Biological Productivity
Conditions for Life in the Sea
Consider the main biochemical reaction for
life in the sea, and on earth in general:
6H2O + 6CO2 + energy + nutrients = C6H12O6 + 6O2
Focus on left side of equation
What is in short supply in the sea and thus
limits the amount of life in the ocean??
Absorbing Nutrients
6H2O + 6CO2 + energy + nutrients = C6H12O6 + 6O2
 Phytoplankton
are
base of the food chain
 Most important
primary producers of
complex sugars and
oxygen
Lauderia sp.
ARCOD@ims.uaf.edu
Open Ocean Food Webs
Coccolithophores
Copepods
Barrie Kovish
Pacific Salmon
Vicki Fabry
Pteropods
Present Ocean Food Web – Complex
Ocean
ecosystem
Food Web
interactions based on a low CO2 ocean
Provided by James Barry MBARI
Primary Producers
Seafloor community
Microbial
Remineralization
Absorbing Nutrients
 Nutrients
absorbed by
plants through
diffusion across a
semi-permeable
membrane
Lauderia sp.
Diffusion:
molecules move from high to low concentrations
Which Nutrients are in Short
Supply?
 Nitrogen
(N) as Nitrate NO3 (-2)
 Phosphorus (P) as Phosphate PO4 (-2)
 Silicon (Si) as Silicate SiO4 (-2)
Phosphate and Nitrate in the Pacific
Silicate in the Pacific
Biolimiting Nutrients
 N,
P, and Si are exhausted first in Eq.
surface waters during photosynthesis
 Essential to the growth of phytoplankton
 If these biolimiting nutrients increase in
sea water, life increases
 If these biolimiting nutrients decrease in
sea water, life decreases
 Where would you expect to find the highest
biomass in the Pacific??
CZCS Global Primary Production
How Does Nutrient Distribution Compare w/
Dissolved Oxygen?
6H2O + 6CO2 + energy + nutrients = C6H12O6 + 6O2
 O2
is high in the
surface and mixed
layer
 O2 decreases to a
minimum at base of
thermocline
 O2 then steadily
increases with depth
Dissolved O2 Reverse of
Nutrients
Why is the Concentration of
Oxygen High in the Mixed Layer??
Hint #1: How and where is oxygen produced
in the sea???
6H2O + 6CO2 + energy + nutrients = C6H12O6 + 6O2
Hint #2: How can oxygen be mixed
downward from the atmosphere into the
ocean?
How is Oxygen Removed from the
Thermocline & Slightly Below??
Dead and decaying organic matter sinks
downward from surface waters



Rate of sinking decreases
as it encounters the cold,
dense water of the
thermocline
Material decays (oxidizes)
at the thermocline, which
strips O2 out of the water
and returns nutrients to
the sea
Cold, nutrient-rich water
of the thermocline is
returned to sunlit surface
waters by way of
upwelling
CZCS Global Primary Production
Marine Ecology
Basic Ecology
 physical
and chemical parameters
affecting distribution and abundance
 An ecosystem includes both the living
(biotic) and non-living (abiotic) portions
of the environment.
– Examples include: salt marshes, estuaries,
coral reefs, the North Pacific Gyre.
Classification of Organisms
by Environment
 horizontal:
neritic | oceanic
 vertical:
– epipelagic (top) / euphotic (good)
– mesopelagic (middle) / disphotic (low)
– bathypelagic (deep) / aphotic (without)
– abyssopelagic (“bottomless”)
Divisions of the Marine Environment
Figure 9-1
Classification of Organisms
by Lifestyle
 Scientists
have established another
classification scheme to categorize biota
on the basis of lifestyle. The major groups
are:
– plankton (floaters)
– nekton (swimmers)
– benthos (bottom dwellers)
Plankton
 weak
swimmers, drifters, unable to
counteract currents.
– Phytoplankton (plants)
– Zooplankton (animals)
Nekton
 active
swimmers capable of counteracting
currents.
– Fish
– Squids
– Reptiles
– Birds
– Mammals
Distribution of
Marine Lifestyles
 16.7%
of Earth’s animals are marine
 2% inhabit pelagic environment (most of
the oceans are cold and dark)
 98% are benthic!
Benthos
Epiflora
or epifauna live on the sea
bottom.
Infauna live in the sea bottom.
 Benthic
plants - restricted to shallow
waters (light)
 Benthic animals occur everywhere from
shallow depths to the deep sea.
Research Video Clips:
“Live fast, die young...”
Hydrostatic Pressure
 Pressure
caused by the height of water.
 Function of water height and water density
 Pressure generally increases at a rate of 1
atm per 10 m of water.
( or 16 psi per 10 m depth)
Think You’re Under
Pressure Now?
Hydrostatic Pressure
(Cont.)
 enormous
in the deep sea yet animals live
there.
 Animals do not contain gases.
 However, mesopelagic fish which have
gas-filled swim bladders to help maintain
neutral buoyancy
– unable to move rapidly between depths
– pressure change could cause bladder explode.