Lesson Outline

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Lesson Outline
I. Biomass and Primary Production
II. Phytoplankton Adaptations
III. Adaptations to Saltwater Environments IV.
The Distribution of Marine Life
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Ecology
Ecology is the branch of science that examines
the interactions of populations with each other
and with their physical and chemical
environments.
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Primary Production

• Biologists refer to the amount of autotroph
  tissue in the ocean at a particular moment in
  time as its biomass, often measured in gC/m3.

The rate at which new autotroph tissue is being
produced by photosynthesis (in gC/m3/time) is
called primary production, because this
production is the start of most marine food
chains.
Gross primary production is the rate at which
organic carbon is produced by photosynthesis.
Net primary production is the rate at which
organic carbon is produced after accounting for
respiration losses.
Net primary production determines how much energy
is available for the fish and other animals up
the food chain.
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Measuring Primary Productivity and Biomass

• There are a number of methods used to measure
  primary production and biomass

1. The Light/Dark Bottle Method
2. The Carbon-14 (14C) Method
3. Fluorescence
4. Ocean Surface Color
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The Light/Dark Bottle Method

• Samples of sea water, containing both phyto- and
  zoo-plankton, are collected from a series of
  depths.

The oxygen level is measured, each sample is
divided into light and dark bottles, and the
bottles returned to depth for 10-12 hours of
daylight.
At the end of that time, the bottles are
retrieved and the amount of oxygen in each bottle
measured.
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The Light/Dark Bottle Method

• The oxygen gain in the light bottle is the net
  result of photosynthesis and respiration.

The oxygen decline in the dark bottle is the
result of respiration.
The gross oxygen production is the sum of the net
production (light bottle) and the respiration
(dark bottle).
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The Light/Dark Bottle Method

• The photosynthesis equation is then applied to
  determine the corresponding amount of biomass
  produced (one glucose molecule is created for
  every six oxygen molecules released) during the
  experiment.

The light and dark bottle method measures gross
primary production, the total amount of sugar
produced during daylight hours.
This is not the amount of food available for the
fish on up the food chain, however, because the
autotroph must use some of this sugar for its own
metabolic needs especially the following night.
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14C Method

• Net primary production is measured by the
  carbon-14 method.

Samples of sea water, containing both phyto- and
zoo-plankton, are again collected from a series
of depths.
The sample is divided into light and dark
bottles, a small amount of bicarbonate ion
(HCO3) containing radioactive 14C is added to
each, and the bottles returned to depth for 10-12
hours.
The phytoplankton uptake both forms of carbon in
the production of new sugar molecules.
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14C Method

• After retrieving the samples, the contents of
  each bottle are poured through a filter, trapping
  the plankton on the filter pad.

A Geiger counter then measures the radioactivity
of filtered biomass, and a straight-forward
calculation converts the radioactivity to the
amount of biomass produced.
The disadvantages of the carbon-14 method are
that it requires the use of more sophisticated
and expensive equipment, radiation safety must be
observed, and waste disposal can be problematic.
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An Application of the 14C Method

• NOAAs Long Line cruise N93S took place aboard
  the research vessel R/V Malcolm Baldrige between
  July 7 August 28, 1993.

Scientists used the 14C method to measure primary
production along a N-S transect of the N Atlantic.
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Measuring Fluorescence

• Because autotrophs contain chlorophyll pigment,
  the autotroph biomass contained in a sample of
  sea water is often measured by determining the
  concentration of chlorophyll in the sample.

When chlorophyll is exposed to a certain
wavelength of UV light, is responds by emitting
(fluorescing) a wavelength of red light.
A device called a fluorometer measures the
fluorescence of a given sample of sea water and
calculates the concentration of chlorophyll.
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Measuring Fluorescence

• The advantage of this method is that a
  fluorometer can give continuous readings from the
  surface to the bottom, or can be towed alongside
  a research vessel to give biomass measurements
  over a broad area.

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Ocean Surface Color

• An instrument known as a Coastal Zone Color
  Scanner (CZCS), mounted on a satellite or an
  aircraft, measures the light energy reflected
  from the ocean surface in four visible
  wavelengths, blue, green, yellow, and red.

The relative intensity of light in these bands is
used to calculate the amount of chlorophyll in
the ocean surface layer.
This method gives broad estimates of biomass over
entire ocean basins.
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Primary Producers in the Sea

• The single cell producers in the sea are mostly
  algae. Most algae are microscopic, but some are
  large enough to see without magnification.

Algae are subdivided into two groups, the
phytoplankton and the benthic algae.
The phytoplankton are the planktonic producers
they live in the upper part of the water column
and must drift with the ocean currents.
The benthic algae live on the bottom, so are
found in coastal waters.
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Spermatophytes

• The other types of producers in the seas are a
  few species of land plants that have returned to
  the sea, called spermatophytes, or flowering
  plants.

The flowering plants are benthic and live only in
shallow coastal water where light is abundant.
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Phytoplankton Adaptations

• Phytoplankton have evolved five adaptations for
  remaining in the photic zone swimming, positive
  buoyancy, spines and projections, curved body and
  formation of chains.

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Physical Restraints on Sinking

• There are two physical processes that also deter
  phytoplankton from sinking below the photic zone.

The first is density stratification.
In summer months, the sun warms the surface ocean
waters, creating a lens of warm water overlying a
layer of denser cold water.
The plants will sink to the interface between the
layers, but are trapped there until the surface
waters are stirred by winds.
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Langmuir Circulation

• A second process is a form vertical water
  circulation in what is known as Langmuir cells.

When the wind blows across the surface of the
sea, it sets in motion a series of circulation
cells that move at right angles to the wind
direction.
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Langmuir Circulation

• As long as the wind continues to blow, these
  circulation cells will prevent most of the
  phytoplankton from sinking below the photic zone.

In most areas of the open sea, the wind blows
steadily but there are a few regions where the
wind is calm for long periods of time.
In these areas, the phytoplankton must be able to
swim or produce oil to remain in the photic zone.
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Food Chains

• Organisms in the sea are often categorized by
  where they fit in different types of food chains.
  

In a grazer food chain, animals consume live
phytoplankton, like a copepod eating a live
diatom.

• common in offshore waters.

Another type of food chain is called the detritus
food chain, in which animals consume dead plants.

• common in coastal waters and estuaries like Tampa
  Bay.

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Chemosynthesis

• In a few isolated parts of the sea, geothermal
  heat in the sea floor creates thermal vents,
  places where seawater has seeped down into the
  sea floor until it encountered hot volcanic rock.
  

The heated seawater convects back up to the sea
floor and boils up like a hot spring.
Living around these thermal vents are populations
of bacteria that use sulfur chemicals to
synthesize high-energy organic bonds, much the
way green plants use light energy, through a
process called chemosynthesis.
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Hydrothermal Vent Communities

• These bacteria, the initial link in a deep-sea
  food chain, are then consumed by a variety of
  benthic worms.

The result is a small, highly productive marine
community surrounding thermal vents in waters
5,000 meters deep.
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Cold Seep Communities

• There is another type of deep-sea chemosynthetic
  food chain, a number of which have been
  discovered in the Gulf of Mexico.

These surround geological features known as cold
seeps, where oil and methane gas bubble up from
sediment layers beneath the sea floor.
Autotrophic bacteria convert energy from the
methane gas to organic tissue.
The bacteria then support dense populations of
tube worms and clams.
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Saltwater Environments
In the marine environment, organisms must develop
strategies to cope with the salinity of seawater.
Euryhaline organisms are adapted to live in
waters with a wide range of salinities.

• Estuarine fish

Organisms that tolerate only small changes in
salinity are called stenohaline.

• Offshore fish

• Reef dwellers

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Adaptations to Saltwater Environments
The cytoplasm of all living cells contain salts
that are essential to the biochemical reactions
carried out within the cells.
Between the cytoplasm within the tissues of the
organism and the water outside the organism there
is a salinity concentration gradient.
The salinity gradient creates an osmotic
pressure, which nature acts to equalize.
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Osmoregulation
Cell membranes are porous and have many small
openings that permit the cells to exchange
materials with the external environment.

• Small molecules (water, oxygen, CO2) pass through
  easily.

• Large molecules (blood proteins, or sugars)
  cannot pass through the cell membrane.

• Electrically charged ions can be excluded from
  passage.

Due to the cell membrane, the only way to
equalize a salt imbalance is to change salt
concentration inside the cell by osmoregulation,
the passage of water through the membrane.
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Osmoregulation in a Freshwater Fish
A fish living in a freshwater environment is
surrounded by water containing no salt, while the
tissues inside the fish have a low concentration
of salt.
To equalize this imbalance, fresh water passes
through the cell membranes into the fish to lower
the concentration of salt within the cell
tissues.
Freshwater fish have well-developed kidneys to
remove excess water and maintain cell salinity.
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Osmoregulation in a Saltwater Fish
A saltwater fish is surrounded by water that has
a higher salt concentration than inside the cell
tissues of the fish.
To correct this imbalance, fresh water flows out
of the fish to raise the salinity of the cell
tissues.
Saltwater fish constantly face dehydration from
this loss of water and must replace this lost
water by drinking.
Since saltwater fish are constantly losing water
from their cell tissues, they often lose kidney
function.
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Saltwater vs. Freshwater Fish
As a rule, osmoregulation is what limits
freshwater fish to lakes and rivers and saltwater
fish to the sea.
There are some exceptions. Many marine species
of fish are observed in the freshwater springs
along the Florida Gulf Coast.
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Euryhaline Fish
A few species of euryhaline fish can move freely
between the freshwater and saltwater
environments.
Salmon, shad, and some eels are born in
freshwater, develop working kidneys, then migrate
to the sea as adults, where they shut down the
kidney but keep it functional.
Later when they return to freshwater to spawn,
they can restart the kidney to help maintain
osmotic balance.
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Temperature
Marine organisms must also adapt to the
temperature of the surrounding environment.
The same prefixes are used to describe the
temperature tolerance of marine species a
eurythermal fish can tolerate a wide range of
temperatures, while a stenothermal fish cannot.
Offshore and reef organisms are typically
stenothermal.
Shallow waters are more likely to undergo rapid
temperature changes, so inshore species are often
eurythermal.
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The Distribution of Marine Life
The numbers of individual marine organisms
observed in the sea are neither uniform nor
random.
Marine species are often clumped or grouped in
some areas of the ocean and sparse in others.
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Plankton Distribution
The motile phytoplankton can swim. Other species
of phytoplankton are nonmotile.
Since they cannot swim, the nonmotile
phytoplankton will be caught up and distributed
around the edges of the Langmuir cells formed by
the wind. Few plankton would be found in the
center of the cells.
The motile phytoplankton however, would swim to
the depth to where the light is optimum for
photosynthesis.
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Diurnal Migration
In the course of the day, motile phytoplankton
migrate upward and downward in the water column
to remain at the optimum depth for photosynthesis
(as deep as 70 or 80 meters at midday).
This movement up and down by the motile
phytoplankton is called a diurnal migration.
This daily movement is only in response to light
intensity. If the day is overcast and very
little light penetrates the sea, then the diurnal
movement will go start as soon or as deep.
The zooplankton that feed on the phytoplankton
also make this diurnal migration.
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Seasonal Distribution of Plankton
There are also seasonal differences in the
abundance of plankton.
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Seasonal Distribution of Plankton
The zooplankton populations follow the
phytoplankton.
The lag between the phytoplankton and zooplankton
numbers is due to

• Phytoplankton are single-celled and can double
  their population in twelve hours.

• The reproductive and growth cycles of the
  zooplankton are longer.

• The decline in phytoplankton after each bloom is
  the result of increased predation by the
  zooplankton population.

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The Distribution of Benthic Organisms
The distribution of the benthic organisms in the
sea is controlled mainly by the type of bottom or
substrate.
If the substrate is a hard bottom, like rock,
then the benthic populations are high and the
species varied.
Sand and mud bottoms support fewer numbers and
species of organisms.
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Groupings in Fish
Fish are well known for their clumping and
schooling behaviors.
When a group includes many different species of
fish it is called a clump.
When a group includes only a single species of
fish it is a school.
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Schooling Behavior in Fish
There are four main reasons for clumping or
schooling in marine fish.
1. Protection
2. Predation
3. Reproduction
4. Suitable Habitat
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Protection
Some fish travel in large schools to increase
their chance of survival from attacks by
predators.
Predators have a hard time focusing on a single
target, and often miss their prey altogether.
The sudden dispersal of the school may also
confuse the predator.
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Predation
Larger predators in the sea, like the tuna,
travel in large schools in order to capture prey
more efficiently.
A school of predators can encircle a school of
smaller fish and glean the stragglers from the
edges of the school without scattering the fish.
Many large predatory fish in the open sea will
travel in schools for better predation.
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Reproduction
Many species of fish school for reproductive
reasons.
Most species of bony fish reproduce by external
fertilization, in which the males release sperm
and the females release eggs into the water.
Schooling increases the rate of fertilization.
Snook, tarpon, and sheepshead are found in
schools only once a year just a few weeks prior
to mating.
Fish that already travel in schools will gather
into even larger schools for the mating season.
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Suitable Habitat
A final reason for marine fishes to be gathered
into one location is because of suitable habitat.
Often these groups are called clumps, because the
fish in the group will not be of the same
species.
Many benthic fish will be concentrated in much
greater numbers in an area like a reef or grass
flat community because that is the only suitable
habitat in the immediate area.
Within days after building an artificial reef in
the center of a large patch of poor habitat sand
bottom, fish of many different species will be
concentrated into a very small area of sea floor
around the new reef.