Mesopelagic zone

Question 1

Describe the mesopelagic zone

Answer 1

This is the twilight zone or dysphotic zone which extends 200-1000m deep. It accounts for 75% of the worlds oceans >200m deep.

Little light penetrates below 400m so there is no photosynthesis taking place.

Seasonal effects are dampened in this zone and waters are stable.

Question 2

What are some of the organisms found in the dysphotic zone and some of their adaptations?

Answer 2

Prawns, shrimp, amphipods, squid and fish.

Evolved with adaptations to exist in low light environment; large eyes, light generating organs - photophores (bioluminescence)

Question 3

What organism provides a link between the photic and dysphotic zones and why?

Answer 3

Many zooplankton rely on organic detritus falling from above for food.

Others, like euphausiids, practice diurnal vertical migration.

They swim up to the photic zone at night to feed. They swim down to the dysphotic zone during the day.

Can migrate to depths of 700m to 900m during the day

This provides food for predators lying at deeper depths.

Question 4

Describe general characteristics of mesopelagic fish

Answer 4

900 species live at 200m - 1000m

• enlarged eyes
• silvery scales and light organs.

Most species are small (<10cm)

• often completely transparent
• show diurnal migrations and feed on zooplankton

Predators larger (up to 2m)

• large teeth
• huge mouths
• distensible guts and body walls.

Question 5

Give some examples of mesopelagic species

Answer 5

The Atlantic Wolfish
-teeth designed to crush molluscs, shellfish and urchins. Found at 500m and can grow to 1.5m.

The Pacific Viperfish - can reach 4,400m - just 25cm long.
-large teeth and large pupil and eyes.