Life in the Ocean

1
Life in the Ocean
Lecture 17
OEAS-306
April 2, 2009

• Outline
• Zones of the Ocean
• Light Availability
• Photosynthesis and Chemosynthesis
• Primary Production
• Nutrient Cycles
• Osmosis/Diffusion/Active Transport

2
Zones of the Ocean
All of these zones experience different values of

• Light
• Temperature
• Nutrient Availability
• Salinity
• Pressure
• Gas Solubility

3
Classification of Marine Environments and Marine
Organisms
Benthic vs. Pelagic
Benthic Meaning bottom, encompasses the
seafloor and includes such areas as shores,
intertidal zones, coral reefs, and the deep
seabed.
Pelagic Meaning open sea, encompasses water
column from the surface to the greatest depths of
the ocean.
Oceanic vs. Neritic
Oceanic Generally any part of the ocean seaward
from the continental shelf break (gt 200 m).
Neritic also called the sublittoral zone, is
the part of the ocean extending from the low tide
mark to the edge of the continental shelf.
Plankton vs. Nekton
Plankton organisms that are incapable of making
their way against a current. Passive drifters.
Can be phytoplankton (plants) or zooplankton
(animals)
Nekton free swimming organisms that can move
independently from the oceans currents.
4
Light Availability Differs Significantly in
Different Zones of the Ocean.
In the open ocean, light is only available over a
very small percentage of the water column ( less
than 15).
5
Light Provides the Dominant Source of Energy to
Drive Biological Production in the Oceans.
Photosynthesis
photosynthesis
respiration
6
Photosynthesis is limited to a relatively small
portion of the overall ocean.
In the open ocean, light is only available for
photosynthesis over a very small percentage of
the water column ( about 1 ).
7
Chemosynthesis
Conversion of one or more carbon molecules and
nutrients into organic matter using the oxidation
of inorganic molecules (like Hydrogen Sulfide)
8
Relatively recently, scientists discovered very
rich communities living around hydrothermal vent
systems.
No sunlight, so organisms derive energy from
chemosynthesis.
Sulfur oxidizing bacteria serve as the base of
the food web.
9
Synthesis of organic materials from inorganic
substances by photosynthesis (or chemosynthesis)
is called primary productivity
Measured in units of grams of carbon bound into
organic material per square meter of ocean
surface area per year (gC/m2/yr).
10
Comparison of primary productivity in marine
communities.
11
Regions of high primary production inferred from
satellite
12
1) Primary production in the ocean is comparable
to that on land. 2) However, marine biomass (mass
of living tissue) is significantly smaller than
the terrestrial biomass. 3) This is demonstrates
the efficiency of cycling in marine ecosystems.
Nutrient cycle from producer to consumer and back
much more rapidly in marine ecosystems that
terrestrial.
Biomass and Primary Productivity are NOT the same.
13
Trophic Pyramid
Despite efficiency of marine ecosystems, energy
is still used at each step in the pyramid. As
a result it takes 10,000 kg of phytoplankton to
produce 1 kg of tuna.
14
Food Webs Disperse Energy through Communities

• Diatoms, and other primary producers, convert the
  energy from the sun into food used by the rest of
  the oceanic community.
• (left) A simplified food web, illustrating the
  major trophic relationships leading to an adult
  killer whale.
• The arrows show the direction of energy flow the
  numbers on each area represent the trophic level
  at which the organism is feeding.

15
Zones of the Ocean Experience Very Different
Temperatures

• Temperature influences metabolic ratethe rate at
  which energy-releasing reactions proceed within
  an organism
• Metabolic rate approximately doubles with a 10C
  temperature rise.
• Cold blooded (ectothermic) organisms have an
  internal temperature that matches the
  environment.
• Warm blooded (endothermic) organisms maintain a
  relatively constant internal temperature.

16
Temperature Also Controls Gas Solubility
As temperature rises, metabolic rates go up but
gas solubility goes down. This can cause
problems for organisms that live where there are
large changes in temperature.
17
These are the building blocks of all living
organisms (comprise over 99)
A nutrient is a compound required for the
production of organic matter.
Micronutrients are needed, but only in very small
quantities.
18
In many parts of the ocean, external inputs of
nutrients are very small
This requires that nutrients are internal recycled
19
The Carbon Cycle
Carbon dioxide dissolved in seawater is the
source of the carbon atoms assembled into food
(initially glucose) by photosynthesizers and most
chemosynthetic organisms. When this food is
metabolized, the carbon dioxide is returned to
the environment. Some carbon dioxide is converted
into bicarbonate ions and incorporated into the
shells of marine organisms. When these organisms
die, their shells can sink to the bottom and be
compressed to form limestone. Tectonic forces may
eventually bring the limestone to the surface,
where erosion will return the carbon to the ocean.
20
The Nitrogen Cycle
Most organisms cannot use Nitrogen gas (N2), but
require other forms including Nitrate (NO3-),
Nitrite (NO2-) or Ammonium (NH3)
Therefore, Nitrogen must be fixed or bound to
oxygen or hydrogen through chemical reactions
performed by specialized bacteria.
21
The Phosphorus Cycle
The phosphorus cycle. Phosphorus is an essential
part of the energy-transporting compounds used by
all of Earths life-forms. Much of the
phosphorus-containing materials in the ocean
falls to the seabed, is covered with sediment, is
subducted by tectonic forces, and millions of
years later returns to the surface through
volcanic eruptions.
22
Osmosis
Osmosis is the diffusion of water through a
membrane

• An isotonic solution contains the same
  concentration of dissolved solids (green) and
  water molecules (blue) as a cell. Cells placed in
  isotonic solutions do not change size since there
  is no net movement of water.
• A hypertonic solution contains a higher
  concentration of dissolved solids than a cell
  does. A cell placed in a hypotonic solution will
  shrink as water moves out of the cell to the
  surrounding solution by osmosis.
• A hypotonic solution contains a lower dissolved
  solids concentration than a cell does. A cell
  placed in a hypotonic solution will swell and
  rupture as water moves by osmosis from the
  environment into the cell.

23
Transport into cells can occur through 3
mechanisms
Diffusion
Osmosis
Active Transport
24
Summary

• The environments populated by marine life may be
  classified by their physical characteristics.
• Each environment can experience significantly
  different environmental conditions due to light
  availability, temperature, nutrient availability,
  salinity and pressure.
• Light for photosynthesis is only available near
  the surface, where energy from the sun is
  converted into organic mater.
• Photosynthesis provides nearly all the energy
  that drives marine ecosystems.
• Productivity is expressed in grams of carbon
  bound into carbohydrates (food) per square meter
  of ocean surface per year (gC/m2/yr).
• Marine ecosystems are very efficient at cycling
  nutrients from producers to consumers and back.
  This leads to high productivity but low biomass.
• To maintain this efficiency, nutrients most be
  constantly recycled
• Diffusion, osmosis, and active transport, are all
  important processes in moving substances within
  and between living cells.