Lecture 9 - Vertical Migration Flashcards
Types of Vertical Migrations
Seasonal
Ontogenetic
Diurnal
Diurnal vertical migrations
about 2 h
symmetrical about dawn and dusk
speeds of 2-400 m/h
Vertical migrations result in changes in
predator spps prey spps abundance of predators/prey O2 and pH light, temp, speed/direction of water
Characteristics of shallow migrating fish
shiny sides
ventral photophores
Characteristics of migrating crustaceans
well pigmented eyes
ventral photophores
Anthropocentric view of vertical migration
“mesopelagic migrators”
deep living spps come up each night
Alternate view of vertical migration
(Childress’s preferred view)
Epipelagic migrators - shallow spps which migrate down each day
Nocturnal spps seeking refuge during the day
How does latitude correlate with depth of migration?
Different latitudes have different water temps which change the depth of migration for similar spps
Two primary aspects of vertical migration
Cues Driving (selecting) factors
What evidence is there for _____ being the primary cue for vertical migration?
_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
Vertical migrators are ______ specialists who have what?
nocturnal
Large eyes - be vulnerable to visual overload in daylight
Dark bodies - wrong color for day
Hypotheses for vertical migration
- Food at surface
- Predators at surface
- Low O2 at depth
- Metabolic advantage
- Hardy (?)
What evidence is there for the Food at surface hypothesis?
Plankton feeders come up at night to feed on plankton
Larger fish follow their prey up at night
What evidence is there for the predators at surface hypothesis?
Predators are more effective during the day so prey move down during the day
What evidence is there for the Low O2 hypothesis?
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
What evidence is there for the Metabolic hypothesis?
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)
What does the Hardy hypothesis say?
Move down to control horizontal movement by decreasing the influence of turbulence during the day
(not testable)
Horizontal distributions
Compared to terrestrial or shallow, faunal boundaries are…
can be very wide/broader
related to more subtle environmental changes
migration (active and passive) more important
Upwelling
Bringing up nutrients to the surface waters
Factors influencing distributions
Temp structure of water column Salinity PO4 Zooplankton biomass (primary productivity) Depth v. temp Distance from shore Nutrient availability
Productivity
Levels of available nutrients which are defined by terrestrial sources (runoff) and upwelling
Polar regions
highly productive (isothermal, terrestrial input, upwelling)
Subpolar regions
relatively productive (cool temps near surface)
Subtropical Gyres
Low productivity (warm temp at considerable depth, stable away from land)
Tropical regions
Productive (cool temp closer to surface)
O2 minima in tropics
Highly productive (eastern margins of ocean basins, upwelling, reduce diversity, cool temps near surface, closer to shore)
