Lecture 16 - Megafauna

Question 1

What is the average depth of water at the shelf break?

Answer 1

150m

Question 2

What percentage of the sea surface is the oceanic zone?

Answer 2

92%

Question 3

What percentage of the Earth’s surface area is the oceanic zone?

Answer 3

65%

Question 4

Why is the oceanic zone referred to as a heterogeneous environment?

Answer 4

It varies in physiological and biological parameters over large and small geographic scales.

Question 5

What are megafauna?

Answer 5

Large animals (over 40 kg)

Question 6

Megafauna are what type of selected animal?

Answer 6

K-selected

• Large
• Long-lived
• Low fecundity
• Vulnerable to exploitation

Question 7

What are top down effects?

Answer 7

Predation and grazing by higher trophic levels on lower trophic levels ultimately controls ecosystem function.

Question 8

What are bottom-up effects?

Answer 8

The nutrients supply to the primary producers that ultimately controls how ecosystems function.

Question 9

Give an example of top down effects.

Answer 9

Shift in killer whale behaviour resulted in declining sea otter numbers, resulting in explosion in sea urchin numbers, which overgrazed the kelp.

Question 10

What is a trophic cascade?

Answer 10

When predators limit the density and/or behaviour of their prey and thereby enhance survival of the next lower trophic level.

Question 11

Other than size, what can we classify organisms according to?

Answer 11

• Taxonomic group
• Lifestyle (e.g. sessile vs pelagic)
• Trophic level
• Habitat
• Depth

Question 12

What area do the public tend to associated megafauna with?

Answer 12

The tropics, because warmer waters are more accessible.

Question 13

How many species of marine megafauna are observed?

Answer 13

78

Question 14

Give the six categories of marine megafauna.

Answer 14

• Pelagic seabirds
• Cetaceans
• Pinnipeds
• Sharks
• Marine turtles
• Large pelagic teleost fish

Question 15

How many species of megafauna are there that belong to the group

a) Pelagic seabirds?
b) Cetaceans?
c) Pinnipeds?
d) Sharks?
e) Marine turtles?
f) Teleost fish?

Answer 15

a) Seabirds = 43
b) Cetacenas = 20
c) Pinnipeds = 6
d) Sharks = 4
e) Marine turtles = 4
f) Teleosts = 1

Question 16

Give some UK megafauna.

Answer 16

• Herring gull
• Atlantic puffin
• Great shearwater
• Harbour seal
• Fin whale
• Arctic tern
• Great skua
• Northern gannet

Question 17

Give some adaptations for buoyancy in marine megafauna.

Answer 17

• Some marine mammals have accessory air sacs.
• Some marine mammals use air trapped in dense wool undercoats.
• Swim bladders lost in fast-moving fish as they prevent rapid depth change.
• Many marine fish (sharks) rich in lipids that help with buoyancy.

Question 18

Give some examples of adaptations for locomotion in marine megafauna.

Answer 18

• Body shapes that create propulsive force, e.g. turtle flippers
• Body shapes that reduce resistance of body during movement, e.g. teardrop-shaped tuna.

Question 19

Describe the lifecycles of leatherback turtles.

Answer 19

• Pelagic and forage on zooplankton
• Reach maturity 8-15 years of age, females mate every 2-3 years but can breed annually
• Extensive movement after egg-laying with little consistency.

Question 20

How do turtles navigate?

Answer 20

Using geomagnetic cues

Question 21

Describe the migrations of Atlantic bluefin tuna.

Answer 21

• Western population breed in Gulf of Mexica, forage towards eastern-Atlantic
• Eastern population breed in Mediterranean, forage towards western Atlantic.

Question 22

Where are there mixed populations of Atlantic bluefin tuna?

Answer 22

On the feeding grounds of the Mid-Atlantic bight.

Question 23

What is an optimal strategy when searching complex prey landscapes?

Answer 23

Levy flight

Question 24

What is Levy flight?

Answer 24

Many small movements, and fewer larger movements.

Question 25

What is the ideal Levy exponent?

Answer 25

2

Question 26

What groups of marine megafauna display Levy-like movements?

Answer 26

Sharks, teleosts, sea turtles, penguins.