BENTHIC MACRO-INVERTEBRATE FAUNA AND “MARINE ELEMENTS” SENSU ANNANDALE (1922) HIGHLIGHT THE VALUABLE DOLPHIN HABITAT OF RIVER GANGA IN BIHAR - INDIA

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.


Introduction
The Ganga is the largest river among the rivers originating from the Himalayan region in northern India.The river section in Bihar is one of the few natural and free-flowing large rivers in south Asia.
It is a water resource for one of the world's most fertile plains with pristine river morphology.This river is an irreplaceable unique habitat for the endangered Gangetic dolphin, Platanista gangetica TAPROBANICA VOL.03: NO. 01 gangetica (Roxburgh 1801) and many other endemic and endangered species.
Although throughout most of its range the Gangetic dolphin is declining because of river developments, pollution, deliberate killing and entanglement in nets (Smith and Braulik, 2008) all along the study area there is a good habitat.Five to ten dolphins were regularly surfacing a few meters away from the sampling sites in the main current.Altogether up to 37 dolphins inhabit the River Ganga stretch around Patna (Sinha et al., 2010).

Materials and Methods
The macro-invertebrate fauna of the Ganga River was investigated frequently along the right bank in the city of Patna.Benthic samples were collected qualitatively using a hand net.Annelid specimens were preserved in 70% ethanol; leeches were usually relaxed in 15% ethanol, and then transferred into 70% ethanol for preservation.Molluscs and decapods were washed from the sediment samples at the spot and if necessary preserved in 4% formaldehyde.Usually only empty shells of large bivalves have been collected and living specimens were released.
The research was conducted from 31 st January 2000 to 31 st January 2011 including frequent field observations.Altogether eight sites have been visited frequently and their exact results are shown in table 1-3.In addition the left (sedimentation-) bank opposite city of Patna was visited between October and March for collecting faunal samples from different habitats (Boulders, sand, silt and mud substrate).

Results
The benthic macro-invertebrate fauna of the main channel comprises 95 identified taxa with high diversity of 26 species of annelids (Table 1), 35 species of mollusks (Table 2) and 29 families, genera or species of arthropods (Table 3), The higher crustacean (Malacostraca) fauna includes 8 taxa of crabs, prawns, shrimps, mysid shrimps and one isopod.Aquatic insects are mainly represented with 21 identified taxa out of which nymphs of Dragonflies and Damselflies, larvae of Two-winged flies and adults of Water-Bugs are the most striking groups.Additionally the presence of Roundworms (Nematoda) and Ribbon worms (Nemertina) was generally noticed with small abundances.

Functional
Feeding Groups of Macroinvertebrates in the River Ganga: The habitat was classified according to longitudinal and lateral terminology described and defined by Illies (1961), Illies & Botosaneanu (1963) and Amoros & Roux (1988).The River Ganga at Patna is a heterotrophic Meta-Potamon system.Organic load is brought from upstream through river-continuum or it is introduced from surroundings along the banks and during flood.According to the commonly used classification of higher invertebrate taxa and field observations, their particular role in processing food can be roughly outlined at least at family level.Each taxon is assigned to a specific functional feeding group based on the definitions of Vannote et al. (1980), Williams & Feltmate (1992), Merritt & Cummins (1996).Functional feeding groups at family level (Tables 1-3) are summarized and figured for 51 taxa found in River Ganga at Patna, based on the qualitative composition of benthic fauna (Fig. 1).
The detritivores include in part shredders (Polychaeta) and scrapers or grazers (Gastropoda) with all sediment-and filter feeders.Altogether 54 % of the families can be assigned to this group (Fig. 2).The true carnivores represent 34 % of the qualitative faunal composition, indicating high diversification and prey specialization (Fig. 3).Herbivores (minimum of 2 % or more) are the minor group in the turbid River Ganga, and this may well reflect the rare occurrence of vascular aquatic plants along the banks.Some scrapers among the gastropods, especially Lymnaeidae, and miners among the insects e.g.Pyralidae nymphs of moths feed mainly on living algae and macrophytes.

The "Marine Element" (Annandale 1922):
Besides the Gangetic River dolphin Platanista gangetica gangetica, some unique freshwater species of predominantly or nearly exclusively marine invertebrate families have drawn early attention of scientists.Annandale (1922) has already distinguished two groups of marine origin characterizing these as "The Euryhaline Fauna of the Delta" and "The Relict Fauna of the River".He listed three bivalves Novaculina gangetica, Scaphula celox and Scaphula deltae as relict fauna.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.

Recent observations of invertebrate invasion along large rivers used as waterways allow two alternative hypotheses:
1.The occurrence of the above-mentioned species in freshwater upstream from the upper tidal limit are true marine "Relict fauna of the River Ganges" according to Annandale (1922).2. The occurrence of the above mentioned species in freshwater upstream from the upper tidal limit is based on both recent introduction by shipping and ongoing upstream range extension by active dispersal as a response to the increasing human impact with environmental changes of habitat.
Since the species are restricted to the Ganges River, their presence may be due to the use of the waterway during the last one hundred years.On other hand, some species of "marine origin" are widespread throughout the Gangetic plain.Here the artificial introduction by shipping is most unlikely.All species are native to the Indian subcontinent, eleven of them being originally described from the delta region of River Ganges with type localities somewhere in Hugli River floodplain or connected channels.Two examples will be described here in detail with data of their first collections (Nesemann et al., 2007)  This isopod has been originally described by Stebbing (1907) from a freshwater tank at Kolkata as a commensal of the freshwater sponge Spongilla carteri.The first record of T. spongillicola being collected as ectoparasites of freshwater prawns Macrobrachium spp. in southern India was published by Mariappan, Balasundaram & Trilles (2003).During the present survey T. spongillicola was regularly collected from benthic samples of lowland streams and small rivers of the Lower Gangetic Plain in Nepal and India as well as from River Ganges itself.The wide distribution range exceeds northwards to the Himalayan foothill streams in the Terai region.This may indicate the natural pattern of dispersal.This mysid shrimp has been originally described by Tattersall (1908) from a brackish water pond at Port Canning.The first records of G. assimilis were collected in small rivers and oxbow lakes of southern Nepal from December 2005 onwards (Nesemann et al., 2007).During the present survey G. assimilis was collected from periphyton-samples from River Ganges itself in March 2008.The wide distribution range northwards to the Himalayan foothill streams in the Terai region resembles the distribution pattern of the isopod T. spongillicola.It supports the natural pattern of dispersal of this species.

How to identify invasive species (Neozoa) among benthic Macro-invertebrates in the River Ganga?
Neozoa are numerously reported among the aquatic invertebrates of many large rivers all over the northern hemisphere.The neozoa are benefited from regulated rivers and ships often initially distribute them.The total amount of non-indigenous macro-invertebrates in rivers can be used to understand and describe the degree of anthropogenic changes of the potamocoenosis environment.Many neozoa tolerate higher salinity as well and originate from costal brackish waters.Therefore several neozoa (e.g. the Danubian Limnomysis benedeni Czerniavsky, 1882 of the ponto-caspian basin) have been erroneously regarded as marine relicts.This question is of great interest for the River Ganga fauna.It makes it necessary to review thoroughly the following four aspects for each species: 1.How long back does the knowledge of any particular species dates? 2. From which country and watershed the species has been described?3. Is there any certain observation of the invasive character of the species?4. Does the analysis of the present-day distribution pattern allow any conclusions about the probable impact of transportation by waterways?
Many taxa of River Ganga that could be identified to species level are most likely a part of the indigenous fauna; based on the knowledge from their first observations.They could have been originally described from either northern Indian subcontinent or from Gangetic delta and certain literature records are known from nineteenth or early twentieth century.For some popular gastropods, the River Ganga is representing the "terra typica" without any precise location e.g.Brotia costula.Early observations of numerous aquatic molluscs have been already mentioned from Gangetic plains by Preston (1915) and Annandale (1922) and additional records were summarized by Subba Rao (1989).Several malacostracans (Mysida, Decapoda) have been originally described from Gangetic delta in Bengal.Similarly some of the wide spread oriental leeches have been already reported from at least few localities of Gangetic Plains by Harding & Moore (1927).Thus the presumed theory of recent faunal changes in River Ganga by invasion or introduction of euryhaline and pollution-tolerant neozoa is not supported with any certain observations.In contrast it has to be highlighted that all members of marine-originated families are autochthonous species of the river since their scientific discovery and description.
Among all invertebrates found in the study area at Patna only two species can be certainly identified as non-native invaders, so-called neozoa (Fig. 1).The gastropod Haitia mexicana is of nearctic origin with rapid spreading during last fifteen years.This North American Physidae Haitia mexicana was invading the river system since the early nineties, starting from few introductions in 1994 in capitals like New Delhi and Kathmandu and in 1998 in Allahabad.Its rapid spreading was initiated by commercial distribution of aquaria material and aquatic plants.
Shortly after colonization of River Ganga in Patna after 1998, H. mexicana was found in high abundance.Since that time the individual density is declining.Mass occurrence is nowadays restricted to few highly polluted places, where H. mexicana lives without competition with other gastropods (Sinha et al., 2003).
The earthworm Perionyx excavatus originates from the Eastern Himalayan foothills (Gates, 1972).This species is helpful in agriculture, with successful early introductions to subtropical countries all over the world.Many pan-tropical localities have been already reported by Gates (1972) from the first half of twentieth century.In Gangetic Plain P. excavatus appears to be well established since long.Thus the occurrence in semi-aquatic zone of River Ganga at Patna might be the result of natural invasion from agricultural terrestrial habitats.Kinzelbach (1983Kinzelbach ( , 1985)), Sopp (1983), Ziese (1985Ziese ( , 1987)), Schmid (1999) and Schleuter & Haybach (2003) provide benthic faunal particulars of the main river channels (Table 4).The available physico-chemical parameters show similar condition in the lowland rivers except of the temperature range.

Comparison of River Ganga fauna (Oriental region) with large rivers of temperate
In biodiversity all large rivers have three main components of benthic macro-invertebrates: Mollusca (Class: Bivalvia, Gastropda), Arthropoda (Class: Malacostraca, Insecta) and Annelida.Molluscs are more diversified and most dominating in River Ganga with 38 % of identified taxa.The temperate aquatic malacofauna ranges from 21 -28 %.Arthropods are leading groups in Rhein (Rhine), Main and Oder Rivers with 33 -51%, but identification level cannot be compared directly due to different species-, genus-and family-level.In contrast the Gangetic insects (23 %) are insufficiently known from the preliminary list at family level.In Annelids all three major groups (Polychaeta, Oligochaeta, Hirudinida) cover 28 % of the identified taxa in River Ganga and the fauna has been carefully investigated and described.The Neozoa in River Ganga compared with the European Rivers (Fig. 4): In regulated large rivers of temperate zone the indigenous or native benthic invertebrates are becoming accompanied by aquatic invaders or invasive species.They are partially replacing the reduced original fauna or even occupy free ecological niches.Neozoa play an important role in benthic fauna of navigable rivers.Their increasing number of species is sufficiently documented in some European rivers and especially studied for River Rhine (Fig. 4).The relative amount of non-indigenous invasive species changes from estimated 2 -6 % to approximately 12 -18 % of the total number of identified taxa within the last hundred years (Kinzelbach 1983, Nehring 2003).Similar tendency in Rivers Main (21 Neozoa) and Oder (14 Neozoa) is showing the same range.The quality of hard substrate in form of large natural boulders is providing stable surface habitat for lithophilic species, especially leeches (Hirudinida) and snails (Gastropoda) largely supported by the interspaces and subsurface.These artificially created micro-habitats are stable against flood-disturbance during monsoon period.
Lotic/rheophilic species are declining (Novaculina gangetica, Namalycastis indica, Hymenosomatidae), whereas lentic fauna is more supported by the residual flow with side-arm condition during low water period.Especially the increasing density and extension of large freshwater mussels is co related with the environmental changes.Dense mussel-beds were observed in May 2010 at Gandhighat, where ten years ago in January 2000 mostly Thiara scabra and Thiara lineata have been the dominating molluscs.Polychaetes and spider crabs disappeared at the same place.

Faunal change of benthic macro-invertebrates in
River Ganga: Compared with initial studies (Sharan andSinha 1988, Sinha 1988), the number of taxa is continually growing throughout the last years.In the following decades more detailed studies have been conducted and thorough sampling has brought to light the discovery of many species.On the other hand, the continuous fieldobservations have clearly documented some faunal change for several groups: The present scientific knowledge of macroinvertebrates from River Ganga before the twentieth century is very poor.It is limited mainly to collections of molluscs (Preston 1915, Annandale 1922).Many invertebrate species of marine and brackish origin were described in the early twentieth century and no exact observations prior to their scientific descriptions are available.Thus "The Relict Fauna of the River" (Annandale 1922: 146) "that flourish in the Middle Reaches of Ganges" cannot be certainly assigned to invasive, nonindigenous species.Considering the high number and native character of the marine-originated families, they can be regarded as original members of the eco-region of Lower Gangetic Plains.There is neither proof for their rapid invasion within the last decades, nor for their absence.The few studies on benthic fauna do not allow comparison of the present-day situation with former conditions one hundred years ago.While comparing River Ganga with regulated European rivers the presumed analogous faunal change is not supported.In contrast Ganges fauna has preserved comparatively semi-natural conditions with original species inventory of most invertebrates.The benthic neozoa are actually represented with 2 % of total identified taxa, similar to large European rivers at the end of nineteenth century (Fig. 4).Thus the River Ganga around Patna displays a rich aquatic biodiversity, but the ecological status needs sustainable conservation and improvement of the ecosystem.Widespread and locally abundant Family Dytiscidae Gen spp.
Fairly common Family Hydrophilidae Gen spp.

Figure 1 :
Figure 1: Qualitative composition of Benthic Macro-Invertebrates of the River Ganga at Patna with 95 identified taxa.

Figure 3 :
Figure 3: Functional Feeding Groups of Benthic Macroinvertebrates in River Ganga with 51 classified families of the present study.

Figure 4 :
Figure 4: Presence of Neozoa in River Ganga main channel in comparison with lowland-reaches of large river systems (main channels) in Central Europe, Germany.
European rivers display similar amount of annelid taxa with 30 % for Order, largely based on the very rich Tubificidae diversity, up to 19 % for Rhine and 17 % for Main River.It is noteworthy that the true freshwater Polychaeta were originally absent in the river systems of North and Baltic Sea.

Table 1 :
Taxa-list for Annelida in River Ganga at Patna.

Table 2 :
Taxa-list for Mollusca in River Ganga at Patna.

Table 4 :
Benthic Macro-Invertebrates of River Ganga main channel in comparison with lowland-reaches of large river systems (main channels) in Central Europe: