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Plankton
Marine life is classified into three groups:
Plankton, Nekton, and Benthos
Plankton
Nekton
Benthos
Plankton
• Plankton refers to the drifting organisms
within the pelagic zone
• Phytoplankton are autotrophic,
photosynthetic algae, which form the base of
the marine food web
• Zooplankton are heterotrophic; the primary
(and in some cases secondary and tertiary)
consumers of the marine food web
Plankton form the base of the marine
food web
‘Bottom’ of the Food Chain
How are plankton classified?
• By Metabolism (autotrophic vs. heterotrophic)
• By Life History (meroplankton vs. holoplankton)
• By Taxonomy (Crustaceous vs. Gelatinous
zooplankton, for example)
http://www.whoi.edu/annualreport02/highlights/globec_en3.html
Phytoplankton
• Phytoplankton are responsible for 40% of all
the world’s photosynthetic food on Earth (and
95% of all the ocean’s!)
• Provide ~one half of all the oxygen we
breathe!
• Collectively, the production of organic
compounds from CO2 is referred to as primary
productivity
Phytoplankton
• Phytoplankton require nutrients, especially
nitrogen and phosphorus (macronutrients)
but also iron (micronutrients)
• For this reason, phytoplankton appear in
abundance (“blooms”) in regions of upwelling,
where cold, nutrient-rich water reaches the
photic zone
Global Primary Productivity
http://www.nasa.gov/centers/goddard/images/content/95573main_plankton_satellite.jpg
Localized Primary Productivity
• In tropical regions, there is plenty of sunlight
but productivity is limited by nutrients
trapped beneath the thermocline
• In polar regions, there are plenty of nutrients,
but sunlight (and sinking out of the photic
zone via mixing) limits productivity
• In temperate regions, the combination of
sunlight and nutrients is just right, but only
seasonally!
Tropical Productivity Profile
Primary Productivity in Temperate Regions
• Localized primary productivity occurs
seasonally, accompanied by physical changes
to the water column
• In temperate regions, primary productivity is
limited by light (winter) and by nutrients
(summer)
• Peak productivity occurs during spring, in an
abundance of phytoplankton known as a
“spring bloom”
Primary Productivity in Temperate Regions
• During winter, nutrients are at their highest,
but light is at its lowest
• In spring, solar energy reaching the photic
zone increases and nutrients are still abundant
• In summer, strong warming of the water
creates a seasonal thermocline which restricts
nutrients from reaching the photic zone
• In fall, storms enhance mixing, and a second
seasonal bloom results
Compensation Depth
• Net primary productivity is the amount of
carbon dioxide removed via photosynthesis
minus the amount of carbon dioxide released
by respiration
• Compensation depth refers to the depth in
the water column at which the rate of
photosynthesis equals the rate of respiration
– Above this depth, phytoplankton survive
– Below this depth, phytoplankton die
Phytoplankton
• Phytoplankton are mostly single-celled algae
(Kingdom Protista)
• There are 8 major types of phytoplankton, 2 of
which are most prominent:
– Diatoms
– Dinoflagellates
Diatoms
• Dominant (>5,600 species)
• Composed of silica shells
• Important source of nutrition for zooplankton
√
Dinoflagellates
• Can be autotrophic or heterotrophic!
• Most are planktonic, but others form symbiotic
relationships with coral (zooxanthellae) and
giant clams
• Flagella for movement
• Responsible for red tides
(harmful algal blooms)
Red Tide caused by Dinoflagellate
Harmful Algae Blooms (HAB’s)
Caused by dinoflagellates and other small flagellates
Zooplankton
• Zooplankton are the most numerous primary
consumers in the ocean
• The most important source of protein in the
oceans!
• Zooplankton eat bacteria, phytoplankton, and
other zooplankton!
• Nearly every major animal group is
represented in the zooplankton
Zooplankton
• Zooplankton are classified as either:
– Holoplankton
– Meroplankton
• Holoplankton are always plankton – they live
and die in the water column
• Meroplankton are only plankton for part of their
lives; many marine organisms begin their lives as
small planktonic organisms, but gain the ability to
swim or metamorphose into a benthic organism
Holoplankton
Once a copepod, always a
copepod…
Meroplankton
• Includes larval (very young) fish, crabs, clams,
squid, lobsters, starfish, etc.
Types of Zooplankton: Copepods
• Copepods are the most
abundant of all the
zooplankton (70%)
• Holoplanktonic
• Crustaceous
• Herbivorous,
Omnivorous,
Carnivorous, and
Parasitic
• Marine and freshwater
Copepods
• 14,000 species globally
• You, too, can become a copepodologist!
• Important source of protein for secondary
consumers!
Types of Zooplankton: Pteropods
Composed of calcium carbonate, CaCO3
Jellyfish and ctenophores are gelatinous
zooplankton!
Avoiding Predation
• Translucence and Transparency
• Outward spines for protection
http://www.microscopy-uk.org.uk/mag/artjun98/wimren2.html
• Swimming behavior and migration
The Greatest Migration on Earth
Increasing
Depth
Every night at dusk, swarms of
zooplankton migrate to the
surface, and return to depth
again at dawn
Deep-Scattering Layer
How to capture zooplankton
Quantitative
Zooplankton
Tows
Think Like Plankton
• Life in a pelagic habitat (no solid substrate); 3-D
• Properties of water
Properties of Water
• Water is viscous, ESPECIALLY if you are a very
small organisms living in it
• Reynolds number:
Re = inertial forces
viscous forces
Reynold’s Number
• For very small organisms, inertia is nonexistent
• Viscous forces dominate (low Reynolds
number) for small organisms, such as plankton!
• Inertial forces dominate (high Reynolds
number) for larger organisms, such as humans,
large fish or whales
Reynolds Number
http://brodylab.eng.uci.edu/~jpbrody/reynolds/figure3.gif