Marine life is classified into three groups: Plankton, Nekton, and Benthos

Plankton

NektonPlankton 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

http://www.nasa.gov/centers/goddard/images/content/95573main_plankton_satellite.jpg

Global Primary Productivity

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

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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

• Swimming behavior and migration

http://www.microscopy-uk.org.uk/mag/artjun98/wimren2.html

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 forcesviscous forces

Reynold’s Number

• For very small organisms, inertia is non-existent

• 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