The sea is the most obvious feature of the earth’s surface.
Approximately seventy percent of this surface is covered by water, in one way or
another. Beneath this water are the familiar sands of the beaches, bottoms of
bays, and the inshore ocean. Farther offshore this water covers an amazing
submarine topography of underwater canyons, trenches, mountains, and plains.
Unlike the continents, which are physically separated from one another, the
oceans are continuous and interconnected. Since the “world ocean is
continuous”(M.J. Keen) it has similar characteristics throughout. In the early
1870s oceanographers collected seawater samples from all of the seas of the
world at a variety of depths. When analyzed, the samples were found to have
quite similar characteristics. These findings convinced many that a method of
study was needed. The study of oceans was named oceanography.
Density, salinity, and temperature are very important concepts in the
study of oceanography. The salinity and temperature of the water influence its
density, and the differences in density are the major factor in understanding
the formation of currents and the positions of water masses in the sea. In
addition, temperature and salinity play major roles in influencing the
distribution of plants and animals.
The sediments of the sea floor may be divided into lithogenous,
hydrogenous, biogenous, and cosmogenous sediments. Lithogenous sediments are
the major sediments on the ocean floor. They are derived from the chemical and
mechanical weathering of rocks. Biogenous sediments are composed primarily of
the protective outter covering of small marine animals and plants. If these
remains comprise at least thirty percent of the sediment it is called an “ooze”.
“Oozes” were named for the types of organisms that formed them. Hydrogenous
sediments form as a result of the chemical reactions that occur in the seawater.
These reactions result in the formation of small particles, which are deposited
on the sea floor. Currents move these particles and cause them to collide with
the other particles. If many of these collisions occur they may form nodules.
Nodules are found on some portions of the deep-sea floor. The sediment type
frequently determines the type of organisms that will be found in that specific
“Waves are variable and transitory features of the sea’s surface.”
(Sandra Smith) All waves, from the smallest ripple to the most destructive
tsunami, have common characteristics. They all have crests, troughs, wave
heights, lengths, and periods. Also, water particles that make up the waves all
move in identical orbital patterns. The orbital pattern is up and forward in
the crest and down and back in the trough. It is only when the wave becomes
unstable that the orbital motion is destroyed. The water particles then begin
to move at the same speed as the moving wave form.
Breaking waves release a tremendous amount of stored energy on a beach
face. This energy moves the sand about and changes the configuration of the
bottom. As the bottom configuration is changed by the waves, it changes the
characteristics of incoming waves. This interaction between the waves and the
bottom results in the beach face having an everlasting wave pattern.
Everything in the universe is composed of extremely small paritcles
called atoms, which are often bonded together to form molecules. Molecules are
formed as the result fo the transfer of electrons between atoms. The complete
loss and gain of electrons results in the formation of ionic molecules, which
have completely positive and negative vegions. Unequal sharing of electrons, on
the other hand, characterizes the polar covalent molecules, which have only
partially positive and negative regions. The equal sharing of electrons result
in the formation of nonpolar covalent molecules, which do not develop charged
Due to the development of charges on ionic and polar molecules,
intermolecular attractive forces form between these molecules, intermolecular
attractive forces form between these molecules and enable the compounds to exist
in the solid and liquid state. Ionic compounds have long-range order and exist
as solids. Polar covalent molecules are liquids because of their short-range
order, while the nonpolar gases do not develop intermolecular attractions and as
a result exibit no order.
Changes in state are due to a change in the order of compounds. When
energy is added, molecular motion increases and intermolecular attractive forces
are disrupted. This results in the melting of solidsand the evaporation of
liquids. When energy is removed, the molecular motion is decreased, which
increases the formation of intermolecular attractive forces. This allows vapors
to condense as liquids to freeze.
The physical and chemical components of water interact with and affect
the plant and animal life in the sea. The plants, animals, and bacteria that
inhabit a given marine area continually react with, change, and are changed by
the total biotic and abiotic environment. Light plays a vital role in the sea,
since the producers require sunlight as the energy source to convert the low-
energy simple plant nutrients into the more complex high-energy molecules that
can be used by the consumers. The dominant plants of the sea are the
microscopic phytoplankton, while copepods. The copepods are important, since
they provide the major link in the transfer of energy from the phytoplankton to
the large animals of the sea.
Density exerts profound effects on both the biotic and abiotic
components of the sea. Many marine forms, both animal and plant, have developed
unique life-styles of seawater. In addition, density barriers are formed in the
sea in response to temperature and salinity differences between water masses.
In many cases these density barriers trap nutrients below the euphotic zone and
make them spatially unavailable to the plants in these areas. This is the case
in the tropical seas, as well as in all of the world’s deep oceans, where the
density barriers are permanent.
Plant nutrients tend to cycle throughout marine systems, from their
simple, low-energy, dissolved forms to plants, animals, and then to bacteria.
When considering the cycling of nutrients through any system, it is important to
remember that metter and energy are inter-changeable. Cycles that encompass
both the biotic and abiotic components of a system are called biogeochemical
Biochemical cycles involve the transfer of the essential, minor, and
trace elements from the abiotic to the biotic components of a system.
The transfer of food is extremely important in marine life. The
transfer of food energy may be depicted by food chains and food webs. Food
chains can be and generally are unstable, since the loss of a single link can
have drastic effects on the remainder of the chain. Food webs are more stable,
since a variety of alternate food sources exist at each trophic level.
Wind-drift currents are formed by wind moving across the surface of the
sea and setting water in motion. Winds are formed by the warning and cooling
affects the density of the air, causing it to move into adjacent air masses.
Once in motion, both air and water masses are influenced by the rotation of the
earth. This causes the water masses to appear to deflect to their right in the
Northern Hemisphere and to their left in the Southern Hemisphere. As a result,
the major wind currents appear to travel in large figure eights from the equator
northward and southward.
Density currents involve a large percent of the sea’s volume. Since
these currents are the result of temperature and salinity differentials that
develop between adjacent water masses, they are often called thermohaline
The thermohaline circulation travels through the subsurface waters of
all of the world’s oceans. These currents carry oxygen to the a ysphotic zone,
where because of the absence of light, photosynthesis can not occur. They also
remove large amounts of nutrients from the euphotic zone and transport them for
great distances throughout the deep ocean.
The current patterns in estuaries are also generally formed in response
to density differentials. Depending on the amount of marine and fresh water
that enters these systems, estuaries may be highly or moderately stratified,
vertically homogeneous, or hepersaline. The resultant salinity variations in
these areas has a direct influence on the biotic distributions in estuaries.
Shorelines are the point of contact between the marine and terrestrial
environments and, as such, are flooded at high tide and exposed at low tide.
They are only a part of the coastline or coastal zone, inland and for hundreds
of miles along a shoreline. Shorelines are constantly changing.
Coastal sediments are continually attacked and reworked by the sea.
Waves move these sediments into the surf zone, where they are picked up and
transported by the the long-shore current. Those sediments are sorted by this
currentand eventually deposited to form such major coastal features as barrier
islands and sand splits. Inlets form, migrate, close, and reform along barrier
beaches. A combination of inlet fromation, closure, and the overwash of a
barrier beach during storms causes the barrier island to migrate towards land.
Estuaries are also major coastal features. They form in a variety of
ways. They may form behind a barrier island, sand spit, sea island, or other
such feature or be formed by the tectonic movements of isostatic adjustments of
the earth’s crust. Others are formed directly by glacial activity. Estuaries
are called a variety of names, including bays, sounds, and lagoons. These are
the most common, but regardless they are all semi-enclosed bodies of water with
one or more free connections with the sea.
The construction of groins, jetties and breakwaters is often harmful and
tend to cause of increase erosion. All coastlines are extremely dynamic areas
that are interrelated by the longshore currnet. Although these areas must be
treated as units, since what occurs along the way will be reflected by beach
conditions down the current.
The coastal zone provides an unrivaled opportunity to observe ecological
relationships. The sea, offshore the inner neritic zone, is remarkable in its
constancy. In any given area, the salinity and temperature are virtually
invariable. Pressure is constant, but no other environment are the organisms
sujected to such tremendous pressures.
The vast majority of the palagic and benthic realms are in perpetual
darkness, and effective photosynthesis does not occur. All the organisms of the
open ocean are then dependent on the small portion of the sea that is in the
euphotic zone. As a consequence, the animal life is sparce, and different food
chains develop. In the deep ocean much of the initial energy is thought to be
provided by the bacteria, which like the phytoplankton of the euphotic zone,
serves as a food source for the grazers.
The second law of thermodynamics, in conjunction with the small area
that is actuall inhabited by the producers, shows the fallacy of relying on the
sea as a food supply. It this becomes a reality due to over-population, it will
be necessary to feed at a trophic level much closer to the energy source.
Coral reefs are one of the most beautiful and exciting phenomena in the
oceans. The coral reef is a biological community consisting of the coral itself
and a variey of small animals and plants, of which algae is as abundant as the
coral. The framework, or base, of the reef is formed by the skeleton of dead
coral animals, with the living corals and algae at the top of the reef. As the
kinds of reef that grow at sea level have to be solid enough to withstand the
battering of the waves, framework must be strong. Many fish and other animals
and plants live on or in reefs, and all this life forms a rich, varied and
Coral reefs occur in warm, tropical oceans where the temperature is
higher than sixty-eight degrees farenhiet. They need sunlight in order to grow,
so they only grow in clear shallow water down to depths of not much more than a
hundred feet. Reefs also need a good circulation of sea water to bring them
oxygen and food, so strong wave action is beneficial to them.
Coral is an animal which reproduces very quickly by splitting, to form
colonies of coral. Each animal has a chalky skeleton which is joined to
neighboring skeletons, forming the strong framework of the reef. In some coral
colonies, such as brain coral, it is impossible to see each individual animal;
but in other colonies, the skeleton of each animal can be seen.
Coral feed on zooplankton. However, the microscopic plants that live
within the coral also supply it with food and reef-building materials. The
plant in return seemed to benefit from the coral, gaining shelter and food
materials from it.
There are three main types of coral reefs: the fringing reef, the
barrier reef, and the atoll. Conditions on reefs vary from the breaking surf of
the sea edge to the quieter lagoon. The fringing reef grows out from an island,
or other land form, but is still attached to it. An example of fringing reefs
are the reefs bordering the Florida Keys. A barrier reef is separated from the
island or mainland, and may be a few miles distant. The Great Barrier reef is
over a thousand miles long, forming an off-shore break-water for the east coast
of Australia. An atoll is a circular surrounding a lagoon, often not associated
with any obvious land. Atolls occur mainly in the Pacific and Indian Oceans,
rising abruptly from the deep seas.
A few centuries ago scientist were puzzled to find coral atolls in the
deep oceans with no land visible because they knew that the corals could only
grow in shallow. The naturalist Charles Darwin during his voyage on HMS Begal
from 1831 to 1836, examined the number of atolls and put forth a theory for
their formation. He suggested that a volcanic or seamount provided a shallow
water base for the growth of the fringing reef. This island would be eroded by
the waves and would sink slowly under its own weight. To remain in shallow
water, the corals of the reef would grow upward as the island sank until the
reef became separated from the island by a donut-shaped lagoon, forming a kind
of barrier reef. Further sinking of the island below the sea surface would
leave only the reef as an atoll, the island being no longer visible.
Darwin’s theory was not proven correct until 1952, when holes were
drilled into Eniwetok Atoll in the Pacific Ocean. After drilling through almost
a mile of coral, the scientist reached the old volcano. It had been sinking for
some 60 million years and all this time the coral had been growing upward
keeping pace with the sinking island.
The reproduction of coral is very interesting. During the reproduction
stage of the coral, the animal itself is stationed. First and foremost, the
part of the coral that is actually doing the reproducting is called the polyp.
Polyps reproduce in two different ways. One is by eggs, and the other is by a
process called budding. When the egg is fertilezed by sperm, the egg develops
into a tiny larcal organism called a planulae. The planulae settles on the
ocean bottom. The planule lands on whatever the currents allow it to. It will
most likely end up on a rock, or on another coral. Eventually the planulae
develops into a polyp. Each polyp builds a limestone skeleton which is
attached to the surface of which the poyp has landed on, which can be either a
rock or another coral. After the coral establishes itself, the upper part of
the body becomes dome-shapes and develops a stomach and a mouth.
Tentacles form around the mouth. The tentacles are used to draw food in
from the surrounding waters of the oceans. the tentacles of teh coral are armed
with special stinging structures. Those special stinging structures are called
nematosysts. The tentacle’s nematocysts paralyzes th etiny prey that the coral
eats. The coral’s major food are small marine organisms.
In recent years, outbreaks of cholera, typhoid, and viral hepatitis in
Latin America, the Mediterranean and Southeast Asia have all been traced to
contaminated seafood. It is because of the discharge of sewage and polution
directly into coastal waters. Industrial wastes have been dumped in the oceans
of our world. They contain a mixture of chemicals, such lubricating oils, zinc,
copper, bleaching agents, and strong acids & alkalis. These chemicals are
extremely toxic to marine organisms.
There is strong need for international action to control marine
contamination and pollution. Pollution is now the subject of numerous regional
and international agreements. Conventions regulating the discarge of oil from
ships, and the development of emergency response systems to oil pollution
accidents have contributed to the decline of ship-based souces of oil pollution
over the last two decades. The moratorium on dumping of radioactive waste at
sea under the London Dumping Convention also represents another response to
concerns about the risks posed by such diposal. Some regions have concluded
agreement which ban dumping of any radioactive waste at sea. In the
Mediterranean and Red Sea, all discharge of oily wasted from ships is also
The differences between terrestial regions are well known. Less well
known are the features that distingush the Atlantic from the Pacific Ocean, or
the coast of South America from those of Southern Africa. Regardless of this,
the various regions of the world’s oceans are all affected by human activity,
with pollution and harvesting of resouces of resouces being common to all seas
and oceans. The various marine resources, as well as the extent of human
impacts on them, are examined region by region, illustrating hos stresses on the
marine environmet treatened the very resistance of some habitats and species.