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1

What are the two zones within the pelagic zone?

Neritic zone = over continental shelf
Oceanic zone = beyond the shelf break

2

Features of pelagic zone

Heterogenous environment
Vertical and horizontal heterogeneity of light, temperature, oxygen, wind-driven currents, mixing of water masses
Leads to differences in spatial distributions of organisms

3

Dominant pelagic macrofauna

Large zooplankton (jellyfish)
Oceanic nekton

4

Adaptations of pelagic macrofauna

-Buoyancy: swim bladders of slow moving fish, seals have accessory air sacs, sharks and mackerel have lipids to aid buoyancy
-Locomotjon: body shapes to create propulsive force and streamlining to reduce resistance
-Adaptations for defence (e.g. shoaling)
-Camouflage (cryptic colours)
-Sensory systems (echolocation)
-Reproduction (spawning migrations)

5

Humpback whale migration

26 days average (4-90)
1.7km/hr mean speed
Whales from multiple feeding grounds congregate around the Antilles islands

6

Leatherback turtles

Spend most of their lives at sea but return to land to lay eggs -
“natal homing”
Feed on zooplankton (jellyfish)
Mature at 8-15 years, females mate every 2-3 years but breed annually

7

Results of tracking 8 Atlantic leatherbacks

-Extensive movement after egg-laying in Caribbean
-Very little consistency in movement
-Prevention of turtle by-catch from longlines needs to take place across Atlantic basin

8

Results of tracking 46 Eastern Pacific leatherbacks

More directional movement
Movement consistent - from Costa Rica, last Galapagos into South Pacific gyre
Migration corridor
Seasonally enforced Marine Protected Areas?

9

How do turtles navigate?

Potentially using geomagnetic cues
Luschi et al. 2007
Turtles displaced and satellite tracked
Those with magnets on their heads had longer homing paths than those without

10

Atlantic bluefin tuna migration

Thunnus thynnus - large marine predator
Basis for highly profitable fishery - caught using longlines and purse seines
Can live for 30 years, matures at 4-8 years
Downing grounds in Mediterranean and Gulf of Mexico
Western population breed in Gulf of Mexico, forage towards eastern-Atlantic
Eastern population breed in Mediterranean, forage towards western-Atlantic
Populations overlap but generally distinct
Rooker et al. 2008

11

Movement ecology - finding prey

Marine predators must make foraging movements without knowing distribution of prey
An optimal search strategy may be “Lévy flight”

12

Describe Lévy flight strategy

Many small movements when you have found a food source, but fewer larger movements when searching for areas with food
Ideally, the Lévy exponent is 2, basking sharks reached 2.3
Lévy-like movements observed in sharks, teleosts, sea turtles and penguins

13

What are most movements in the ocean?

Straight ballistic trajectories
Less of these movements in coastal waters