Biological Oceanography By Prof. A. Balasubramanian

Objectives After attending this lesson, the user should be able to know the importance of biological oceanography as a major branch of oceanography. The concepts of , their ecological conditions, distribution controls and the various interactive mechanisms of marine life will be understood in this lesson.

Introduction to Marine environment and occupy about 71% of the Earth’s surface. These are called as marine environments. The total volume of water under this marine environment is 1370 million cubic km. The space available for marine life is 300 times more than the space available for other aquatic or terrestrial life living on the land. It is also believed that the earliest organisms were originated in saline waters of the ancient oceans, many million years before. Oceanography deals with the physico-chemical characteristics of oceanic waters, their interactions with the atmospheric air, temperature, dynamic movements like tides, waves and currents, habitat for marine flora and fauna found at various zones of seas and oceans. Oceans play a major role in controlling global climate, offering plenty of natural resources and providing food to the global population. The biological interactions among water, air and life are studied under the branch of biological oceanography.

Biological oceanography Biological oceanography is a major scientific discipline dealing with all aspects of marine life under different zones of the oceanic environments. The interest to study biology by humans started as early as fourth century BC when Aristotle described about 180 species of marine animals. The geographical knowledge of oceans got improved after several great expeditions conducted by the people from 15th to 16th centuries. Through explorations people conducted detailed underwater surveys and mapped the ocean floors with respect to their physical features, chemistry and biological conditions.

The First Texts of Oceanography The first texts of Oceanography were published by Charles Wyville Thomson in 1873, entitled as the “The Depths of the sea”. Through the Challenger Expeditions of 1872, people traveled for 110, 900 km and visited all the major oceans of the world , except Arctic. The Challenger expedition also attempted to integrate the geology, biology, chemistry and the physico-chemical phenomena of the oceans. It was carried out for about 19 years by a group of 76 scientists. The first seafloor map was produced with details of life existing at greater depths. About 715 new genera and 4417 new species of marine organisms were described by the great German Biologist Ernst Haeckel. Since 1872, different countries have been engaged in conducting many major biological oceanographic expeditions. The study of marine life has offered more and more data and scientific facts about the dynamics of oceanic environments.

Historical development Edward Forbes, a British Naturalist (1815-1854) is the founding father of Oceanography. He has systematically studied the marine biota and benthic marine animals. It was he, who specified that different biological species occupy different depth zones of the seas and oceans. His Nephew, James Ross, during 1839-43, collected the samples of benthic animals as deep as 730 m, and gave a lot of Page 1 of 9

information to others about the existence of marine life at deeper levels. When facilities were very limited to carry out any underwater explorations, this was done. Ecology of marine life was understood and it become a major part in the study of oceanography and biology.

Component of marine environment Marine are characterized by both biotic and abiotic components. The dominant biotic components are organisms and their species, predators, parasites, competitors and Mates. The dominant abiotic components (ie., the physical and chemical components) are temperature, concentration of nutrients, penetration of sunlight, turbulence and turbidity, salinity and density of water masses, climatic parameters including the action of wind. Marine ecosystems are typical environments ranging from a small tidal inlet to the deep water ocean basins. Depth of is a major factor in addition to its movement and circulation. Solar and atmospheric interactions are very important aspects in the biological oceanography.

Conditions of marine environment The marine environments show altogether a different kind of physical condition for their life to survive. The major factors influencing the oceanic waters are their temperature, transparency, salinity and density which vary with reference to space, time and depth. The ocean water temperature decreases and light penetration diminishes with reference to depth in oceans. the hydrostatic pressure of water increases with depth. The nutrients become more concentrated when the depth increases.

Conditions of Marine Life Water , which is a fundamental constituent of all living organisms, is available in plenty , within the marine environments. Marine life species are buoyed up by moving water and need not have to store a large amount of energy in their skeletal material. Majority of the marine plants are also floating species. Size-wise, they are microscopic. Many of the marine animals are invertebrates. They do not possess massive skeletons. For the purpose of floating and swimming, the marine animals require very little energy.

Temperature and light penetration Temperature of oceanic waters is an important parameter which do not vary as drastically as seen on the land masses or as seen in the atmosphere. However, there are certain properties which are less favourable for life to survive in the seas and oceans. The growth of plants in the sea is limited by the availability of sun light. It is a fact that 50% of the total solar radiation which penetrates into the sea surface gets disappeared rapidly with reference to depth. Much of the marine environment is under perpetual darkness. Under such circumstances, the entire marine life depends on the availability of essential nutrients only. It also adds to the release of decayed organic matter, in huge volume, within the seas and oceans. Much of the decaying matter sinks inside the seas and gets mixed up or deposited. The zone just below the sea surface experiences the maximum environmental fluctuation. This is the zone where more air-water interactions exist. The same surface zone experiences much variations in temperature, salinity and turbulence of water from the winds. All the environmental parameters also show distinct vertical variations within the oceanic water masses. Because of these variations, it is necessary to classify the marine zones for any detailed analysis.

Classification of marine zones

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Marine environments can be subdivided into two major divisions as Pelagic and Benthic environments. The word “Pelagic” means ‘Open sea’ and the word “benthic” means ‘bottom’. The Pelagic condition refers to the ocean water column starting from the surface of the oceans and ending at the greatest depths. The Benthic condition refers to the conditions of the deep ocean floors. In the open sea, the zone extending from the high water and low water coastal belt, upto a depth of 200 m inside the sea, is called as the Neritic zone.

Pelagic zone The is further subdivided into five major layers, as epipelagic, mesopelagic, bathypelagic, abyssopelagic and hadal zones. The Epipelagic zone is the zone of water column that is existing upto 200m down from the ocean surface. The is the zone that is existing upto 1000 m down below the epipelagic zone. The Bathypelagic zone is the underwater zone that is existing from 1200 m to 4000 m down below the ocean surface. The Abyssopelagic zone is the zone that is existing beyond 5200 m depth and upto 6000m from the oceanic surfaces. The Hadal Pelagic zone is the zone of deep water extending beyond 6000m and may go upto 10000 m below the ocean surface. Biological oceanography deals with the physic-chemical and biological conditions of marine life of all these zones.

Benthic zone The Benthic environments are classified into five zones as supra littoral, littoral, sub-littoral, bathyal, abyssal and hadal types. The Supra littoral zone is the zone existing on the beach with the high tide water line. The Littoral zone is the high water to low water tide line region. The Sub littoral zone refers to the zone of low tide water line to 200m depth on the continental shelf region inside the sea. The is the zone ranging from 200 m to 3000 m depth of water column inside the sea. The is ranging from 2000m to 6000m depth inside the sea and it exists mostly on the continental slope regions. The is the life zone existing beyond 6000 m of water depth. This zone may go upto the end of 10000+ m depth of water column in the deep ocean basins. This is the last and dark zone of the oceans. Biological oceanography deals with all the living conditions of marine life and their biological processes prevailing in all these zones.

Ecology of seas The Pelagic environment supports the life of all Planktons and Nektons. It is seen that the epipelagic zone is almost a sunlit zone. Enough amount of sun light penetrates into the top layer of oceans. This situation helps all floating plants to carry on their photosynthesis. The mesopelagic zone is known as the twilight zone. This is a dim zone where there is very little light penetration. This condition is not suitable for many plants to grow. The bathypelagic zone is known as the midnight zone. This is the layer between 1000m and 4000m depth below the sea surface , where there is no penetration of light. The abyssal zone is the pitch-black bottom layer of the oceans. The oceanic water masses present in this zone are also at freezing temperature and with great pressure. The Hadal zone is the last deepest zone. This is the most inhospitable zone of the oceans. Biological oceanography deals with all these zones, prevailing marine life and their biological processes.

Life in oceans Plants are found only in the sunlit zones where there is sufficient light for photosynthesis. Animals are found at all depths of the oceans though their numbers are greater near the surface where food is available in plenty for them. More than 90% of all the marine species dwell on the ocean bottom where a single rock can be a home to over ten major groups of organisms like corals, mollusks and

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sponges. Almost all marine life depends directly or indirectly on the microscopic algae that are found only at the surface zones of the seas and oceans. Hence, most of the animals in the oceans live in the sunlit zone. They migrate towards this zone regularly in search of food. Some animals only eat plants. Biological oceanography deals with all the marine life and their migration patterns.

Study of controlling factors The ecology of seas depends on the biotic and abiotic physical and chemical parameters. The nature of sea water, properties of sea water, interaction of sea water with the atmospheric air, the solar radiation and its effects, salinity and density differences in oceanic waters, the wind driven forces and the changing hydrostatic pressure with reference to depth, are the abiotic aspects controlling the ecology of marine environments. The significant roles played by these parameters are studied under biological oceanography.

Solar Radiation Sunlight is the most important parameter for all marine life in the seas. Only a fraction of sunlight can penetrate thought the surface zone and help in carrying out the photosynthesis by plants. The energy is consumed for the conversion of inorganic matter to organic compounds. Some amount of radiation is absorbed by water molecules and converted to heat. This heat controls the temperature variations of the oceans. The depth-wise distribution of plants and animals is also controlled by the penetration of light. There is also a periodic change, as observed in the solar radiation and light penetration. These help the vision in animals, their migration and breeding periods within the sea. Biological processes enacted by sunlight is major aspect in biological oceanography to understand.

Radiation at the surface Solar radiation at the sea surface and the vertical variation in the light intensity are to be measured in proper units. The notable light units used for biological studies of oceans are a) Einstein (E) unit, which measures the Photons and b) Watt (W), which measures the energy of radiation. The energy of radiation depends on the wavelength of the light. Photosynthesis radiation happens between 400 mm and 700 mm. An einstein is a unit defined as the energy in one mole (6.022×1023) of photons. Because energy is inversely proportional to wavelength, the unit is frequency dependent.

Temporal variations About half of the solar energy is absorbed (or) scattered by various layers of the atmosphere. Only 50% of it is reaching the sea surface. In this process, some portion is reflected back to the atmosphere depending upon the angle of incidence. The amount of radiant energy reaching the surface is a function of the sun’s angle of incidence, the length of the day, time of the day, time of the year, the latitude, and the prevailing weather conditions. This is called as temporal variations. The temporal variations of radiation may be a) Diel variation – change that happens between a day and night b) Diurnal variation – change that may occur only during the day time c) Seasonal variation – change that happens between the seasons, especially at high altitudes.

Penetration of light Based on the light intensity and relative penetration of light in the sea, three vertical ecological zones have been identified as: a) Euphotic zone

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b) Disphotic zone and c) .

The shallowest zone is the euphotic zone existing just below the sea surface. In this zone, light penetration fully supports all to grow and reproduce. The respiration loss is also balanced by a compensation depth which marks the lower boundary of Euphotic zone. The dim lighted zone below the euphotic layer is called as the disphotic zone. The last layer which is under complete darkness, where no sunlight can reach, is called as the aphotic zone. Biological oceanography attempts to study all the conditions of these zones.

Factors Controlling Circulation Many marine processes are controlled by the temperature of water. They may be physical, chemical and biological processes. Temperature and salinity of oceanic waters determine the density. Due to this, the vertical water circulation and movements are fully controlled by all these three properties. Exchange of heat happens between ocean and atmosphere continuously. There is also a wide range of temperature variation on the sea surface. It exceeds 300C in tropical oceans, 400C in shallow seas, and as low as – 1.90C in Polar Regions. Oceans are cooled by evaporation. A good amount of heat is transferred during this transformation of water into water vapor.

Classification of zones with temperature variations Ocean surface temperature fluctuates with reference to days, months, seasons and years. It also varies with reference to Polar, tropical, subtropical and temperate zones of the globe. The surface turbulent waters also transfer heat downwards. Due to this, the uppermost part of Oceanic water has a relatively raised temperature. This gets decreased at a depth of 200 to 300m and upto 1000m.

The water layer showing the steepest temperature gradient is known as . The zone showing the rapid changes in density of water is known as . Pycnoline acts like a barrier to vertical water circulations, and also animal movement. At 2000 – 3000m depth, the oceanic water temperature never rises above 40C. It also goes down upto 00C to 30C in deeper zones. Biological Oceanography becomes an interesting subject when we start studying these deep water horizons.

Seawater is unique Seawater is a Unique water. It contains more dissolved salts than river water, lake water and rain water. The salinity is expressed in terms of total dissolved inorganic ions and other compounds and gases. The average salinity of the ocean water is 35 ppt. When surface water gets evaporated, the salinity is increased. It happens at the ocean surface. The Salinity gets lowered due to rainfall, river water inflow and after every snow melts, in the waters of seas and oceans.

Vertical variation in salinity Vertical variation of salinity is an important limiting factor for the marine life to survive. The layer at which a rapid change in salinity occurs is known as . Salinity varies with reference to seasons, depth and locations. Marine life has unique physiological mechanisms to cope up with this salinity variations. Osmoregulation is one of the essential mechanisms. The marine life is also classified based on their tolerance level of salinity. The species which can tolerate a wide range of salinity are called Euryhaline and those which can tolerate a narrow range of salinity are called as Stenohaline species.

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Density of Ocean Waters The density of seawater depends mainly on the salinity and temperature and to some extent by its hydrostatic pressure. When salinity increases, density also increases. The movement of water masses, in the oceans, are controlled by all these 3 parameters. Horizontal water movement is controlled by wind, temperature and Salinity. The Vertical movement of water is controlled by temperature, salinity and density.

The normal density of Seawater at the surface level is very low. When it increases, the water mass sinks down below and reaches the appropriate strata of matching density. The sinking of water is called as downwelling and upward movement of water is called as upwelling. Advection is the term used for horizontal and vertical movements of water in these water bodies. Biological oceanography attempts to analyse all these aspects as well.

Pressure in ocean water The hydrostatic pressure of oceanic water column is determined by the equation Sgh, where g is the acceleration due to gravity,S is the density of water and H is the thickness of water column. Pressure increases due to weight of overlying mass. It is expressed in Newtons per Sq. metre. At 10m depth, the pressure will be ten to the power of five Newtons per meter square ( 105 Nm-2 ). This is equal to 1 bar (or) 1 atomosphere. Hence, the depth wise variation in pressure is calculated based on this range.

All marine life existing within the deep oceans are subjected to very high pressures. The pressures may go upto 1000 atmosphere in the deep ocean basins. Some animals may travel up and down for several hundred metres and experience this change. Both pelagic and benthic species do inhabit these pressure changes. They are called as eurybathic species. The marine life which cannot tolerate such pressure variations are called as stenobathic species. Study of Biological oceanography becomes more interesting while dealing with all these aspects.

Surface Water Currents Ocean water surface currents are generated by the winds. These water movements influence the biological productivity and nutrient availability. Due to this, the geographical distribution patterns of pelagic and benthic marine species are also varied. Ocean surface currents are fully controlled by global wind systems. Their directions are modified by the earth’s rotation. Biological oceanography considers all these aspects while analyzing the marine life.

Marine flora Phytoplanktons and are the two major types of planktons existing in the shallow depth water layers of the oceans. Most of the phytoplanktons are unicellular algae. They also include diatoms, green algae, yellow-green algae, blue green algae, red algae, silicoflagellates and dinoflagellates. In addition, Cryptomonads, Prasinomonads, Chloromonads and Chrysomonads are the other marine phytoplanktons predominantly seen in the seas and oceans. These are present throughout the lighted layers of the oceans. Phytoplaktons are the major primary producers in the pelagic zone. The rate of in plant mass is called as Primary Productivity. The total weight of all organisms in a given area (or) volume is known as the biomass.

Controls of Primary productivity

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The Physical controls of Primary Production are very essential factors. The properties that are controlling the primary production in oceanic shallow waters are Light, Physical forces, Abundance of nutrients and temperature. It also varies with reference to seasons, depth and location.

Marine fauna Marine animals are divided into 3 groups as , and . Zooplankton are the drifting animals and are usually small but grow to fairly large size. Typical example is a Jellyfish. The zooplankton population includes some members like eggs or larval forms of organisms which may grow up and leave the planktonic community to join the nekton or benthos.

Pelagic organisms Pelagic organisms are classified into various types based Virio Plankton – 0.02-0.2mm – Femto plankton Bacterio Plankton - 0.2 -2.0 mm – Pico plankton Myco plankton - 2.0-20.0 mm – Nano plankton Phyto plankton - 20-200 mm – Micro plankton Protozoo plankton - 20-200 mm – Micro plankton Metazoo plankton - 0.2 -20 mm Meso plankton - 2.0 to 20 cm Macro plankton - 20-200 cm – Mega plankton

A bucket of seawater might hold a million microscopic diatoms which are relatives of sea weeds encased in glassy boxes. To grow, need nutrients from the seawater and lots of sunlight. The large quantities of diatoms and phytoplankton give a color to the sea water.

General types of plants There are two general types of plants found in the ocean. They are those having roots that are attached to the ocean bottom and those that are not having roots which simply drift about with water. The rooted plants are only found in shallow water because of the availability of sunlight for photosynthesis. The most abundant plants in the ocean are the phyto planktons. These are usually single-celled, minute floating plants that drift throughout the surface of the oceans.

The word Plankton means wandering or drifting in Greek. Planktons are floating plants or organisms. There may be Phytoplanktons denoting plants and Zooplankton denoting the animals. Planktons are mostly microscopic dimension. Nektons are free-swimming animals. Some of the Phytoplanktons are passively transported by the currents in the sea. Fish, and marine mammals are the major Nektons, of oceans.

Nektons are the free swimmers and the largest portion of familiar population of animals found in the oceans. Common , , , eels and squid are all examples of nekton. Whales, Sea mammals, dolphin and porpoise codfish/trout. The third type of sea animals spend their entire life on or in the ocean bottom. This group of marine animals is called benthos. Lobsters, , various norms, snails, oysters, etc.

All marine life need food. Plants make their own food but animals obtain food from their environment. A food chain represents the transfer of body-building substances and energy when one organism eats another. Diatoms form the first link in the marine food chain. In the ocean, there are

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innumerable individual food chains overlapping and intersecting to form complex food webs. Most marine creatures eat a variety of foods. The rich diversity of life in the sea forms a delicately balanced. Network of predators and prey. All organisms are dependent on one another for survival.

Marine zooplanktons Marine Zooplanktons animals range from microscopic unicellular organisms to jellyfish size which are several metres in diameter. They are of two kinds as a) Holoplankton (Permanent Planktons-Spend their entire life cycle in water column) and b) Meroplankton (Temporary residents of Plankton community) Planktons show vertical migration within every 24 hours. This is called as diel vertical migration. This occurs in many epipelagic and mesopelagic species.

Holoplanktons. There are about 5000 species of holoplanktons existing in seawaters. Many notable ones are Foraminifers, Radiolarians, Ciliates, Tintinnids, Jellyfish, Cnidarians , Ctenophores, arrow worms, some heteropods, Pteropods Copepods, Ostrocods, Amphipods, Euphansiids, Mysids, Decapods and Salps.

Meroplantons. The Meroplanktons are miniature adults spending a few minutes to several months and years in the upper layers. Most of them are larvae of benthic forms. They include Snail religers, starfish, sea urchins, barnacles and crabs.

Migration of marine animals Marine Zooplanktons show three kinds of patterns as: a) Nocturnal migration - after sunset b) Twilight migration - rising up at sunrise c) Reverse migration - surface rise during the day and descent to depths at nights. There are also seasonal vertical migrations happening in the shallow waters for marine life. Zoogeographic studies help understanding the distributions of living organisms and the physiological or ecological reasons behind these mobilities. Long –term observations show that plankton abundance and species composition may change with reference to time, climatic variations, and nutrient availability.

Properties affecting marine life. Properties affecting the marine life are many. The following are the properties affecting life in the seas and oceans: 1. Quality of sea water 2. Skeleton shape and size of organisms 3. Buoyancy 4. Gravity 5. Temperature of ocean water 6. Density 7. Light 8. Availability of Nutrients

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9. Water turbulence and 10. Hydrostatic pressure.

Aspects of Biological oceanography In addition to these, biological oceanography deals with the study of 1. Migration 2. Zoogeography 3. Energy Flow & Mineral Cycles 4. Mineral cycles 5. Marine mammals/ Sea birds / Marine Fish-Fish migrations 6. Fisheries –world Fish catch/ Mariculture 7. Coral Reefs- 8. Human Impacts on Marine Biotic 9. Marine Pollutants a. Petroleum Hydrocarbon b. Plastics c. Pesticides d. Heavy metals e. Sewage f. Radioactive wastes g. Thermal effluents.

Conclusion About 2% of the total human food consumption comes from the marine species. The economic utilization of marine natural resources is very high. Biological oceanography is an inter-disciplinary science. Hence, biological oceanography is a rapidly developing field of marine sciences and Earth sciences.

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