Download Chapter 10 Biological Productivity in the Ocean

Chapter 10
Biological
Productivity
in the Ocean
©2003 Jones and Bartlett Publishers
Food Webs and
10-1 Trophic Dynamics
An ecosystem is the totality of the
environment encompassing all chemical,
physical, geological and biological parts.
• Ecosystems function by the exchange of matter and
energy.
• Material is constantly recycled in the ecosystem, but
energy gradually dissipates as heat and is lost.
– Energy flows downhill, materials cycle!
• All ecosystems are composed of:
– Autotrophs (producers)
– Heterotrophs (consumers)
10-1 Autotrophs
• Autotrophs use an abiotic source of energy to convert inorganic
material into organic compounds for growth and reproduction.
• Autotrophs produce food, and are known as “primary producers”.
• Inorganic vs. organic material.
– Inorganic = CO2, NH3, NO32-, PO43-, etc
– Organic = living, or derived from living tissue (proteins, lipids,
carbohydrates, nucleic acids, or containing C-C bonds (petroleum
products).
• Plants are autotrophs and the primary producers in most
ecosystems.
– Energy source is the Sun.
• Chemosynthetic bacteria are autotrophs and primary producers
in deep vent communities
– Energy source is inorganic sulfur molecules, NOT SUN!
Examples of Marine Autotrophs
phytoplankton
Seaweeds
Eel grass
Mangroves
Salt marsh
Chemosynthetic
bacteria
Food Webs and
10-1 Trophic Dynamics
• All other organisms are heterotrophs, the
consumers and decomposers in
ecosystems.
• Heterotrophs derive their energy from
organic matter (animals, plants, detritus,
dissolved organic matter)
• Herbivores eat plants and carnivores eat
animals.
Examples of Marine Heterotrophs
fish
crab
krill
whale
copepod
Heterotrophic
bacteria
Tube worms
dinoflagellate
Food Webs and
10-1 Trophic Dynamics
The word “trophic” refers to nutrition.
• Trophic dynamics is the study of the
nutritional interconnections among
organisms within an ecosystem.
• Trophic level is the position of an organism
within the trophic structure of an
ecosystem.
– Autotrophs form the first trophic level.
– Herbivores are the second trophic level.
– Carnivores occupy the third and higher trophic
levels.
– Decomposers form the terminal level.
Food Webs and
10-1 Trophic Dynamics
• A food chain is the
succession of
organisms within an
ecosystem based upon
trophic dynamics. (Who
is eaten by whom.)
Food Webs and
10-1 Trophic Dynamics
• A food web consists of interconnected
and interdependent food chains- more
realistic.
Food Web
Food Webs and
10-1 Trophic Dynamics
• An energy pyramid is the graphic representation of
a food chain in terms of the energy contained at
each trophic level.
• The size of each level in an energy pyramid is
controlled by the size of the level immediately
below.
Energy
Energy Pyramid
Ecosystem Model: Definition
• A tentative, explanatory, generalization
about how ecosystem functions (i.e., a
hypothesis).
• Structure of model arises from
observations.
• Tentativeness requires that models be
verified by experimentation or further
observations.
Ecosystem Model: Generic
Ecosystem Model
• Ecosystem models show:
– Trophic pathways (carbon flows)
– Ecological efficiency
– Resilience to species loss
– Biological magnification
– Biogeochemical pathways (flows of other
elements, Ca, Si, N, P, etc.).
Phytoplankton blooms and
10-1 cell division
Increased cell
division
causes bloom
Food Webs and
10-1 Trophic Dynamics
As the primary producers, plants require
sunlight, nutrients, water and carbon
dioxide for photosynthesis.
• Photosynthesis occurs within organelles called
chloroplasts, or within lamellae of prokaryotes.
• The formula for photosynthesis is:
Sunlight + 6 CO2 + 6 H2O  C6H12O6 (sugar) + 6 O2.
Food Webs and
10-1 Trophic Dynamics
lamellae
Diatom: Eukaryote
Blue-green algae: Prokaryote
10-1 Photosynthesis
10-1 Respiration
Animals must consume pre-existing
organic material to survive.
• Animals break down the organic
compounds into their inorganic
components to obtain the stored energy.
• The chemical formula for respiration is:
C6H12O6 (sugar) + 6 O2  6 CO2 + 6 H2O + Energy.
Food Webs and
10-1 Trophic Dynamics
Photosynthesis
Sunlight + 6 CO2 + 6 H2O  C6H12O6 (sugar) + 6 O2.
Respiration
C6H12O6 (sugar) + 6 O2  6 CO2 + 6 H2O + Energy.
*Respiration is similar to the combustion of gasoline in your
automobile. It produces energy, carbon dioxide and water.
Food Webs and
10-1 Trophic Dynamics
• The energy recovered during respiration is
used for movement, reproduction and
growth.
– Respiration occurs in organelles called
mitochondria
– Animals and plants respire
Food Webs and
10-1 Trophic Dynamics
• The food consumed by most organisms is
proportional to their body size.
• Smaller animals eat smaller food and larger animals
eat larger food, although exceptions occur.
Food Webs and
10-1 Trophic Dynamics
Heterotrophic dinoflagellates feeding on
photosynthetic dinoflagellate
Food Webs and
10-1 Trophic Dynamics
Blue whale (~30 m)
Krill (~0.01 m)
Food Webs and
10-1 Trophic Dynamics
• The basic feeding styles of animals are:
– Grazing
– Predation
– Scavenging
– filter feeding
– deposit feeding
feed on plants
actively pursue and capture food
feed on dead stuff (detritus)
filter plankton or detritus from water
filter food from sediment
Food Webs and
10-1 Trophic Dynamics
Cow grazing on grass
Dinoflagellate grazing
on another
dinoflagellate
…or any zooplankton on phytoplankton, sea urchin on algae, snail
on seaweed, etc.
Food Webs and
10-1 Trophic Dynamics
Filter-feeder
predator
scavenger
Food Webs and
10-1 Trophic Dynamics
Deposit feeder
(polychaete worm)
Food Webs and
10-1 Trophic Dynamics
•Population size is dependent upon food supply
and grazing pressure.
Food Webs and
10-1 Trophic Dynamics
Bacteria are the decomposers; they
break down organic material and release
nutrients for recycling.
Nutrient Cycling
Food Webs and
10-1 Trophic Dynamics
• Few bacteria are capable of completely
degrading organic material into its
inorganic components. Most operate in
succession with other bacteria to
decompose material in a series of stages.
• Bacteria also serve as food for other
organisms either directly or indirectly.
Food Webs and
10-1 Trophic Dynamics
• Bacteria can be divided into those that are
aerobic or anaerobic.
– Aerobic: (“with air”)- uses oxygen in air.
– Anaerobic: (“without air”), in sediments. Use
oxygen contained within molecules, such as
sulfate
SO42-
2O2 + S2-
Hydrogen sulfide, H2S, then forms. “Rotten
egg” smell
Food Webs and
10-1 Trophic Dynamics
• Bacteria can also be divided into those that are
autotrophic or heterotrophic.
– Autotrophic: obtains food by photosynthesis
• Blue-green algae (Prochlorococcus sp. – most abundant
organism on Earth?).
– …or chemosynthesis - from inorganic compounds.
• Volcanic vent bacteria
– Heterotrophic: obtains food by eating other
organic matter.
• E. coli, etc.
Photosynthetic vs. Chemosynthetic Food Chain
Volcanic vent communities at Hydrothermal
vent sites
Black smoker at hydrothermal vent
Volcanic vent communities at Hydrothermal
vent sites
Volcanic vent communities at Hydrothermal
vent sites
Chemosynthetic
bacteria live
inside worms
and produce
organic matter
Red Riftia tube worms thrive near a sea vent.
Are volcanic vent communities at
Hydrothermal vents good analogs for life on
other planets?
Below the icy
surface of Galileo’s
moon Europa, heat
from tectonic forces
may allow liquid
water to exist.
Do chemosynthetic
bacteria exist here
as well?
Food Chains and Energy Transfer
Food chains transfer energy from
one trophic level to another.
• Biomass is the quantity of living matter per
unit area or per volume of water.
• With each higher trophic level, the size of
organisms generally increases, but their
reproductive rate, number and the total
biomass decrease.
Food Chains and Energy Transfer
Large body size,
low biomass,
slow growth.
Small body size,
high biomass,
fast growth.
Food Chains and Energy Transfer
• The two major food chains in the ocean are
the grazing food chain and the Detritus
food chain (non-living wastes form the
base of the food chain).
Grazing Food Chain
Phytoplankton
Zooplankton
Detritus
Deposit Feeder
Detrital Food Chain
Nekton
Nekton
•Only about 10-20% of energy is transferred between
trophic levels and this produces a rapid decline in
biomass at each successive trophic level.
Food Chains and Energy Transfer
•Only about 10-20% of
energy is transferred
between trophic levels and
this produces a rapid decline
in biomass at each successive
trophic level.
•Energy lost as kinetic
motion and maintenance
respiration.
•Energy lost building nonnutritional tissue (bones,
chitin exoskeleton,
diatom frustules, etc.)
0.1
1
10
100
Energy
Food Chains and Energy Transfer
Food Chains and Energy Transfer
0.1
108 g algae
0.1
107 g krill
106 g small fish
0.1
0.1
104 g small human
105 g large fish
Why not make trophic chain shorter?
104 g small human
0.1
105 g algae
0.1
0.1
105 g krill
105 g small fish
General Marine Productivity
Primary production is the total amount
of carbon (C) in grams converted into
organic material per square meter of sea
surface per year (gm C/m2/yr).
• Factors that limit plant growth and reduce
primary production include solar radiation
and nutrients as major factors and
upwelling, turbulence, grazing intensity
and turbidity as secondary factors.
• Only 0.1 to 0.2% of the solar radiation is
employed for photosynthesis and its
energy stored in organic compounds.
10-2 General Marine Productivity
• Macronutrients and micronutrients are
chemicals needed for survival, growth and
reproduction in large and small quantities,
respectively.
• Upwelling and turbulence return nutrients
to the surface.
• Overgrazing of autotrophs depletes the
population and leads to a decline in
productivity.
• Turbidity reduces the depth of light
penetration and restricts productivity even
if nutrients are abundant.
Wave and Tide Turbulence
10-2 General Marine Productivity
Productivity varies greatly in different
parts of the ocean in response to the
availability of nutrients and sunlight.
• In the tropics and subtropics sunlight is
abundant, but it generates a strong
thermocline that restricts upwelling of
nutrients and results in lower productivity.
• High productivity locally occurs in areas of coastal
upwelling, in the tropical waters between the
gyres, and in coral reefs.
10-2 General Marine Productivity
• In temperate regions productivity is
distinctly seasonal.
• Polar waters are nutrient-rich all year but
productivity is only high in the summer
when light is abundant.
Variations in Primary Productivity
10-3 Global Patterns of Productivity
Primary productivity varies from 25 to
1250 gm C/m2/yr in the marine
environment and is highest in estuaries
and lowest in the open ocean.
• In the open ocean primary productivity
distribution resembles a “bull’s eye“
pattern with lowest productivity in the
center and highest at the edge of the
basin.
• Water in the center of the ocean is a clear
blue because it is an area of downwelling,
above a strong thermocline and is almost
devoid of biological activity.
10-3 Global Patterns of Productivity
• Continental shelves display moderate
productivity between 50 and 200 gm
C/m2/yr because nutrients wash in from
the land, and tide- and wave- generated
turbulence recycle nutrients from the
bottom water.
• Polar areas have high productivity because
there is no pycnocline to inhibit mixing.
• Equatorial waters have high productivity
because of upwelling.
• Centers of circulation gyres, which occupy
most of the open ocean, are biological
deserts.
The Sargasso Sea and Vertical Profiles
10-3 Global Patterns of Productivity
It is possible to estimate plant and fish
productivity in the ocean.
• The size of the plankton biomass is a good indicator
of the biomass of the remainder of the food web.
• Annual primary production (APP) is equal to
primary production rate (PPR) times the area for
which the rate is applicable.
APP = PPR x Area (to which applicable )
• Transfer efficiency (TE) is a measure of the amount
of carbon that is passed between trophic levels and
is used for growth.
• Transfer efficiency varies from 10 to 20% in most
food chains.
10-3 Global Patterns of Productivity
• Potential production (PP) at any trophic
level is equal to the annual primary
production (APP) times the transfer
efficiency (TE) for each step in the food
chain to the trophic level of the organism
under consideration.
PP = APP x TE (for each step)
• Although rate of productivity is very low
for the open ocean compared to areas of
upwelling, the open ocean has the greatest
biomass productivity because of its
enormous size.
10-3 Global Patterns of Productivity
• In the open ocean the food chains are
longer and energy transfer is low, so fish
populations are small.
• Most fish production is equally divided
between areas of upwelling and coastal
waters.
• Calculations suggest that the annual fish
production is about 240 million tons/yr.
10-3 Global Patterns of Productivity
• Overfishing is removing fish from the ocean faster
than they are replaced by reproduction and this will
eventually lead to the collapse of the fish
population if not regulated.
Haddock Catch in North Sea
Biological Productivity of
10-4 Upwelling Water
Upwelling of deep, nutrient-rich water
supports large populations of
phytoplankton and fish.
• The waters off the coast of Peru normally is an area
of upwelling, supporting one of the world’s largest
fisheries.
• Every three to seven years warm surface waters in
the Pacific displace the cold, nutrient-rich water on
Peru’s shelf in a phenomenon called El Nino.
• El Nino results in a major change in fauna on the
shelf and a great reduction in fishes.
• This can lead to mass starvation of organisms
dependent upon the fish as their major food
source.
The Ocean Sciences:
Volcanic Vent Communities
• Volcanic vent communities have been
discovered along sea-floor spreading
ridges.
• The base of the food webs in these vent
communities consists of
chemosynthesizing bacteria, which obtain
energy to manufacture food by oxidizing
hydrogen sulfide gas.
• Seawater heated by magma leaches metal
from the basalts and these get precipitated
as sulfide and sulfate minerals that form
chimneys on the sea floor.
Plumbing in a Black Smoker
The Ocean Sciences:
What Causes El Niño?
• When the trade winds are strong, cold,
nutrient-rich water upwells offshore Peru,
supporting high primary productivity and
large populations of anchovy.
• When air-pressure patterns change, the
trade winds weaken and even reverse
direction, dragging warm, nutrient-poor
water to Peru and initiating an El Niño
event.
10-1 Photosynthesis
10-1 Photosynthesis
10-1 Photosynthesis