Marine Biology

Dr. K.P.Biswas, M.Sc.,Ph.D., D.F.Sc. (Bom), E.F. (West Germany),F.Z.S., F.A.B.S. (Kolkata), Former Joint Director Fisheries (L-1),Government of Orissa, Director of Fisheries, Andaman and NicobarIslands and at present Faculty Member of Marine ScienceDepartment, University of Calcutta, West Bengal University ofAnimal and Fishery Sciences has been associated with fish, fisheryand marine science for more than fifty two years.

His latest books, “Advancement in Fish, Fisheries and Technology” and “Advances inFishing Technology” have been published in 2012.

Marine Biology

K.P. Biswas

2013Daya Publishing House®

A Division of

Astral International Pvt. Ltd.New Delhi – 110 002

© 2013 AUTHOR

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Biswas, K. P. (Kamakhya Pada), 1936-Marine biology / K.P. Biswas.

p. cm.Includes bibliographical references (p. ) and index.ISBN 9788170358633

1. Marine biology. I. Title.

DDC 578.77 23

Published by : Daya Publishing House®

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— Dedication —Dedicated to Mrs. Manju Biswas

for her encouragement

Acknowledgement

The author deeply acknowledge the help of Dr. N.A. Talwar in computer setting,while preparing the manuscript of the book.

K.P. Biswas

Preface

According to a report attributed to Patricia Miloslavich of Universidad, Simon,Boliver, Venezuela, the co-scientist associated with census of marine life on a globalbasis, in which more than 300 scientists participated for last ten years. There aremore than 2,30,000 species in world oceans.

The results show that around a fifth of the world’s marine species are crustaceans,such as, crabs, shrimps, lobsters, krills and barnacles. Added mollusks (squids andoctopuses) and fish (including sharks) accounts for up to half the species in the seas.The endangered species, often used in conservation campaigning, such as, whales,sea lions, turtles and sea birds account for less than two percent.

The survey also revealed areas of concern for conservationists. In every region,they have got the same story of major collapse of what were usually very abundantfish stocks or crabs or crustaceans that are now only 5 to 10 per cent of what they usedto be.

These are mainly due to over-harvesting and poor management of those fisheries.That is probably the biggest and most consistent threat to marine bio-diversity aroundthe world. The main threats include over-fishing, degraded habitats, pollution andthe arrival of invasive species.

But more problems arise from rising water temperatures and acidification due toclimate change and the growth in areas of the ocean that are in low oxygen, andunable support life.

The most diverse region identified by the Census of Marine Life (COML) arearound Australia and south east Asia. It is also a hot spot for terrestrial bio-diversityand has been known for about hundred years.

It looks like that region with the coral reefs has always had a very high rate ofspeciation. It also has very diverse range of habitats, from the deepest areas of theoceans to large areas of shallow seas, which can support coral reefs.

Australian and Japanese waters contain more than 30,000 species each. Next inline are the oceans off China, the Mediterranean Sea and the Gulf of Mexico.

An upwelling area is supposed to be a biological unit, as stocks of animals aremaintained within it from year to year. The animals including fish might live in theupwelling area all through their lives.

Upwellings occurs in Andaman Sea between December and February.

The Andaman and Nicobar Islands comprise an arcuate chain of 348 islands ofvarious sizes spread in a distance of about 1120 km and located between LowerMayanmar and Upper Sumatra of Indonesia in the Bay of Bengal. The total land areaof these islands is about 8,293 sq km. The islands have a mass of hills enclosingvalleys and a large part of the territory is covered with dense evergreen tropicalforests. The vegetation is mostly Mayanmar and Malay type. The climate is typicallytropical, with heavy gales and rainfall. The soil varies from sandy to clay. Some of theshore support rich growth of mangrove vegetation and coral reefs of the fringingtype.

The life in Andaman Sea has been much less affected by man. In the obscurity ofits long distance from the mainland, its depths and the breadth, its ocean animals aredifficult to hunt to extinction, while most of the marine vegetation and the bulk of thediverse invertebrate fauna are not useful to man.This is the reason for choosing theless disturbed Andaman Sea as a site for studying the fauna and flora and theirbiology in marine environment. In the sea, it has been said, that man reaps withoutsowing, and this is largely true. It follows that in this case the responsibility ofownership, which came with the domestication of animals and the care of crops hasrarely displaced the unconsidered greed of the hunter. This is nowhere better shownthan in man’s persuit of marine fish, crustaceans and mammals.

The author during his tenure of directorship in Fisheries Department of Andamanand Nicobar Islands from 1981 to 1984, came in close association of Andaman Seafor developing fisheries wealth. He initiated catching more and more fishes andcrustaceans from the sea to aid for nutritious diet to the people and to generateemployment for the fishermen. Towards achieving this objective, the author, not onlymade indepth studies about the aquatic resources of Andaman Sea, estimated fromthe survey and explorations from time to time, but also personally took part inexploratory fishing to know about the fishing grounds, type of species available,their magnitude, area of concentration and suitable fishing gears for their exploitation.

The book, “ Marine Biology “ in twenty nine chapters, besides describing themarine environment and ecosystem has given an account of physiography andlocation of Andaman Sea, also gave an outline of different types of ecosystems (marine,coral reef, mangrove, sea grass and sea weeds, pelagic and benthic) occupying differentniches of the sea associated with marine life.

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The chemical features of the water and the sea bottom augmenting the primaryproduction, through microbial realm, phytoplankton and algae forming the base offood pyramid was discussed in the book. The ecosystem associated flora and fauna,like algae, sea grass, zooplankton, sponges, coelentrates, chaetognaths, holothurians,echinoderms, mollusks, crustaceans, benthic macrofauna, and interstitial and benthicmeiofauna have been highlighted in the appropriate chapters. Fishes and crustaceans,which form the main source of protein food for human population have been speciallydealt in the book, as to the species of commercial importance, their availability,behaviour and migration pattern and their capture.

Once available, now endangered and almost extinct mammal, sea cow, Dugongdugong in the sea grass bed of Dugong Bay in Little Andaman finds a place in thebook.

K.P. Biswas

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Contents

Acknowledgement vi i

Preface i x

Introduction xvii

1 . Marine Environment and Ecosystem 1Neretic Province–Oceanic Province–Benthic Environment–Intertidal Area–TheEcosystem of the Sea

2 . Marine Biology 7Some Gross Features of the Oceans–Elements Abstracted by Plants and Animals–Organic Productivity–Biochemical Cycles–Distribution of Nutrients–FactorsInfluencing the Distribution of Nutrient Elements–Upwelling and FishProduction

3 . Explorations 12Preliminary Findings

4 . Physiography and Location 21Oceanography of Andaman Sea–Thermal Structure–Salinity–WaveCharacteristics–Surface Water around the Little Andaman Island–Temperature-Depth Profile

5 . Microbial Oceanography 30

6 . Chemical Features 34Hydrographical Features–Biochemical Relationships–Calcium, Magnesium andFluoride Concentrations–Calcium–Magnesium–Fluoride

7 . Ecosystems 42Marine Ecosystems–Mangrove Ecosystems–Coral Reef Ecosystem–Sea Grassand Sea Weed Ecosystems–Pelagic and Benthic Ecosystems

8 . Primary Production 52Primary Production in Andaman Sea–Production by Phytoplankton–Chlorophyll a and Phaeophytin–Phytoplankton Population–Particulate OrganicCarbon (POC)–Zooplankton–Environmental Features–Extracellular Productionin the Andaman Sea–Detrital Content of Andaman Sea–Suspended andParticulate Organic Matter–Living Matter–Detritus–Primary Production–Secondary Production–Tertiary Production

9 . Wealth of Marine Life 62Reef Associated Fauna–Reef Associated Fauna–Reef Associated Sponges–ReefAssociated Ornamental Fishes

10. Microbial Flora and Fauna 73Ecology of Microbial Plankton–Ocean’s Microbial Realm–Microbial Fauna onthe Sediments of Andaman Sea

11. Nanoplankton 80Nanoplankton from Recent Sediment off Andaman Islands

12. Phytoplankton and Algae of Tropical Seas 83Sea Grass–Dinoflagellates–Coccospheres–Distribution of Phytoplankton andChlorophyll a around Little Andaman

13. Zooplankton 98Zooplankton Abundance in Andaman Sea–Components–Secondary Production–Distribution of Zooplankton in Relation to Thermal Barrier–Crustaceans andTotal Zooplankton Diversity in Andaman Sea–Species Diversity

14. Corals of Andaman Sea 105The Gorgonian–Biological and Physical Features of Coral Reefs–List ofEcological Variables–Scleractinian Coral Species Recorded from Andaman Sea–Fungiids–Rainforest of the Sea

15. Sponges 118Culture of Marine Sponge

16. Coelenterata 123Ocean’s Gelatinous Inhabitants–Jelly Fishes

17. Sea Anemones 128

18. Meiofauna 130Interstitial Meiofauna–Meiobenthic Fauna

19. Chaetognaths 136Distribution

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20. Holothurians 140

21. Echinoderms 144Starfish – Crown-of-Throns

22. Molluscs 150Cephalopods–Sepia aculeate–Sepiella inermis–Sepia elliptica–Doryteuthissinghalensis–Octopods–Octopus dollfusi–Octopus aegina–Nautilus pompilius–Gastropods–Bivalves–Surf Clam–Giant Clam–Oysters–Cowry Shells–Phylum– Mollusca; Class – Gastropoda; Order – Archaegastropoda, Super family –Cypraeaceae (Cypracoidea) and Family – Cypraeidae (True cowries)–Sub-family– Erroneinae–Sub-family – Adustinae–Sub-family – Narinae–Sub-family –Mauritiinae–Sub-family – Erosariinae–Sub-family – Cypraiinae–List ofGastropods found in Andaman Sea–Bivalves–Mabe Pearl–Mussels–GreenMussel–Edible Oysters

23. Crustaceans 192Genus – Penaeus–Penaeus indicus–Penaeus monodon–Penaeus semisulcatus–Penaeus penicillatus–Penaeus japonicus–Penaeus canaliculatus–Genus –Metapenaeus–Metapenaeus dobsoni–Metapenaeus affinis–Metapenaeusmonoceros–Metapenaeus ensis–Metapenaeus lysianassa–Metapenaeusburkenroadi–Metapenaeus stebbingi–Metapenaeus kutchensis–Metapenaeusalcocki–Genus – Parapenaeopsis–Parapenaeopsis stylifera–Parapenaeopsishardwickii–Parapenaeopsis sculptilis–Parapenaeopsis uncta–Parapenaeopsisnana–Parapenaeopsis cornuta maxillipedo–Parapenaeopsis acclivirostris–Parapenaeopsis tinella–Genus – Macrobrachium–Macrobrachium rosenbergii–Macrobrachium malcomsonii–Macrobrachium villosimanus–Macrobrachiumlamarrei–Macrobrachium rude–Macrobrachium idella–Macrobrachiumequidens–Macrobrachium mirabile–Macrobrachium javanicum–Macrobrachiumsabriculum–Genus – Palaemon–Palaemon tenuipes–Palaemon styliferus–Genus– Acetes–Acetes indicus–Acetes erythraeus–Acetes sibogae–Acetes serrulatus–Acetes japonicus–Acetes cochinensis–Genus – Pandalidae–Parapandalusspinipes–Plesionika martia–Plesionika ensis–Genus – Heterocarpus–Heterocarpus gibbosus–Heterocarpus woodmasoni–Genus – Hippolysmata–Hippolysmata ensirostris–Hippolysmata vittata–Genus – Trachypenaeus–Trachypenaeus pescadorensis–Trachypenaeus sedili–Trachypenaeuscurvirostris–Genus – Atypopenaeus–Atypopenaeus stenodactylus–Genus –Metapenaeopsis–Metapenaeopsis stridulans–Metapenaeopsis mogiensis–Metapenaeopsis andamanensis–Metapenaeopsis philippii–Genus –Parapenaeus–Parapenaeus longipes–Parapenaeus fissures–Parapenaeusinvestigatoris–Genus – Penaeopsis–Penaeopsis rectacuta–Genus – Solenocera–Solenocera indica–Solenocera pectinata–Solenocera hextii–Solenocera choprai–Solenocera koelbeli–Solenocera melantho–Genus- Hymenopenaeus–Hymenopenaeus acqualis–Genus – Sicyonia–Sicyonia lancifer–Genus –Aristeus–Asisteus semidentatus–Aristeus alcocki–Aristeus virilis–Aristaemorpha woodmasoni–Penaeopsis jerryi–Acanthephyra sanbuinea–Decapod Crustaceans in Andaman Sea–Marine Ornamental Shrimps–Lobsters–

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Crabs–Distribution–Reproduction, Development and Morphology–Ecology andLife Cycle–Deep Sea Crab–Sand Crab–Spider Crab–Poisonous Crabs–Ecology–Marine Decapods of Southwest Coast, off Karnataka–List of Decapod CrustaceansCollected from Marine Zones along Karnataka Coast–Prawns (8 families and 33species)–Hermit Crabs (2 families and 14 species)–Lobsters (3 families and 9species)–List of Decapod Crustaceans Collected from Andaman and NicobarIslands–Prawns–True Crabs–Hermit Crabs–Isopod–Sea Spider

24. Syngnathids 233Captive Breeding–Endangered Species of Sea Horse

25. Fish Fauna in Indian Seas 238Fish Fauna in Near Shore Waters–Appearance of Fishes in Near Shore Watersduring Monsoon at Karwar, Karnataka–Fish Fauna in Coastal and Off-ShoreWaters of India–Fish Fauna around Andaman and Nicobar Islands–Elasmobranchs–Teleosts–Fish Stock Assessment in Andaman Sea–Fish Faunaaround Lakshadweep Islands–Distribution, Occurrence and Biology of someFishes–Elasmobranchs–Rays and Skates along Tuticorin Coast–Sharks inMaharashtra Waters–Hound Shark from Calicut Coast–Quagga Shark fromCochin–Bramble Shark in the Veraval Coast–Reproduction and Breeding ofElasmobranches–Perches–Sea Bass, Lates calcarifer–Otolithoides biauritus andProtonibea diacanthus–Honeycomb Grouper–Grouper–Snapper–Serranid Fish–Ghol–Threadfin Bream–Cat Fishes–Clupeids–Oil Sardine–Hilsa: The IndianShad–Milk Fish–Mullets–Scombroids–Tunas–Seer Fish–Biology–Flat Fishes–Pelican Flounder–Sole–Carangids–Mackerel–Bombay Duck–Ribbon Fishes–Pomfrets–Cobia–Sucker Fish–Moontail Bullseye–Tetradons–Spotfin PorcupineFish–Silver Pompano–Lizard Fish–Slope Fish–Cornet Fish–Sun Fish–ThreadfinGroup–Leather Jacket–Goat Fish–Dolphin Fish–Sand Tile Fish–MoluccanSweeper–Oil Fish–Anchovies–Silverbellies–Moray Eels–New Records–LessImportant Fishes–Rare Fish–Blue Ringed Angel Fish–Marine Ornamental Fish–Butterfly Fish–Silver Moony–Gold Fusilier–Convict Surgeon–Blue StripedSurgeon Fish

26. Benthic Macrofauna 312

27. Marine Reptiles 318Turtles–Nesting Sites of Sea Turtles in India

28. Marine Mammals 324The Dugong–Occurrence of Mammals along Indian Coasts

29. Special Traits for Marine Life 329Floating Mechanisms of Sea Creatures–Deep Sea Diving of Marine Animals–Hydrodynamic Function of Marine Fishes–Colouration and Light Emission inMarine Animals–Colourations

References 347

Index 357

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Introduction

Marine ecosystem has varying diversity. The coast line comprises almost alltypes of intertidal habitat, from hypersaline and brackish lagoons, estuaries andcoastal marsh and mudflats to sandy and rocky shores. The subtidal habitats areequally diverse. Each local habitat reflects prevailing environmental factors and ischaracterized biota.

Thus marine fauna itself demonstrates gradients of change throughout the Indiancoasts and islands.

Out of the total 32 animal phyla, 15 are represented by the taxa in the marineecosystem. They may constitute either migratory (pelagic crustaceans, coelenterates(medusae), cephalopods, fishes, reptiles, birds and mammals. The benthic macro-fauna comprises of resident species of polychaetes, bivalves, gastropods, sipunculusand mud burrowing fishes. Among invertebrates, the sponges, phoronids andechinoderms generally do not prefer an estuarine ecosystem.

Free swimmers or nekton are important components of marine biodiversity andconstitute important fisheries of the world. The dominant taxa in the nekton are fish,others being crustaceans, mollusks, reptiles and mammals. Out of the total 22000 finfish species, about 4000 species occur in the Indian Ocean, of which 1800 specieswere reported from the Indian Seas. A majority of nekton species is found in thecoastal waters. It is estimated that 40 species of sharks and 250 species of bony fishesrepresented the oceanic varieties.

The global ocean balance between nitrogen fixation and the loss of fixed nitrogenthrough anaerobic ammonium oxidation (anammox) reaction and denitrification,due to water upwelling to the surface, are generally slightly depleted in nitrogenrelative to phosphorus, where upwelling of nitrogen and phosphorus is substantial(eutrophic region), primary production is high, resulting in the sinking of large amount

of organic matter. As this organic matter is broken down to its nitrogen andphosphorus are solubilized, a large fraction of available oxygen is consumed. In thissuboxic waters, anammox and denitrification converts ammonia and nitrate tonitrogen resulting in a loss of biologically reactive nitrogen from the system and amarked decrease in the deep ocean N:P ratio. In Oligotrophic sea, on the other hand,the upwelling of nitrogen and phosphorus is low, primary production is reducedand often dominated by nitrogen-fixing cyanobacteria, which are favourd in lownutrient, nitrogen-depleted surface waters.

Andaman Sea, an oligotrophic one, was the least studied basin for its potentialbiological wealth and resources. The earliest sketchy account of fishery potential ofAndaman Sea was reported from the results of a fishing trawler in 1908-1909.Thereafter, several cruises followed till 1979 with an ultimate objective of finding outthe available marine biota and productivity.

The Andaman and the Nicobar groups of islands are located in the south-westernpart of the Bay of Bengal, between Latitude 6 and 14 degree North and Longitude 91and 94 degree East. The two groups are comprised of 348 islands, of which only 40are inhabited. They collectively have an area of 8293 Sq km, which does not includea number of exposed islets and rocks. All the islands are the exposed peaks of longranges of submerged mountains, which extend from Mayanmar to Sumatra. A deepoceanic ridge, about 1500 meter in depth runs between the Nicobar and Sumatra andanother oceanic ridge along 10 degree North separates the Andaman and Nicobargroups of islands. Most of these islands are surrounded by fringing reefs on theireastern side and barrier reef on their western side. They harbor a rich population ofcorals and mollusks, and most of them have luxuriant mangrove vegetation aroundthem. Geographically, the sea on the east of both these groups of islands is termed asAndaman Sea. The sea on the north forms a part of the Bay of Bengal through thePreparis Channel and on the south it is connected with the South China Sea throughthe Malacca Strait. The Andaman Sea occupies an area of 6.02 X 100000 Sq km andhas a volume of 6.6 X 100000 cubic km with an average depth of 1096 meters.

The Andaman and Nicobar Islands separate the Bay of Bengal from the AndamanSea. The islands are fairly straight and gentle on the western side comprising coastalplains, whereas the eastern coasts are strongly indented and steep and in manyplaces coral reefs and raised beaches, as high as, 20 meters above the sea level havebeen reported. Narrow channels separate the Andaman into North, Middle andSouth Andaman Islands, which are collectively known as the Great Andaman.

The Paleogene Andaman-Nicobar trough was folded and reverse faultedwestward resulting in the emergence of the Andaman Islands during the Oligoceneand late Miocene. The Andaman-Nicobar ridge is formed of serpentinite basementoverlain by distorted Paleocene to Miocene and flat lying Pliocene to recent sediments.A sequence of Paleocene through Upper Miocene rocks including 3000 meter of UpperEocene and Oligocene graywackes were deposited over the Andaman serpentinitesunder fluctuating shallow to deep water conditions.

These islands, which are a part of anticlinal belt passing from Arakan Yoma inMayanmar through Andaman and Nicobar islands and Mentawai islands, west of

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Sumatra, separate the Andaman Sea from Bay of Bengal, except the connectionsthrough Preparis Channel on the north with a depth of about 200 meters, the GreatChannel on the south, 1800 meters deep and the ten degree channel in the middlewith a depth of about 800 meters. A north-south arc of volcanic arcs and sea mounts,including Barren and Narcondum islands, in the Andaman Sea separates the largecentral basin from two smaller basins to the north and south. The fall of slope is alsosteep on the eastern side of the islands. The thermo-haline properties of the Andamanwaters, within the surface mixed layer, thermocline and halocline downwards onthe eastern and western sides of the island chains are the features special to theregion.

The Andaman Sea is influenced by large quantities of freshwater runoff from theperennial rivers of Mayanmar, Thailand and Malaysia. This runoff largely influencesthe topmost layers. Below the surface layer, oceanic conditions prevail.

Oceanographic investigations in the Andaman Sea dates back to 1869, whenFrancis Day, a well known army officer and fishery biologist visited these islands. Herecorded the occurrence of 136 species of fish in the Andaman waters.

Oceanic islands, or rather a group of islands, far away from continental margins,significantly influence, modify and change the general physico-chemical propertiesof the waters around them, mainly through changing the general circulation patternsand associated stratification-mixing processes. Especially, with a chain or cluster ofsuch islands forming partial barriers and obstacles, the physical processes andhydrodynamic characteristic of the adjoining waters change in distinctive fashionsmore as a rule than as an exception. From the Hawaiian group of islands to theAndaman- Nicobar Island arc system, there are numerous examples to be found inall the major oceans and seas. The oceanic islands of the Pacific and Atlantic, at leastsome of them, have been quite intensively studied from physical, geological andmarine biological points of view.

Keeping the Andaman group of islands in mind, more is known about the south-east Asian waters, from the Philippines to the Timur Sea and the strait of Malacca tothe Arfuna Sea, as would be evident from the NAGA Report (Wyrtki, 1961). It isequally true and disappointing to mention that since the pioneering work of Sewell(1925) more than 94 years ago, precious little has been added to our knowledgeregarding the Andaman Sea and the Andaman-Nicobar group of islands. Yet this isthe region, where the complex air-sea interaction phenomenon release enormousamount of energy for the genesis of the devastating tropical cyclones, which hit theeast coast of India and the north and north-eastern coast of the Bay of Bengal almostevery year. What makes the seas around these islands even more interesting and aclass apart from many other oceanic islands (barring a few) is the yearly cycle of theNorth-East and South-West monsoonal wind systems reversing the atmosphericcirculation and the surface currents of the Bay of Bengal and the Andaman Sea fromDecember to April and June to October with intervening transitional periods. Anotherfeature which demarcates the Andaman Sea from the Bay of Bengal lies in thegeological history of emergence and development of these two regions. The islandarcs form a kind of barrier between the Bay of Bengal, which has more or less evenbottom topography and the Andaman Sea with its three major basins.

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Two cruises of RV Gaveshani in January and February, 1979, in the AndamanSea revealed some detailed facts as to the habitat under sea, water qualities andfaunal diversity in the region. The area studied was in between Latitude 6 to 14degree North and east of Longitude 91 degree 30 minute East. The cruises were madefrom 29 January to 27 February, 1979, and during this period, the vessel covered adistance of 6300 line km and worked at 63 stations. Of these 50 were in the AndamanSea and the rest in the Bay of Bengal.

At all the stations, water and plankton samples were collected using Nansenreversing bottles and large Van Dorn water samplers, Indian Ocean Standard Net,Heron-Tranter net and Neuston net. Bathythermograph, thermo-salinograph and aship borne wave recorder were run at all stations. The conductivity-temperature-depth profiling system (CTD) with rosette samplers were operated at selected stations.In addition, intensive studies were conducted around the Little Andaman on thecirculation pattern around the island and on its benthic communities. Off Hut Bay, inthe Little Andaman Island, the ship took the measurement of currents and the flowpattern by launching a parachute drogue. Routine meteorological observations werealso made at all the stations.

Some samples were extracted with hexane for the analysis of petroleumhydrocarbons, while many samples were filtered for the estimation of heavy metals,extra-cellular products, particulate organic carbon, dissolved glycolic acid andglycollates, chlorophyll and detritus. Samples were inoculated with carbon 14 andincubated on board for the study of photosynthetic productivity. Zooplanktonsamples, collected using three types of net were preserved for subsequent examinationof biomass, secondary production, species composition etc. Samples collected withthe Neuston net along the oil tanker route across the Bay of Bengal, were examinedfor floating tar balls and other particulate matter. Those which were found free fromoil were preserved for the estimation of pesticides. Sediment samples collected, usinga snapper and a grab, were processed on board for the examination of macro/micro/and meio-benthos. Some of these samples were preserved for the analysis of radio-active isotopes. Fishes, caught by hook and line, were processed on board for theestimation of mercury and pesticides in their tissues. Experimental fishing with tunalong line was tried for three hours at a station, south of Great Nicobar Island.

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1

Chapter 1

Marine Environmentand Ecosystem

The oceans comprise, the largest of all biospheres or regions of life on the earth,being some 300 times greater by volume than the living space on and over the land.The environment of the sea is divided ecologically, according to depth, distance fromthe land andºof light penetration, in general, characteristic type of organisms occurin these various environmental divisions.

The primary division is the overlaying water mass, the pelagic zone and theland mass beneath it, the benthic zone. The pelagic realm is sub-divided horizontallyinto a neretic province and an oceanic province. The neretic province is composed ofall the waters above the continental shelf extending offshore to a depth of 200 m. Theoceanic province consists of all the waters beyond the continental shelf with a depthgreater than 200 m.

Neretic ProvinceThe neretic province, being contiguous with the continent and land mass, is

well lighted, but a turbulent section of the ocean. Seasonal variation coupled with theinfluence moon characterizes the area by strong wave action, marked currents andbroad changes in temperature, salinity and nutrients. Dissolved oxygen is high.Detritus in suspension plus extensive micro and macro-biological production impartsa characteristic green, grey, brown or red colour to these near shore waters.Representative waters include waters of shore line, kelp beds, coral or rock reefs etc.The number of potential habitats is thus large and varied.