The EpipelagicLife Near the Surface

Epipelagic/Photic zone

• Surface to 200 m• Warmest and best light for

photosynthesis• Divided into coastal and oceanic

zones

Epipelagic

• Nearly all primary production takes place within the epipelagic system.

• Primary Production: the conversion of CO2 into organic matter by autotrophs (phytoplankton).

• Supplies food (fish and zooplankton) to marine organisms and humans.

Feeding• Lacks deposit feeders but

suspension feeders are plentiful.• There are also many large predators

such as fish, squid, and marine mammals.

Plankton

• Plants or animals that float and drift with the current.• Phytoplankton = plant plankton.

• Main primary producers in epipelagic– Cyanobacteria, Diatoms, Dinoflagellates &

Coccolithophores.– Eaten by herbivores.

• Zooplankton = animal plankton.– A fundamental part of the epipelagic food web is the flow of

energy from phytoplankton to herbivorous zooplankton.– May be herbivores or carnivores.

Zooplankton• Copepods– Most abundant members of

the net zooplankton; practically everywhere in the ocean

– Most are omnivores• Krill– Dominant zooplankton in polar

seas– Omnivores that will eat

detritus (dead organic matter) including fecal pellets.

Meroplankton• Holoplankton– Spend their whole lives as plankton– Diatoms & Dinoflagellates

• Meroplankton– Temporary plankton– Invertebrate & Fish larvae

Nekton

• Large strong swimmers including fishes, marine mammals and squid.• Planktivorous nekton include:• Small fishes like herring, sardines and anchovies• The world’s largest fishes: the whale and basking

sharks.• Baleen Whales, seals, penguins.

Plankton Adaptations for the Epipelagic

• Must have an adaptation to keep from sinking -- must stay in epipelagic!

• Shells and skeletons are denser than water.• Organisms must increase their water

resistance so they sink slower OR make themselves more buoyant so they don’t sink in the first place.

Plankton Adaptations for the Epipelagic

• The higher the surface area, the higher the resistance and the slower the organism sinks. – Small organisms sink slower than large ones– Flat body shape– Long projections or spines increase surface area

• Increased buoyancy = doesn’t sink– Storing lipids such as oils or fats in the body

(diatoms, sharks & whales)– Pockets of gas (bubbles or vacuoles), or floats

Epipelagic Food Webs• Tend to be long and complex because they

contain many species and many epipelagic animals feed at different tropic levels.

• Basic flow of Energy: phytoplankton to zooplankton to small nekton to large nekton to top predators.

• Energy from one tropic level to the next:– Epipelagic herbivores convert more than 20%– Epipelagic carnivores convert more than 10%

Primary Productivity• The base of all

epipelagic food webs.• Some epipelagic

ecosystems are among the most productive on earth, while others are the “deserts” of the ocean.

• Phytoplankton need light and essential nutrients to perform photosynthesis.

So how do the nutrients get circulated?

• Overturn and mixing caused by the cooling of surface waters.

• Upwelling: the upward movement of nutrient-rich deep water towards the surface.

• The Coriolis Effect: the deflection of a water particle to the right in the N. Hemisphere and the left in the S. Hemisphere. Each layer of water moves slightly below the next creating an Ekman Spiral.

Ekman Spiral

Coastal Upwelling

• Carries huge amounts of nutrients into the photic zone.

• Major coastal upwelling areas are among the most productive waters of the epipelagic.

• Upwelling tends to be seasonal.

El Niño• Change in the surface

currents along the coasts of Chile and Peru.

• Every year, usually in December, the trade winds slack off, upwelling decreases and the water gets warmer.

• BUT, every few years, the surface water gets much warmer, and upwelling stops.

El Niño

• Trade winds stop• Warm currents push cold coastal currents back• California & Humboldt (Peru) currents are most affected

Local Effects

• No upwelling = no nutrients• Fish must move, adapt or die to find food• Fisherman have no fish to catch = no money

Global Effects

• Weather extremes including flooding, drought, hurricanes & blizzards