Lecture 9 - Vertical Migration

Question 1

Types of Vertical Migrations

Answer 1

Seasonal
Ontogenetic
Diurnal

Question 2

Diurnal vertical migrations

Answer 2

about 2 h
symmetrical about dawn and dusk
speeds of 2-400 m/h

Question 3

Vertical migrations result in changes in

Answer 3

predator spps
prey spps
abundance of predators/prey
O2 and pH
light, temp, speed/direction of water

Question 4

Characteristics of shallow migrating fish

Answer 4

shiny sides

ventral photophores

Question 5

Characteristics of migrating crustaceans

Answer 5

well pigmented eyes

ventral photophores

Question 6

Anthropocentric view of vertical migration

Answer 6

“mesopelagic migrators”

deep living spps come up each night

Question 7

Alternate view of vertical migration

Answer 7

(Childress’s preferred view)
Epipelagic migrators - shallow spps which migrate down each day
Nocturnal spps seeking refuge during the day

Question 8

How does latitude correlate with depth of migration?

Answer 8

Different latitudes have different water temps which change the depth of migration for similar spps

Question 9

Two primary aspects of vertical migration

Answer 9

Cues
Driving (selecting) factors

Question 10

What evidence is there for _____ being the primary cue for vertical migration?

Answer 10

_light_
VM parallels changes in light
Depth variations at night depend on moon's brightness
Animals come up during a solar eclipse
Artificial lights drive animals down

Question 11

Vertical migrators are ______ specialists who have what?

Answer 11

nocturnal
Large eyes - be vulnerable to visual overload in daylight
Dark bodies - wrong color for day

Question 12

Hypotheses for vertical migration

Answer 12

1. Food at surface
2. Predators at surface
3. Low O2 at depth
4. Metabolic advantage
5. Hardy (?)

Question 13

What evidence is there for the Food at surface hypothesis?

Answer 13

Plankton feeders come up at night to feed on plankton

Larger fish follow their prey up at night

Question 14

What evidence is there for the predators at surface hypothesis?

Answer 14

Predators are more effective during the day so prey move down during the day

Question 15

What evidence is there for the Low O2 hypothesis?

Answer 15

Come up to feed at night
Go down during the day to digest in lower O2 environment when fish requires less energy (float and digest)
Complete migrations have been shown for well developed low O2 layers

Question 16

What evidence is there for the Metabolic hypothesis?

Answer 16

Come up to feed at night
Go down to digest in lower temp
More energy for growth and repro
(does not explain isothermal water columns)
(energy cost of movement might cancel out benefit)

Question 17

What does the Hardy hypothesis say?

Answer 17

Move down to control horizontal movement by decreasing the influence of turbulence during the day
(not testable)

Question 18

Horizontal distributions

Compared to terrestrial or shallow, faunal boundaries are…

Answer 18

can be very wide/broader
related to more subtle environmental changes
migration (active and passive) more important

Question 19

Upwelling

Answer 19

Bringing up nutrients to the surface waters

Question 20

Factors influencing distributions

Answer 20

Temp structure of water column
Salinity
PO4
Zooplankton biomass (primary productivity)
Depth v. temp
Distance from shore
Nutrient availability

Question 21

Productivity

Answer 21

Levels of available nutrients which are defined by terrestrial sources (runoff) and upwelling

Question 22

Polar regions

Answer 22

highly productive (isothermal, terrestrial input, upwelling)

Question 23

Subpolar regions

Answer 23

relatively productive (cool temps near surface)

Question 24

Subtropical Gyres

Answer 24

Low productivity (warm temp at considerable depth, stable away from land)

Question 25

Tropical regions

Answer 25

Productive (cool temp closer to surface)

Question 26

O2 minima in tropics

Answer 26

Highly productive (eastern margins of ocean basins, upwelling, reduce diversity, cool temps near surface, closer to shore)