Diel Vertical Migration

OCN 621

Karen E. Selph, OCN 621 Spring 2009

Outline

Definition

Who does it? How fast?

Migration cues

Why?

Variations: seasonal, ontogenic, reverse

Biogeochemical implications

Karen E. Selph, OCN 621 Spring 2009

Diel Vertical Migration: Definitions

Usually involves migration into food-filledshallow water at night, and descent into relativelyfood-depleted depths during the day. NormalDVM is when migration occurs at dawn and dusk.

2 general patterns: Nocturnal migration (as above): most common Reverse migration: surface rise during the day, night-

time descent to a maximum depth.

Karen E. Selph, OCN 621 Spring 2009

How widespread?

Freshwater and marine systems

Occurs in all major groups ofzooplankton

Extent/occurrence varies with life stageand/or sex, season, geographic location,and general weather conditions

Karen E. Selph, OCN 621 Spring 2009

Examples of Diel Vertical Migrators

These phyla have representatives that DVM, but not allspecies within these phyla migrate:

Crustacea: dominant group: copepods, especially the calanoids,and euphausiids (krill)

Siphonophores Chaetognaths Squid Fish Protists: Reverse DVM (down at dusk, up at dawn)

Ciliates (e.g., autotrophic Mesodinium rubrum) Dinoflagellates

Karen E. Selph, OCN 621 Spring 2009

Amplitude and extent of migration

Amplitude (depth range): 10s of cm to 100sof meters, and at all depths down to theabyssopelagic zone

Occurs ocean-wide, but especially in highlyproductive tropical areas.

Occurs over diel, seasonal and ontogenictime scales

Karen E. Selph, OCN 621 Spring 2009

How fast do they do it?

Speeds ranging from 3.24 m/h (0.9 mm/s) inthe small copepod Paracalanus parvus to215 m/h (60.2 mm/s) in the krillMeganyctiphanes norvegica (i.e., slower insmaller swimmers than larger ones).

Downward speeds are often faster thanupward speeds, probably due to gravity.

Karen E. Selph, OCN 621 Spring 2009

Deep Scattering Layers Moving deep scattering layers are due to diel vertical

migrators

Look like false sea bottoms on echograms

Formed by larger crustaceans, small fish with swimbladders, and occasionally copepods and heteropods

from Lalli & Parsons 1997

Day-time deepscattering layersin Saanich Inlet,BC, Canada

Karen E. Selph, OCN 621 Spring 2009

Example: ADCP, NE Atlantic

Wade & Heywood 2001

Main scattering layer: ascent at 3-4 cm/s, descent at 10 cm/s

increasing scattering

Karen E. Selph, OCN 621 Spring 2009

ADCP &MOCNESS

Courtesy of M. Zhou

Antarctica

Karen E. Selph, OCN 621 Spring 2009

MOCNESS

Karen E. Selph, OCN 621 Spring 2009

Euphausiasuperba

Karen E. Selph, OCN 621 Spring 2009

Vertical Migrators at BATS(Sargasso Sea, Atlantic Ocean)

Steinberg et al. 2000

Karen E. Selph, OCN 621 Spring 2009

Proximate Cue

Light the major cue: in particular theintensity of downwelling irradiance islinked to timing of migration and amplitude.

Is the absolute magnitude of light or the rateof change of light that zooplankton use ascues? Rate of change hypothesis morewidely supported by evidence and scientificcommunity.

Karen E. Selph, OCN 621 Spring 2009

Total Solar Eclipse, 30 June 1973

Solid Line: Vertical position of the 0.2 µW cm-2 nm-1 isolume

DSL: Vertical position of the sonic scattering layer during the eclipse.

The gap in the record was caused by ship repositioning for betterobservation.

From Kampa 1975 Deep-Sea Res 22:417-423.

isolu

me

DSL

SR

Karen E. Selph, OCN 621 Spring 2009

Light cues: Longer residence time at thesurface during winter months

Hays 2003

North Atlantic copepods:size also impacted length ofstay at the surface

Karen E. Selph, OCN 621 Spring 2009

Why do it? Most favor the hypothesis that DVM allows zooplankton to

avoid visual predation in the surface layers by takingtemporary refuge in the darker depths during the day

Cost vs. Benefit: reduced feeding period vs. reducingprobability of predation (“better hungry than dead”)

If this hypothesis true, then expect ascent at dusk and descent at dawn, and DVM will be more pronounced in more conspicuous individuals, and the amplitude of migrations will vary with the abundance and activity

of planktivorous fish

In fact, Reverse DVM also could be explained by this, as thepredators of those doing the R-DVM are themselves doingDVM (invertebrate predators).

Karen E. Selph, OCN 621 Spring 2009

Visibility & Relative Predation Risk

Vulnerability to visualpredation varies withlight intensity & preysize

It should also dependupon opticaltransparency of thewater (i.e., particleload).

DeRobertis 2002

Karen E. Selph, OCN 621 Spring 2009

Calanus pacificus:adult females

• Trawls for larval planktivorous fish• Stomach contents of larval fish examined for presence/absence of C. pacificus• Also looked at night/day distributions of C. pacificus (± 75 m)• Found that when significant numbers of fish, DVM behavior strong and vice versa

Bollens & Frost 1989

V = index ofvertical migrationF = fish abundance

Karen E. Selph, OCN 621 Spring 2009

Egg-bearing females more attractive to predators...

Photo by K.E. Fischer

When presented with egg & non-egg bearingfemales, Pacific herring ingested 4.67 timesas many ovigerous females.

Bollens & Frost 1991

Euchaeta elongata

Karen E. Selph, OCN 621 Spring 2009

Seasonal/Ontogenic Vertical MigrationLalli & Parsons 1997

Karen E. Selph, OCN 621 Spring 2009

Calanus pacificus

lipid storessufficient for winter

Karen E. Selph, OCN 621 Spring 2009

Some fish and sharks migrate,too...

Karen E. Selph, OCN 621 Spring 2009

Example of vertical migration to maintain position

Karen E. Selph, OCN 621 Spring 2009

Reverse Diel Vertical Migration

This is the oppositeof DVM: organismcome into surfacewaters during theday to feed, andsink to unlit depthsat night

Pseudocalanus sp. in Dabob Bay, WA

Ohman et al. 1983

Top: Vertical distributionof copepod during day (white)and night (black).

Bottom: Distributions of potential invertebrate predatorsof Pseudocalanus.

Karen E. Selph, OCN 621 Spring 2009

Seasonalvariation

Ohman 1990

P. newmani femalesPseudocalanus newmani

• 2 stations (shallow & deep)

• displaying diel vertical migration, reverse DVM and no migration

• migration or absence thereof correlated with predator presence

Karen E. Selph, OCN 621 Spring 2009

Salp migrations inthe Subarctic Pacific

Cyclosalpa bakeri

Top: Day and night distributions ofCyclosalpa bakeri at Stn. P in Aug. 1988

Bottom: Gut pigment contents as afunction of time of day.

Purcell & Madin 1991

Primary predators not visualMigration enables reproduction

Karen E. Selph, OCN 621 Spring 2009 Jarvis 2003

Karen E. Selph, OCN 621 Spring 2009

Contribution of Migrants to C & N flux

Al-Mutairi & Landry 2001note: these are minimum flux estimates, as they don’t include deathof migrants at depth, under-sampled micro-nekton, dissolved organic excretion or inter-zonal fecal transport.

Karen E. Selph, OCN 621 Spring 2009

Steinberg et al. 2000

Karen E. Selph, OCN 621 Spring 2009

Active area of research...

Deep-Sea Research I, 2009, 1777-1791

Concluded that DVM behavior resulted in 15% of theannual total POC flux at 150 m, mainly through

respiration at depth

One reference of many:

Karen E. Selph, OCN 621 Spring 2009

Kobari et al. 2003 -- Neocalanus, W. Subarctic Pacific

Karen E. Selph, OCN 621 Spring 2009

Biogeochemical Implications Active transport of material from euphotic zone to

deep (i.e. food in zp gut is metabolized at depth).

Numerous studies to date have drawn five mainconclusions(1) inter-zonal migrants can significantly enhance oceanic

export fluxes via their DVM behavior,

(2) the relative importance of the active flux is highlydependent on the biomass of the migrating community,

(3) the relative importance of the active versus the passiveflux increases with increasing depth,

(4) inter-zonal migrants may provide a steady source ofnutrients to deep-sea microbial communities, and

(5) we should be including the active flux caused by DVMwhen modeling the cycling of biogeochemically importantelements.