Patterns of Zooplankton Diel Vertical
Migration in the Global Ocean
Devika Balachandran
K. Allison Smith
August 12, 2011
What is DVM?
Depth (m)
• Diel vertical migration is best defined as the vertical
displacement of an individual or group of individuals,
which occurs with diel periodicity (Huntley 1985)
Tim
e
Why is DVM important?
• Major component of the biological pump
Biological pump
Questions to address
• What percent of zooplankton biomass leaves
the euphotic zone during the day?
• To what depths do migrating species move
during the day?
NOAA Database
- Filter data manually and
using R and Excel
- Use ephemeris to flag
data points as day or night
(based on sun’s elevation)
- Organize data with R and
graph with Excel
- Make maps plotting sites
(longitude, latitude) using
Generic Mapping Tools
(GMT)
Sites used: Day and Night Values Close Together
What % of zooplankton biomass leaves the
euphotic zone during the day?
• Results presented as ratio of Day/Night values
– A ratio r <1 suggests that zooplankton are migrating out of the euphotic
zone during the day, while an r > 1 suggests that zooplankton are migrating
into the euphotic zone during the day
– If r < 1, % biomass leaving euphotic zone during the day = (1 r) 100
• Ex: if r = 0.4779, it appears as though 52.21% of the zooplankton
biomass is leaving the euphotic zone during the day

1
– If r > 1, % biomass entering euphotic zone during the day = (1  r ) 100
• Ex: if r = 1.7438, it appears as though 42.65% of the zooplankton
biomass is entering the euphotic zone during the day

What % of zooplankton biomass leaves the euphotic zone during the day?
- When considering values less than
1, results are comparable to values
that have been presented in the
literature
- 15-50% of all metazoan
zooplankton biomass above 500 m
perform migrations (Longhurst and
Harrison, 1988)
- When all values are considered,
results are not comparable to
values presented in the literature
- Most of the data was presented
in counts (num/m3), which is not
the most accurate unit for
zooplankton biomass
Emerging patterns?
Spatial distribution of values less than and greater
than/equal to 1
<1
≥1
A ratio r <1 suggests that zooplankton are migrating out of the euphotic zone
during the day, while an r ≥ 1 suggests that zooplankton are migrating into the
euphotic zone during the day
Summary
• DVM is a component of export fluxes and should not be
overlooked in nutrient flux calculations
• Studies that are specifically researching DVM show clearer
DVM results than analysis of data from cruises not
researching DVM
– Perhaps due to methods (studies researching DVM more often report
biomass in density or volume, while other cruises more often report
biomass in counts, which does not represent biomass as accurately)
• It is not yet clear what global patterns of DVM are, but DVM
appears to occur globally, so perhaps with more data,
patterns may emerge
Future Studies
• More cruise data from the Atlantic
• Acquire more data from a variety of databases
• Analysis of acoustic data combined with tow
data in order to find patterns