Vertical Distribution and Migration of Zooplankton

Stephen M. BollensSchool of Biological Sciences, and

School of Earth and Environmental SciencesWashington State University Vancouver

Variability !!!!

Unpredictability?

Euchaeta elongata

(Bollens & Frost 1991)

(Longhurst 1976)

(Wiebe et al. 1992)

(Wiebe et al. 1992)

(Lough & Potter 1992)

Calanus sinicus

(Uye et al. 1990)

Euchaeta elongata

Adult female

(Bollens & Frost 1991)

Calanus pacificus

Adult female

(Bollens & Frost 1989)

Variability !!!!

Unpredictability?

ACKNOWLEDGEMENTS

Coastal Ocean Processes (CoOP) Program of NSF,Wind Events and Shelf Transport (WEST) Project

• Overall goal: to critically examine the role that wind-driven transport plays in shelf productivity.

• More specific research question: Does wind-driven transport of water directly affect the distribution of zooplankton on the shelf, or are zooplankton behaviorally adapted to avoid such transport via diel vertical migration?

Pseudocalanus newmani Adult femalesJune 20-21, 2000

-0.40 -0.20 0.00 0.20 0.40

10-0

20-10

30-20

40-30

50-40

60-50

70-60

80-70

Dep

th (

m)

Proportion of population

Mean Day

Mean Night

0.40 0.20

Metridia pacifica-lucens Adult femalesJune 20-21, 2000

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

10-0

20-10

30-20

40-30

50-40

60-50

70-60

80-70

Dep

th (

m)

Proportion of population

Mean Day

Mean Night

1.0 0.8 0.6 0.4 0.2

Copepod Diel Vertical MigrationBehavior on the Middle Shelf

Dep

th (

m)

Jun 20 Jun 21 Jun 22 Jun 23 Jun 24

0.00 0.00 0.00 0.0012.00 12.00 12.00

SUMMARY OF VERTICAL MIGRATION STUDIES

• More generally, it is a strategy to maximize the gains of energy intake (feeding) while minimizing the probability of death (predation)

• Future studies of the consequences of this behavior need to explicitly link the detailed (species-specific) biological observations with circulation/hydrodynamic models

• In habitats that have vertically sheared, differently-directed flow fields, such as estuaries and coastal upwelling systems, position maintenance is another plausible ultimate cause of vertical migration behavior

• Predator avoidance is widely held to be the most likely ultimate cause or adaptive significance of diel vertical migration in zooplankton

• Pertinent to both upwelling and relaxation (downwelling) periods