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 sea expeditions conducted by the people from 15th to 16th centuries. Through Ocean explorations people conducted detailed underwater surveys and mapped the ocean floors with respect to their physical features, chemistry and biological conditions.

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Topic of the lesson
BIOLOGICAL OCEANOGRAPHY
Biological OceanographyBiological Oceanography
By
Prof.A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore, India

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Table of Contents

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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 marine life, their ecological
conditions, distribution controls and the various
interactive mechanisms of marine life will be
understood in this lesson.
Objectives

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 Seas and Oceans 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.
Introduction to Marine environment
(…Contd)

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 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.
Introduction to Marine environment

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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.
(…Contd)

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 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.
The First Texts of Oceanography
(…Contd)

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 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.
The First Texts of Oceanography

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 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.
Historical development
(…Contd)

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 His Nephew, James Ross, during 1839-43, collected
the samples of benthic animals as deep as 730 m, and
gave a lot of 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.
Historical development

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Component of marine environment
 Marine ecosystems are characterized by both biotic
and abiotic components.
The dominant biotic components are
 organisms and their species,
 predators,
 parasites,
 competitors and mates.
(…Contd)

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 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.
Component of marine environment
(…Contd)

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 Marine ecosystems are typical environments ranging
from a small tidal inlet to the deep water ocean
basins.
 Depth of water column is a major factor in addition
to its movement and circulation.
 Solar and atmospheric interactions are very
important aspects in the biological oceanography.
Component of marine environment

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 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.
Conditions of marine environment
(…Contd)

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 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 environment

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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.
(…Contd)

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 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.
Conditions of Marine Life

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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.
Temperature and light penetration
(…Contd)

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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.
Temperature and light penetration
(…Contd)

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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.
Temperature and light penetration
(…Contd)

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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.
Temperature and light penetration
(…Contd)

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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.
Temperature and light penetration

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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.
Classification of Marine zones
(…Contd)

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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.
Classification of Marine zones

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Pelagic zone
 The Pelagic zone 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 200 m down from the ocean surface.
(…Contd)

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 The Mesopelagic zone 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 6000 m from the
oceanic surfaces.
Pelagic zone
(…Contd)

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 The Hadal Pelagic zone is the zone of deep water
extending beyond 6000 m 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.
Pelagic zone

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 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.
Benthic zone
(…Contd)

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 The Sub littoral zone refers to the zone of low tide
water line to 200 m depth on the continental shelf
region inside the sea.
 The Bathyal zone is the zone ranging from 200 m to
3000 m depth of water column inside the sea.
 The Abyssal zone is ranging from 2000 m to 6000 m
depth inside the sea and it exists mostly on the
continental slope regions.
Benthic zone
(…Contd)

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 The Hadal zone 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.
Benthic zone

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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.
(…Contd)

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 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 1000 m and 4000 m depth
below the sea surface, where there is no penetration of
light.
Ecology of seas
(…Contd)

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 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.
Ecology of seas

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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.
(…Contd)

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Life in oceans
 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 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.
(…Contd)

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 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.
Life in oceans

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 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,
Study of controlling factors
(…Contd)

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 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.
Study of controlling factors

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 Sunlight is the most important parameter for all marine life
in the seas.
 Only a fraction of sunlight can penetrate through 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.
Solar Radiation
(…Contd)

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 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.
Solar Radiation

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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.
(…Contd)

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 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.
Radiation at the surface

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 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
Temporal variations
(…Contd)

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Temporal variations
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.
(…Contd)

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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.
Temporal variations

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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
b)Disphotic zone and
c) Aphotic zone.
(…Contd)

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 The shallowest zone is the euphotic zone existing just
below the sea surface.
 In this zone, light penetration fully supports all
phytoplankton to grow and reproduce.
 The respiration loss is also balanced by a compensation
depth which marks the lower boundary of Euphotic
zone.
Penetration of light
(…Contd)

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 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.
Penetration of light

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 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.
Factors Controlling Circulation
(…Contd)

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 Exchange of heat happens between ocean and atmosphere
continuously.
 There is also a wide range of temperature variation on the
sea surface.
 It exceeds 300
C in tropical oceans, 400
C in shallow seas,
and as low as – 1.90
C in Polar Regions.
 Oceans are cooled by evaporation.
 A good amount of heat is transferred during this
transformation of water into water vapor.
Factors Controlling Circulation

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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 300 m and upto 1000 m.
(…Contd)

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 The water layer showing the steepest temperature
gradient is known as thermocline.
 The zone showing the rapid changes in density of
water is known as Pycnocline.
 Pycnoline acts like a barrier to vertical water
circulations, and also animal movement.
Classification of zones with temperature variations
(…Contd)

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 At 2000 – 3000m depth, the oceanic water
temperature never rises above 40
C.
 It also goes down upto 00
C to 30
C in deeper zones.
 Biological Oceanography becomes an interesting
subject when we start studying these deep water
horizons.
Classification of zones with temperature variations

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Sea water 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.
Sea water is Unique
(…Contd)

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 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.
Sea water is Unique

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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 Halocline.
 Salinity varies with reference to seasons, depth and
locations.
 Marine life has unique physiological mechanisms to
cope up with this salinity variations.
(…Contd)

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 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.
Vertical variation in salinity

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 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.
Density of Ocean Waters
(…Contd)

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Density of Ocean Waters
 The normal density of Sea water 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 down welling
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 analyze all these
aspects as well.

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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.
(…Contd)

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 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 atmosphere.
 Hence, the depth wise variation in pressure is
calculated based on this range.
(…Contd)
Pressure in Ocean Water

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 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.
(…Contd)
Pressure in Ocean Water

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 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.
Pressure in Ocean Water

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 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.
Surface Water Currents
(…Contd)

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 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.
Surface Water Currents

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Marine Flora and Fauna
 Phytoplankton and Zooplanktons are the two major
types of planktons existing in the shallow depth water
layers of the oceans.
 Most of the phytoplankton are unicellular algae.
 They also include diatoms, green algae, yellow-green
algae, blue green algae, red algae, silicoflagellates and
dinoflagellates.
Marine FloraMarine Flora
(…Contd)

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 In addition, Cryptomonads, Prasinomonad, Chloromonads and
Chrysomonads are the other marine phytoplankton
predominantly seen in the seas and oceans.
 These are present throughout the lighted layers of the oceans.
Phytoplakton are the major primary producers in the pelagic
zone.
 The rate of primary production 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.
Marine Flora

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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.
Controls of Primary productivity

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 Marine animals are divided into 3 groups as Zooplankton,
Nekton and Benthos.
 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
fish eggs or larval forms of organisms which may grow up
and leave the planktonic community to join the nekton or
benthos.
Marine fauna

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Pelagic organisms
Pelagic organisms are classified into various types
 Virio Plankton 0.02-0.2 mm – 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
(…Contd)

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

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 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.
General types of plants
(…Contd)

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 The most abundant plants in the ocean are the
phytoplankton.
 These are usually single-celled, minute floating
plants that drift throughout the surface of the
oceans.
General types of plants
(…Contd)

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 The word Plankton means wandering or drifting in
Greek.
 Planktons are floating plants or organisms.
 There may be Phytoplankton denoting plants and
Zooplankton denoting the animals.
 Planktons are mostly microscopic dimension.
General types of plants
(…Contd)

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 Nektons are free-swimming animals.
 Some of the Phytoplankton are passively
transported by the currents in the sea.
 Fish, squid and marine mammals are the major
Nektons, of oceans.
General types of plants
(…Contd)

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 Nektons are the free swimmers and the largest
portion of familiar population of animals found in the
ocean.
 Common fishes, octopus, whales, eels and squid are
all examples of nekton.
 Whales, Sea mammals, dolphin and porpoise
codfish/trout.
General types of plants
(…Contd)

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 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, starfish, various norms, snails, oysters,
etc.
General types of plants
(…Contd)

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 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.
General types of plants
(…Contd)

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 In the ocean, there are 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.
General types of plants

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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)
(…Contd)

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 Planktons show vertical migration within every 24
hours.
 This is called as diel vertical migration.
 This occurs in many epipelagic and mesopelagic
species.
Marine Zooplanktons

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Holoplankton
There are about 5000 species of holoplankton existing in sea
waters. Many notable ones are

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 The Meroplankton 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.
Meroplanton

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Marine Zooplanktons show three kinds of patterns as:
 Nocturnal migration - after sunset
 Twilight migration - rising up at sunrise
 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.
Migration of marine animals
(…Contd)

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 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, stratification and nutrient
availability.
Migration of marine animals

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Properties affecting marine life
 Properties affecting the marine life are many.
The following are the properties affecting life in the seas and
oceans:

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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
Aspects of Biological oceanography
(…Contd)

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9. Marine Pollutants
 Petroleum Hydrocarbon
 Plastics
 Pesticides
 Heavy metals
 Sewage
 Radioactive wastes
 Thermal effluents.
Aspects of Biological oceanography

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 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.
Conclusion

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Thank You