Faunal Diversity in India: Bryozoa
This is an extract from
FAUNAL DIVERSITY IN INDIA
J. R. B. Alfred
A. K. Das
A. K. Sanyal.
Zoological Survey of India,
( J. R. B. Alfred was
Director, Zoological Survey of India)
Bryozoa are sessile, lophophorate, aquatic, colonial, coelomate inverterbrates with a recurved digestive tract bringing the anus near, but outside the mouth. They have no special respiratory, circulatory or excretory organs. Colonies may comprise of a single feeding zooid or hundreds or thousands or even a million. The supporting exoskeleton may be cuticular, gelatinous or commonly calcareous. At various times, they were also called 'polyzoa' or 'Ectoprocta' in literature, but majority of present day bryozoologists accept the term Bryozoa.
Status Of The Taxon
Global and Indian Status
Although regarded traditionally as a minor phylum, the group contains as many as 20,000 described species actually occupying an intermediate position in the heirarchy of animal phylum in respect of species representation. Of these, approximately 4,000 species are extant (living). At least 200 valid species occur in Indian waters i.e., approximately 5% of the liVing species.
In India, as in other parts of the world, only a few species of bryozoans inhabit fresh water lakes and rivers (Phylactolaemates), but most are marine or estuarine. Greatest abundance of bryozoa is in the shallow waters. These are common interesting components of the rocky intertidal and have been reported from several localities along both the East and West coasts, as also the Islands. Well explored regions for bryozoa include (i) Waltair¬Visakhapatnam on the East Coast along the North Andhra coast, where over 100 species have been reported in recent works and (ti) the South-West Coast
from where about 130 speies were reported from samples mostly collected from the shelf zone (with dredges) as well as the intertidal. Bryozoa have also been reported from several estuarine localities (eg. Godavari estuary, Ashthamudi estuary) and as 'fouling species' in harbours wherever such studies were conducted. It is, however, to be noted that vast stretches of the long Indian coastline still remain unexplored and without doubt many species hitherto undetected, occur in these areas. Especially examination of shelf¬sediments (from the littoral zone upto Continental Shelf) should be rewarding. Fresh water bryozoa (phylactolaemata) have been well-worked out in Madhya Pradesh-Narmada river system and Rajasthan, from where about 35 species are recorded. The present knowledge of the distributional aspects of bryozoa in the Indian Ocean region is meagre. This is not only due to inadequate surveys but also for frequently doubtful determinations of species, especially in the early works. However, in a general way, the following observations could be made.
Species known to occur exclusively or predominantly in the Indo-West Pacific constitute the bulk of the Indian collections. Examples include : Steganoporel/a sulcata, Parasmittina tropica, Tiullamoperel/a stapifera, Rhynchozoon globosum, Nolella papalle11sis, etc. A good number of circumtropical species with a much wider distribution (eg. Aetea Qllgllina, Electra pilosa, Trypostega venusta, Cribrilaria innominata, etc.) also are encountered, indicating that many bryozoans, despite their delicate constructions, are "obviously adapta!;)1e to a wide range of conditions" ==Biological Diversity And Its Special Features Modem bryozoa are now grouped under 3 classes i.e., Phylactolaemata (containing fresh water species); Stenolaemata and Gymnolaemata. A total of 126 fam~lies are recognised-100 from Gymnolaemata (15 from the order Ctenostomata and 85 from Cheilostomata) ; 21 from Stenolaemata and 5 from Phylactolaemata. These comprise of approximately 4,000 species. The order Cheilostomata (of the class Gymnolaemata) is by far the most dominant group constituting 80% of the total species recorded in India, as in many other parts of the world.
It is known that transportation by ships etc., effect bryozoan distribution. Species like BlIgllla stolonifera, Hippopodina fet:ge11~sis occurring in fouling communities appear to be examples of introduced species. These are now well-established and play an important role in the fouling communities.
Endemism is known to be rare in marine/brackish water bryozoa. Among the species reported 50-60 years earlier, only Membranipora hugliensis has not been located anywhere else and could probably be considered an endemic species. In the '60s and '70s, a number of new species have been described by recent investigators. These include : Electra indica, Bicel/ariel/a cookae, Kinetoskias klugei, Bilguia bengalensis, Vittaticel/a ganapatii, Alderina arabiensis, Lacrimula visakhensis, Hippoporina indica, etc., among gymnolaemata (marine or brackish water realm) and Swarupella andamane11sis, Plumatella ganapati, Hyalinella diwaniensis and Varl/nella indorana from among Phylactolaemata (freshwater bryozoa). These species have so far not been reported from outside Indian waters and can probably be regarded as endemic species.
Bryozoa are among the most commonly encountered components in the 'intertidal' essentially as 'cryptic fauna' and also on the phytal (colonising extensively certain algae species). In some localities, they form distinct 'bryozoan bands' which provide shelter for numerous organisms (eg. small crustaceans, polychaetes, young molluscs, tunicates, etc.). In their own right, they also support a number of epizooites and are especially favourable for settling of a number of planti-grade bivalves. Intensive studies on the ecology of bryozoans are necessary for a proper understanding of shore ecosystem, reef-biology and progression of biofouling communities. Bryozoan 'reefs' are significant nourishing areas for commercial fish. Such reefs, although not located in India so far, are known to exist elsewhere.
The greatest importance of bryozoans in shallow waters, perhaps, concerns their role in marine biofouling, a problem of immense economic importance. World-wide annual costs due to just one aspect of fouling, Le., ship fouling, are estimated to be over $ 1,000 millions. Bryozoans are 'among the most abundant, diverse and consistently present group of marine fouling organisms' Over 130 species have so far been listed from representative areas and the list would be much more exhaustive if information from all other localities is available. In India, 30 species have so far been identified from fouling communities. Eventhough they are known to constitute at times nearly 100 percent of organisms on a given surface especially in the initial stages of community development, ego Electra bengalensis at Vishakhapamam harbour, their contribution to fouling biomass (weight) may not be necessarily high. However, they are known to be playing an important and subtle role in the biofouling process. For instance, on hulls of ships made of copper or copper alloys, which are unfavourable to most other groups, encrusting species have been reported to provide a conducive surface for further settlements (examples of bryozoa settling on copper/copper alloy include Watersipore arcuata, Mambranipora sp., Hippoporina americana, Hippopodina ftegenensis, etc.). Bryozoans especially ctenostomes (Bowerbankia sp., Amatltia, Zoobotryon, etc.) are known to clog pipes, and conduits and entangle propeller blades. Thin encrusting species like Electra tene/la also interfere with maricultural operations.
The soft bodied Ctenostomes may form trailing masses of upto 1 m in length or when mixed with branching Cheilostomes, form a thick felt work. These growths in turn prOVide shelter for numerous small crustaceans, polychaetes, young molluscans, tunicates and algae. At some harbours, however, dense bryozoan growths were reported to prevent settlement of other organisms. Heavy settlement of filamentous bryozoa may also prevent or reduce the attack of ship worms. Many species are quite sensitive to all the local environmental regimes and endemic to relatively small regions.
Because of their sessile mode of life, short larval period and generally ltenohaline response to the environmental regime, they are considered excellent zoogeographical, ecological indicators among biofouling groups. The group has a great potential to be used as an important biological resource for environmental impact analysis.
Several bryozoan species occur as fossils and many geological formations are well-characterised by their bryozoa. However, the stratigraphic value of bryozoa, despite a voluminous literature, is often underestimated and their application to economic geology, particularly in petroleum research has perhaps not been.fully exploited. Recent investigations suggest that several bryozoan species produce substances with pronounced biological activity. Some of the chemicals have a great potential for application in medical and pharmacological fields. Thus, BlIgula neritinia, the most commonly encountered 'fouling species' in Indian harbours, contains a compound highly effective against leukemia cells at a low dosage level. Flustra foliacia is known to produce monotrepanes haVing anti-insect, anti-septic and anti-bacterial properties. Hemolytic activity has been demonstrated in species like Carbesea curoa. Both Bugula stolonifera and B. neritina showed an inhibitary effect on gram-positive microorganisms. Zoobotryon verticil/atum is one of the few marine organisms that produces alkaloids.
It is however to be noted that investigations on the natural products from bryozoa are of a very recent origin and a great deal remains to be done in this highly promising field.
Pollution (especially by oil pollutants), eutrophication, silting and sedimentation are the main threats to bryozoa. Indiscriminate over-turning of rocks and other hard substrata in the intertidal while picking up ornamental shells for Commercial purposes leading to exposure (to'air) or even trampling by batches of students during sudy tours are quite harmful. Habitat protection is the most urgent need for protection of bryozoan fauna as in the case with many marine organisms. Sites with high diversity of bryozoan fauna (eg. palm beach and Shingle areas at Vishakhapatnam, where over 90 species have so far been indentified in the intertidal area) have to be identified and area-specific measures to protect the habitat need be taken.
Conservation And Future Studies
Inventorying bryozoan fauna is the first and most urgently needed step in providing proper scientific basis for implementation of any conservation measures for the groups. Except for a few localities, information even on occurrence, leave alone aspects such as functional roles, is not available. To establish patterns of variation among regions and to test hypotheses relating to constraints in diversity, it is also essential to monitor the changes in the groups occurrence and abundance. Inventorying and monitoring has to be carried out at both 'extensive' and 'intensive' sites which need to be designated for the purpose. Our knowledge of bryozoa from the Indian region is far from satisfactory. Vast structures of the coastline remain yet to be explored and studies in respect of majority of fhe species have not progressed beyond taxonomy. Biology and ecology of several species still remain uninvestigated. Phylogenetic relationships of the classes, families and genera are not yet clear. These a'spects need to be investigated in detail.
Habitats to be conserved; Littoral region, especially the rocky outcrops, shingles in the intertidal; Mangrove vegetation, Coral formations and firm (hard) substrata on the sea-bed.
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