Download Dewey Notes 09 Life in the Ocean

EOS 110 Earth System I
EOS 110 Earth System I
Life in the Oceans
The basis of all life is the production of organic compounds
(e.g. proteins, lipids) from inorganic materials (e.g.
NO3− , PO43− , H 2O , CO2 ) plus light or chemical energy.
- Life is found in all parts of the ocean, top to bottom.
Photosynthesis
Plants need to convert raw materials around them into useable
energy and products. To do this they need an external energy
source à the sun.
Generally, plants create chemical energy in the form of
hydrocarbons (sugars) by combining CO2 and H2O.
- Of the 15 million known species, 17% are in the ocean.
- About 1% of the world’s biomass is in the ocean.
- However, 40-50% of photosynthesis occurs in the ocean.
Autotrophs: produce own food energy from
(photosynthesis) or chemical (chemosynthesis) energy.
light
Heterotrophs: food energy comes from consumption of other
organisms.
- Herbivores: eat autotrophs
- Carnivores: eat heterotrophs
- Omnivores: eat both autotrophs and heterotrophs
6CO2 + 6H2O + solar energy à C6H12O6 + 6O2
In this process, plants release oxygen. Respiration is the
reverse process (requiring enzymes to metabolize sugar).
However, plants need special chemicals and compounds (i.e.
chlorophyll) to help complete the chemical cycles, these
essential inorganic materials are called
Locomotion
Nutrients
Planktonic (floaters): horizontal motions are determined by the
prevailing ocean currents, while larger zooplankton are capable
of vertical migration.
Nektonic (swimmers): capable of sustained, directed motion,
independent of ocean currents.
Benthic: (bottom dwellers): live in or near the bottom.
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The most important nutrients are nitrogen and phosphorus, in
the oxidized forms of nitrate NO3 and phosphate P2O5.
Nitrogen is needed for protein structures, phosphorus for cells
and DNA replication. Silicon and Calcium are needed for body
tissue and shells, and trace metals and vitamins include: Fe, Cu,
Mg, Zn. Fortunately, seawater has almost everything a plant
could want.
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EOS 110 Earth System I
EOS 110 Earth System I
Plants and Animals
Limitations to Plant Growth
CO2 is dissolved from the atmosphere, where terrestrial life
forms over-produce it. Not usually a limiting factor.
H2O is plentiful in the ocean. So…
Oceanic life forms generally increase in size/biomass as they
increase in complexity, from simple single cell bacteria to large
mammals.
1) Light limited growth. Light can only penetrate several
hundred metres in crystal clear water. In turbid, silty, or
biologically active water, this can be reduced to tens of
metres. The depth over which light can penetrate with
sufficient energy for photosynthesis is the photic zone.
Also, light may be seasonally limited (i.e. in the Arctic).
Trophic
Level
Organism
Example
5 - 100 µm
1
Phytoplankton
2
Zooplankton Larvea Ciliates
100 - 500 µm
2) Nutrient limited growth. As plants grow, they use up the
available nutrients, and growth will slow or stop when one
or more of the necessary nutrients become depleted.
Nutrient transport depends on ocean currents and turbulent
mixing.
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Zooplankton
Euphausiid
2 -10 mm
4
Small Fish
Herring
2 – 20 cm
5
Large Fish
Tuna
50 – 200 cm
Re-Cycling Nutrients
Assuming a 10% energy transfer between trophic levels, then it
will take 10 kg of phytoplankton production for each gm of
tuna (large fish) production. Whales have figured out, that for
their massive needs, it is inefficient to pass the food through
intermediate trophic levels, so the largest beasts on Earth eat
some of the smallest (zooplankton).
As dead life forms and waste (detritus) settle through the water
column, they are re-eaten and re-cycled by other life forms.
Decomposition of this organic material by Bacteria play the
dominant role in re-cycling nutrients. However, decomposing
ammonia can take up to three separate bacteria before Nitrate is
returned to the ecosystem. Bacteria use chemosynthesis to
process food, where chemical reactions provide the energy,
without the need of sunlight.
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Dinoflagellates
Size
(µm=10-9m)
Global distribution of phytoplankton (primary) production.
http://seawifs.gsfc.nasa.gov/SEAWIFS/IMAGES/SEAWIFS_GALLERY.html
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EOS 110 Earth System I
EOS 110 Earth System I
Temperature
Predation: Zooplankton and Fish
We’ve discussed the role of temperature in determining the
density of seawater, causing the ocean to stratify, but
temperature has two additional impacts on biology.
Although zooplankton are among the “drifters”, they usually
have the capability of swimming vertically: either up or down.
They need to be mobile to feed, and to avoid being eaten.
1) Colder seawater is denser than warmer seawater.
2) Colder seawater has a higher viscosity than warm seawater.
3) Colder seawater slows biological processes (e.g. metabolic
rates) and diffusion across membranes (e.g. osmosis).
Plant and animal tissue is typically denser than seawater and
sinks. Because cold seawater is denser and “thicker”,
phytoplankton sink more slowly in colder water. Also, they
will sink more slowly if they have a larger surface area (like a
parachute). Small objects have more surface area per volume
than large objects, so plants will have a better chance of
“floating” near the surface (euphotic zone) if they are small. In
arctic regions, where the water is cold, plankton (phyto and
zoo) can grow larger because the water is denser and “thicker”
(higher viscosity).
For any one region, temperature variations in the ocean are
small (1-3°C) . This “stable” environment tends to limit the
diversity of species: 2% of all species are plankton (drifters)
and nekton (swimmers), 16.4% are benthic (bottom dwellers),
the remaining 83.3% of all species are terrestrial.
For a zooplankton, water seems very “thick” (viscous), perhaps
like us swimming in honey. Catching food is not easy, so they
use ciliary action, where by small antennae are “waved” to
generate a weak current towards their mouths. Swimming is
limited to vertical migrations through the water column to feed,
avoid prey, and to replicate.
Larger nekton (fish) can swim and control their position both
horizontally and vertically. They also use more advanced
sensory organs (eyes and pressure sensors) to find food, avoid
prey, and find a location for reproduction.
Examples:
Daily migration of zooplankton: eat food or be eaten
Salmon migration:
spawn and growth
Gray Whale migration:
Birth and food
Why do terrestrial environments cause so much more diversity?
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EOS 110 Earth System I
EOS 110 Earth System I
Benthic Ecosystems
Benthic Communities
Species that live either on or in the ocean sediments are
benthic. Bacteria and filter feeders that re-cycle nutrients are
perhaps the most important. They are either predators or rely
on chemosynthesis.
In coastal regions, photosynthetic plants can “anchor”
themselves and grow to macroscopic size. This in turn can
create a generous habitat for diverse and varied conditions that
will support more species à ecosystems.
Ecosystems
A portion of the environment defined by the local species and
habitat, and the way they interact, is called an ecosystem. The
species are all the life forms, from bacterial, to plant, to animal
that live within a region. The habitat is the physical and
chemical characteristics which determine the “health” of the
local region for supporting varied life forms.
Species within a habitat can interact in three basic ways:
1) Compete: demand similar needs from their habitat
2) Co-exist: are not in competition, but do not contribute
directly to the betterment of each other.
3) Symbiotic relation: depend directly on each other for food,
protection, etc.
Some may be permanent residents, while others may be
migratory on various time scales (daily to annual).
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- Sparse number of individuals, but many different species
due to varied geological environments
- Scavengers, predators, and bacteria à no photosynthesis
- Bacteria decompose “waste” by chemosynthesis
- Slow metabolic rates and limited oxygen slows respiration
C6H12O6 + 3O2 à 6H2O + 6CO2
Hot Vents
- Initial energy source is the dissolved minerals (chemical
energy) in the escaping seawater
- Bacteria use chemosynthesis to convert chemical energy
into biological (carbon based) tissue
- Rest of “local” ecosystem feeds on this food source, either
directly or indirectly.
Eco-Dynamics: Kelp Forests – Sea Urchins – Sea Otters
- Kelp forests provide food and shelter for an entire
ecosystem
- Sea Urchins eat kelp
- Sea Otters eat sea urchins
- Take away the otters, urchins eat all the kelp, forest dies.
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