Summary and Conclusion

Transcription

1 Summary and Conclusion Members of the order Mysidacea are important component in marine and estuarine plankton inhabiting all regions of the oceans. There are many brackish water species and few species occur in fresh water, some have become adapted to the specialized environments of caves and wells. They are omnivores, responsible for remineralisation of a substantial portion of the detritus in the water column. They form an important link in the food chain (between microbial producers and secondary consumers) and therefore play a major role in the cycling of energy within the aquatic ecosystem. In tropical and subtropical waters, swarms of mysids are exploited commercially and marketed as preserved cooked food. Mysids have been used in fish farming as live feed resource. They are also excellent experimental organism, extremely useful in the studies of potential impact of various pollutants in the aquatic environment. Mysids are also used in wood pulp effluent plants. Considerable work had been done on the taxonomy of Mysids in the Indian Ocean since 1900 (Tattersall, , Hansen, 1910, Pillai, , 1973; Panampunnayil, ) and in 1987, Mathew er al. carried out a study on the distribution and abundance of mysids from the Indian EEZ. However, none of these accounts appears to give combined information on the taxonomy, ecology, species abundance and their distribution in the Indian waters in relation to the different environmental variables. Despite their overwhelming ecological significance in ecosystems, very little work has been done on mysids in the Indian waters. Considering the significant role of mysids in the productivity of tropical ecosystem, the present study has been undertaken to extend our knowledge on the systematic, life history, distribution, abundance and DNA analysis and biochemical composition of readily available species. 273

2 Summary and Conclusion The material for the present study have been collected from the Indian EEZ of the Arabian Sea, Bay of Bengal and the Andaman Sea, shallow coastal waters of northwest coast of India and Cochin backwaters. Mysids in the Arabian Sea, Bay of Bengal and the Andaman Sea Information on the systematics and ecology of Mysidacea of the Indian EEZ is very limited. ln the present study, species composition and diversity of this group is evaluated based on 1325 stratified samples and 336 surface samples. Total 27 species of mysids belonging to 21 genera were recorded. Boreomysis plebeja (Bay of Bengal), Anchialina media and Synerythrops intermedia (Andaman Sea) are new records from the Indian waters. Pseuderythrops gracilis is a new record for the Andaman waters. Euchaetomera glyphidophthalmica and Rhopalophthalmus indicus are first records for Bay of Bengal. Most of the mysids are surface dwellers, surface collection constituted 90.71% and stratified collection constituted only 9.92% of the total catch. Population density of mysids in the Bay of Bengal was higher (37.59%) than that of the Arabian Sea (29.29%) and Andaman Sea (33.1%). Dominant species like, Siriella gracilis, Hemiseriella parva, Anchialina typica and Pseudanchialina pusilla occurred through out the year. Pseudanchialina pusilla was the most abundant species (64.77%) and Siriella gracillis was the second dominant species (28.1%). Species diversity is more in Arabian Sea (17) as compared to Bay of Bengal (9) and Andaman Sea (14). Below 500m, only two species Gibberythrops acanthura and Boreomysis plebeja were recorded. Out of the twenty-seven species, four are common to Indian, Pacific and Atlantic oceans, 13 are confined to the Indo-pacific and 10 are restricted to the Indian Ocean, of which 4 are endemic in the Indian waters. 274

3 pp g ggsmnmar)> and C0nclusz'0n North westcoast of India The majority of mysids species are divided into two broad categories. The first consists of species occurring in offshore, deep neritic, epipelagic, mesopelagic and bathypelagic environments. The second comprises shallow neritic, coastal, littoral and estuarine species, many of which have extremely localized distribution. The shallow water Mysidacea of the Indian region is rich and varied. Our knowledge on the taxonomy, ecology and distribution of many of these species is incomplete. Zooplankton samples were studied from 10 locations. Mysids found in all areas except at Veravel. Maximum density (8792/l00m3) was found at Dahanu constituted by a single species Mesopodopsis orientalis. A total of 8 genera and 12 species were represented in the collection. Three species, Siriella hanserzi, Erythrops minuta and Acanthomysis anomala are first records from the area. The mysid fauna of the shallow water is dominated by a single species, Mesopodopsis orientalis. Indomysis annandelai was the second in abundance. Rhopalophthalmus vzjayi also occurred in small aggregations. All the other species are either moderately or sparsely represented. Of the 12 species, 3 are common to lndo-pacific waters, 9 are confined to the Indian Ocean of which 5 are endemic in the Indian waters. Cochin backwaters Cochin backwater is one of the largest estuaries in India. The importance of mysids in the tropical estuaries is generally thought to be significant since these habitats play an important role in completing the life cycle of many of the commercially important fishes and prawns. Ecological importance of mysids, particularly their role in food chains as a link between the benthic and pelagic system is becoming increasingly apparent. Their trophic role as a converter of energy into forms which can be used by higher organisms especially fishes coupled with ubiquity and abundance of mysids in 275

4 W U g Summary and Conclusion the estuaries indicates that their significance in the productivity of such ecosystem has been greatly under estimated. Present study is the first report of mysids from the Cochin backwaters. Four species of mysids belonging to 3 genera were recorded from Cochin backwaters, of which Kochimysis pillaii is a new genus and new species. In M. orientalis and M. zeylanica, reproduction and recruitment were continuous through out the year, main peak being associated with low salinity. Male and female of M. oriemalis and M. zeylanica attained sexual maturity at a length of and mm respectively. The brood size in M. oriemalis, M. zeylanica and R. indicus, was related to the size of the incubating females. R. indicus attained sexual maturity at a length of 8.6 mm in male and 8.5 mm in females. High abundance of gravid females of R. indicus during high saline premonsoon period suggests that salinity plays an important role in the development of marsupium and broods. In M. orientalis, brood size was 8 to 12, where as that of M. zeylanica and R. indicus are 7 to ll and 6 to 13 respectively. Mysid abundance clearly depends upon the phases of tides (flood /ebb), character of tides (semidiurnal and diumal) vertical migration (day and night variation) and breeding activity. Mysids undergo circadian changes of their position in the water column. DNA barcoding This is the first attempt to analyze DNA sequence of Indian mysids. DNA barcoding provides an efficient method for species level identification and is a powerful tool to taxonomic and biodiversity studies. The consistent pattern of variations in the mtcoi sequence will be suitable for evaluation of the taxonomic significance of geographic variation within species, identification of sibling and cryptic species and genus. 276

5 g g g Summary and Conclusion Biochemical composition Biochemical analysis of three mysids, Mesopodopsis orientalis, M. zeylanica and Rhopalophrhalmus indicus showed significant variations in their biochemical composition. Protein is the primary body component in alldevelopmental stages. In all species, matured males and females had higher protein content than in other stages. Carbohydrate content is high in the immature stages and lipid content was more in brooding females. The present study extends our knowledge on the little known mysid fauna of the Indian waters. The main conclusions are the following. A total of 39 species of mysids representing 26 genera were encountered in the collections, of which 4 species are cosmopolitan, 15 are Indo- pacific and 20 restricted to Indian Ocean, of which 10 species are endemic in the Indian waters. A new genus and a new species Kochimysis pillaii have been recorded from the Cochin backwaters. From the present study, three species of mysids, Boreomysis plebeja, Anchialina media and Synerythrops intermedia are added to the species list of Mysidacea in the Indian waters. Euchaetomera glyphidophthalmica and Rhopalophthalmus indicus from Bay of Bengal, Pseuderythrops gracilis from Andaman waters and Seriella hanseni, Eryrhrops minuta and Acanrhomysis anomala from coastal waters of northwest coast of India are first report from the respective areas. Population density of mysids was high in the Bay of Bengal whereas species diversity was more in the Arabian Sea. Salinity plays an important role in the development of marsupium in Rhopalophthalmus indicus and brooding females occurred in larger numbers during the high saline pre-monsoon period. In the future, DNA barcodes may provide rapid, automatable protocols for zooplankton species identification and comprehensive DNA sequence databases and fabrication of DNA microarrays or chips which will allow molecularly based recognition of known species. However, new or unknown species will require analysis by an expert taxonomist, who is able to identify 277

6 pg pp p m pp S umma ry and Conclusion and/or describe the species using morphological characters. Biochemical analysis of three species of mysids, Mesopodopsis orienralis, M. zeylanica and Rhopalophrhalnms indicus showed significant variations in their biochemical composition. Protein was the principle component in all development stages. Species diversity is low in coastal and estuarine waters whereas it is high in Oceanic waters and reverses is the trend in the case of population density of mysids. Due to short life cycle and their abundance, Mesopodopsis oriemalis, Mesopodopsis zeylanica and Rhopalophrhalmus indicus is suitable tool for environmental assay experiments. Analysis of biochemical composition also suggests possible utilization of these species as an altemate live feed due to its nutritive value, which may partially meets the demands of fodder for Wide variety of cultivated fishes and crustaceans.