Base of the food chain
Marine Productivity
and Nutrient Cycling
What is at the base of terrestrial food
chains?
Plants
Of Fighting Phytos
and Super Zoops
In the ocean, microscopic
phytoplankton are at the base of
many marine food webs
Diatoms
Thalassiosira
Dinoflagellates
Diatoms
Asterionella
Phytoplankton
Chaetoceros
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Dinoflagellates have a tough
Ceratium
organic wall. They are common in
estuaries and shelf waters; many
produce cysts which can rest dormant
within the sediments
Pfiesteria piscicida
autotrophic
~250 micrometers long
heterotrophic “fish killer”
toxic algal blooms
Peridinium
Diatoms have shells made
of opaline silica; their shells
accumulate beneath areas of
high productivity to form
deposits called siliceous ooze.
heterotrophic
~50 micrometers long
Autotrophs
Why are land plants and marine phytoplankton at
the base of food chains?
Coccolithophores have
shells made of calcium
carbonate; these shells
accumulate on areas of the
seafloor above the CCD
and form deposits called
calcareous ooze.
They are autotrophs. Autotrophs produce
organic molecules from inorganic substances.
Plants & phytoplankton are photosynthetic
autotrophs.
They utilize the energy of the sun to drive the
biochemical reactions of photosynthesis:
6CO2 + 6H2O + inorganic + solar → C6H12O6 + 6O2
nutrients
carbon
dioxide
water
energy
nitrates, phosphates,
trace elements, & vitamins
glucose
oxygen
(simple sugar)
The opposite of this reaction is respiration (what animals do exclusively)
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Heterotrophs
Primary Productivity
The production of organic matter by all
autotrophs is called primary production.
All animals are heterotrophs; animals are
dependent on the primary producers either
directly or indirectly.
stored chemical energy: carbohydrates,
proteins, and fats
herbivores (“grazers”) feed directly on autotrophs
carnivores (“predators”) feed on live herbivores or
primary production is measured in
gC/m2/day
other carnivores
grams of Carbon per square meter per day
scavengers feed on carrion
Most primary production in the ocean is by
photosynthesis by microscopic, unicellular
phytoplankton; lesser amounts by:
Animals acquire energy through respiration:
C6H12O6 + 6O2 → 6CO2 + 6H2O + organic
by-products
glucose
oxygen
(simple sugar)
carbon
dioxide
water
photosynthetic bacteria (=cyanobacteria)
chemosynthetic bacteria
multicellular algae (seaweeds)
vascular plants in coastal waters (grasses, mangrove trees)
Solar radiation
Productivity Basics
Primary productivity by photosynthesis
requires two essential ingredients:
Low Latitudes
Mid-Latitudes
High Latitudes
solar energy and inorganic nutrients
if both are not readily available, productivity will be limited
dependent on incident radiation, absorption, scattering
varies with turbidity (murkiness), latitude, season
euphotic zone is the upper part of the photic zone
that receives enough light intensity to support net
productivity (productivity > respiration).
bottom of zone is called the compensation depth
at bottom, light intensity = ~1% of surface intensity
(in meters)
photic zone is from the surface to the depth at
which photosynthesis is still possible
Water Depth
1. Solar energy (radiation)
huge "solar
footprint"
0
PHOTIC ZONE
100
(depth of light penetration
is schematic only)
EUPHOTIC ZONE
200
(sunlit surface waters
where net productivity occurs)
Angle of solar incidence varies
with latitude and season
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Productivity Basics (cont’d.)
Primary productivity by photosynthesis
requires two essential ingredients:
solar energy and inorganic nutrients
if both are not readily available, productivity will be limited
2. Nutrients
macronutrients – required in large doses
-
nitrates (NO3 )
3 phosphates (PO4 )
4 silicates (SiO4 )
Note: In ocean waters and in phytoplankton tissues, the
ratio of N:P is 16:1 – known as the “Redfield Ratio”
so N is the “limiting nutrient”
micronutrients – required in small doses
trace elements (e.g., Fe, Cu, Mn, Zn, others)
vitamins
the principal source of nutrients is from the weathering of soils and rocks
on land; dissolved nutrients are delivered to the ocean by river runoff
so, where would you predict the
highest primary productivity?
along continental margins,
especially in coastal waters
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