Patterns of Zooplankton Diel Vertical Migration in the Global Ocean

Devika BalachandranK. Allison SmithAugust 12, 2011

What is DVM?• Diel vertical migration is best defined as the vertical

displacement of an individual or group of individuals, which occurs with diel periodicity (Huntley 1985)

Time

Dep

th (m

)

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 = • Ex: if r = 0.4779, it appears as though 52.21% of the zooplankton

biomass is leaving the euphotic zone during the day

– If r > 1, % biomass entering euphotic zone during the day = • Ex: if r = 1.7438, it appears as though 42.65% of the zooplankton

biomass is entering the euphotic zone during the day€

(1−1

r) ×100

€

(1− r) ×100

- 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)

What % of zooplankton biomass leaves the euphotic zone during the day?

- 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 ≥ 1A 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