TAPROBANICA , ISSN 1800-427X. April, 2011. Vol. 03, No. 01: pp. 18-30. © Taprobanica Private Limited, Jl. Kuricang 18 Gd.9 No.47, Ciputat 15412, Tangerang, Indonesia. BENTHIC MACRO-INVERTEBRATE FAUNA AND “MARINE ELEMENTS” SENSU ANNANDALE (1922) HIGHLIGHT THE VALUABLE DOLPHIN HABITAT OF RIVER GANGA IN BIHAR - INDIA Sectional Editor: Remadevi Submitted: 28 February 2011, Accepted: 13 July 2011 Hasko Nesemann1, Gopal Sharma2 and Ravindra K. Sinha1 1 Centre for Environmental Science, Central University of Bihar, BIT Campus, Patna–800 014, India 2 Zoological Survey of India, Gangetic Plains Regional Centre, Road No. 11-D, Rajendra Nagar, Patna–800 016, India E-mail: [email protected] Abstract From the main channel of River Ganga 95 invertebrate taxa have been recorded in the endangered Gangetic Dolphin (Platanista gangetica) habitat over an observation period of ten years. Mollusks, Annelids and Arthropods are the dominating benthic groups that constitute the detritivores, filter-feeders and sediment feeders, scrapers/grazers and herbivores. The benthic sediment fauna is rich in diversity and high in abundance. This enables carnivores to occupy a large variety of specialized ecological niches. The qualitative faunal composition of Ganga resembles in general large European rivers with similar representation of taxa. Twelve taxa of marine-originated families were identified, but none of them can be classified as invasive or non-indigenous species. Only two taxa are certainly recognized as non-indigenous neozoans, whereas the remaining fauna shows pristine and stable ecological conditions. In this aspect River Ganga differs from regulated large rivers, where faunal change has largely replaced the original species inventory. Despite the heavy pollution in parts of the river, the original composition of biological diversity is still persisting in the middle reaches of the Ganga. This provides hope for the survival of the Gangetic Dolphin. Key words: Aquatic, invasive species, functional feeding groups, Gangetic Dolphin Introduction The Ganga is the largest river among the rivers It is a water resource for one of the world’s most originating from the Himalayan region in northern fertile plains with pristine river morphology. This India. The river section in Bihar is one of the few river is an irreplaceable unique habitat for the natural and free-flowing large rivers in south Asia. endangered Gangetic dolphin, Platanista gangetica 18 TAPROBANICA VOL. 03: NO. 01 BENTHIC MACRO-INVERTEBRATE FAUNA & “MARINE ELEMENTS” OF RIVER GANGA - INDIA gangetica (Roxburgh 1801) and many other visited frequently and their exact results are shown endemic and endangered species. in table 1-3. In addition the left (sedimentation-) bank opposite city of Patna was visited between The benthic fauna studied included all groups of October and March for collecting faunal samples taxonomic units to provide comparable results from different habitats (Boulders, sand, silt and regarding diversity of different habitat-types. mud substrate). Reference data were available for several invertebrate groups only through Datta Munshi et Results al. (1988), Sharan & Sinha (1988), Sinha (1988) The benthic macro-invertebrate fauna of the main and Subba Rao (1989) from the localities near channel comprises 95 identified taxa with high Patna. Systematic investigations have been diversity of 26 species of annelids (Table 1), 35 conducted for several gastropods e.g. Stenothyridae species of mollusks (Table 2) and 29 families, and Physidae (Sinha & Sharma 2001; Sinha et al., genera or species of arthropods (Table 3), The 2003), bivalves (Nesemann et al., 2003, Nesemann higher crustacean (Malacostraca) fauna includes 8 et al., 2005) and Annelids (Nesemann et al., 2004). taxa of crabs, prawns, shrimps, mysid shrimps and one isopod. Aquatic insects are mainly represented Although throughout most of its range the Gangetic with 21 identified taxa out of which nymphs of dolphin is declining because of river developments, Dragonflies and Damselflies, larvae of Two-winged pollution, deliberate killing and entanglement in flies and adults of Water-Bugs are the most striking nets (Smith and Braulik, 2008) all along the study groups. Additionally the presence of Roundworms area there is a good habitat. Five to ten dolphins (Nematoda) and Ribbon worms (Nemertina) was were regularly surfacing a few meters away from generally noticed with small abundances. the sampling sites in the main current. Altogether up to 37 dolphins inhabit the River Ganga stretch Functional Feeding Groups of Macro- around Patna (Sinha et al., 2010). invertebrates in the River Ganga: The habitat was classified according to longitudinal and lateral Materials and Methods terminology described and defined by Illies (1961), The macro-invertebrate fauna of the Ganga River Illies & Botosaneanu (1963) and Amoros & Roux was investigated frequently along the right bank in (1988). The River Ganga at Patna is a heterotrophic the city of Patna. Benthic samples were collected Meta-Potamon system. Organic load is brought qualitatively using a hand net. Annelid specimens from upstream through river-continuum or it is were preserved in 70% ethanol; leeches were introduced from surroundings along the banks and usually relaxed in 15% ethanol, and then transferred during flood. According to the commonly used into 70% ethanol for preservation. Molluscs and classification of higher invertebrate taxa and field decapods were washed from the sediment samples observations, their particular role in processing food at the spot and if necessary preserved in 4% can be roughly outlined at least at family level. formaldehyde. Usually only empty shells of large Each taxon is assigned to a specific functional bivalves have been collected and living specimens feeding group based on the definitions of Vannote were released. et al. (1980), Williams & Feltmate (1992), Merritt & Cummins (1996). Functional feeding groups at Study area: The main study area is the right family level (Tables 1-3) are summarized and (erosion-) bank of a 4km stretch of River Ganga figured for 51 taxa found in River Ganga at Patna, along the city of Patna from Mahendrughat in the based on the qualitative composition of benthic west (25° 37’ 19” N, 85° 09’ 18” E) downstream to fauna (Fig. 1). Bhadraghat in the East (25° 36’ 40” N, 85° 12’ 35” E). The faunal collection were done from The detritivores include in part shredders Mahendrughat, seeping springs, Mahendrughat (Polychaeta) and scrapers or grazers (Gastropoda) downstream, Adalatghat, Periphyton, Krishnaghat with all sediment- and filter feeders. Altogether 54 upstream, Gandhighat, Old Palace, Lithal, artificial % of the families can be assigned to this group (Fig. stone substrate, Old Palace, Phytal: Potamogeton 2). The true carnivores represent 34 % of the crispus. qualitative faunal composition, indicating high diversification and prey specialization (Fig. 3). The research was conducted from 31st January 2000 Herbivores (minimum of 2 % or more) are the to 31st January 2011 including frequent field minor group in the turbid River Ganga, and this observations. Altogether eight sites have been may well reflect the rare occurrence of vascular 19 TAPROBANICA VOL. 03: NO. 01 NESEMANN ET AL., 2011 aquatic plants along the banks. Some scrapers the Delta” and “The Relict Fauna of the River”. He among the gastropods, especially Lymnaeidae, and listed three bivalves Novaculina gangetica, miners among the insects e.g. Pyralidae nymphs of Scaphula celox and Scaphula deltae as relict fauna. moths feed mainly on living algae and macrophytes. Their occurrence in River Ganga nowadays extends upstream to 1500 km away from coastal waters and the Gangetic delta region. According to Annandale (1922) they are possible marine relics of the former tertiary sea. Figure 1: Qualitative composition of Benthic Macro- Invertebrates of the River Ganga at Patna with 95 identified taxa. Figure 3: Functional Feeding Groups of Benthic Macro- invertebrates in River Ganga with 51 classified families of the present study. Presently a total of twelve species of the macro- invertebrates occur at Patna belonging to marine- originated or primary brackish water families. These are Nereididae: Namalycastis indica, Nephthydae: Nephthys oligobranchia, Ozobranchidae: Ozobranchus shipleyi, Stenothyridae: Stenothyra ornata, Gangetia miliacea, Arcidae: Scaphula celox, S. deltae, Psammobiidae: Novaculina gangetica, Mysidae: Gangemysis assimilis, Corallanidae: Tachaea spongillicola, and Hymenosomatidae: Hymenicoides carteri, Neorhynchoplax spp. Recent observations of invertebrate invasion along Figure 2: General Feeding Guilds of Benthic Macro- large rivers used as waterways allow two alternative Invertebrates in River Ganga with 51 classified families hypotheses: of the present study: Dominance of Detritivores (54 %), 1. The occurrence of the above-mentioned species Herbivores and others (12 %) over Carnivores (34 %). in freshwater upstream from the upper tidal limit are true marine “Relict fauna of the River Ganges” The “Marine Element” (Annandale 1922): according to Annandale (1922). Besides the Gangetic River dolphin Platanista 2. The occurrence of the above mentioned species gangetica gangetica, some unique freshwater in freshwater upstream from the upper tidal limit is species of predominantly or nearly exclusively based on both recent introduction by shipping and marine invertebrate families have drawn early ongoing upstream range extension by active attention