were and C.