Week 7 Flashcards
What are the key bottom-up and top-down controls on phytoplankton growth?
Bottom-up (growth): Light availability, nutrients, temperature, and COβ.
Top-down (loss): Grazing, sinking, and viral infections.
What is the general equation for phytoplankton dynamics?
ππ/ππ‘ = π(π β π β π)
Where:
ππ/ππ‘: Rate of change in phytoplankton biomass.
π: Growth rate (function of light and nutrients).
π: Grazing rate.
π: Mortality (e.g., sinking, viral lysis).
What are key ecosystem models for phytoplankton dynamics?
Simple models: Focus on basic growth/loss terms (light, nutrients, grazing).
Complex models: Include multiple nutrient types and interactions between different phytoplankton and zooplankton groups.
How does Critical Depth Theory explain the spring bloom?
A bloom occurs when the mixed layer depth (Zmix) is shallower than the Critical Depth (Dcr), allowing sufficient light for positive net primary production.
What are the key features of the seasonal cycle at high latitudes?
Winter: Low light, high nutrients, deep mixing.
Spring: Bloom triggered by shallow Zmix.
Summer: Stratified, low-nutrient conditions.
Autumn: Secondary bloom possible as nutrients mix upward.
How does the seasonal cycle in shelf seas differ?
Stratification divides mixed, high-nutrient waters and stratified, high-light waters.
Seasonal blooms occur at fronts where nutrient mixing is sustained.
What is the role of turbulence and nutrient availability in shaping phytoplankton traits?
High turbulence, high nutrients: Diatoms dominate (large cells, fast growth).
Low turbulence, low nutrients: Small, efficient competitors (e.g., Prochlorococcus).
High nutrients, low turbulence: Red tide dinoflagellates (motile, toxic).
What are the features of low latitude oligotrophic systems?
Weak seasonality.
Permanently stratified, low-nutrient surface layers.
Production dominated by small cells (e.g., Prochlorococcus) using regenerated nitrogen.
How does Prochlorococcus adapt to low nutrient environments?
Some ecotypes have lost genes for nitrate/nitrite assimilation, relying on ammonium.
Specialized adaptations to varying degrees of oligotrophy through gene loss.
What is the f-ratio in stratified low-nutrient systems?
Consistently low, as production is dominated by regenerated nitrogen.
Where is the Deep Chlorophyll Maximum (DCM) typically found?
At the base of the mixed layer and the top of the nutricline in stratified oligotrophic systems.
What factors contribute to DCM formation?
High nutrients from below the nutricline.
Low light from surface attenuation.
Phytoplankton adapt to subsurface conditions.
How does phytoplankton community structure differ at the DCM?
Subsurface communities include diatoms and flagellates adapted to low light and higher nutrient conditions.
What are the characteristics of shelf sea fronts?
Mixed side: High nutrients, low light.
Stratified side: High light, low nutrients.
Enhanced phytoplankton biomass at the interface.
How are blooms sustained at shelf sea fronts?
Nutrient supply is maintained by tidal mixing at the front.
Name a phytoplankton species that blooms at shelf sea fronts.
Gyrodinium aureolum (Karenia mikimotoi), which is motile and often toxic.
What are mesoscale eddies, and how do they affect phytoplankton?
Rotating water masses that enhance primary production by upwelling nutrients (cyclonic eddies) or suppress it by downwelling (anticyclonic eddies).
How do cyclonic eddies enhance productivity?
Upwelling shoals the thermocline and nutricline, bringing nutrients into the euphotic zone.
What phytoplankton are typically found in mesoscale eddies?
Diatoms often dominate due to the availability of new nitrate in the euphotic zone.
How does the spring bloom differ between high and low latitude systems?
High latitude: Pronounced spring bloom due to strong seasonality in light and stratification.
Low latitude: Weak or absent bloom due to permanent stratification and low nutrients.
Compare phytoplankton dynamics at Bermuda (BATS) and Hawaii (HOT).
BATS: Seasonal winter bloom from deep mixing penetrating the nitracline.
HOT: No strong bloom; permanently stratified, dominated by Prochlorococcus.
What is Margalefβs Mandala, and how does it relate to phytoplankton?
A conceptual model linking turbulence and nutrient availability to phytoplankton size and traits.
How do light and nutrient gradients shape phytoplankton distributions?
Surface: High light, low nutrients.
Subsurface: High nutrients, low light.
Growth occurs where light and nutrients overlap (e.g., at the DCM).
How do satellite observations aid in understanding phytoplankton distributions?
They provide large-scale data on chlorophyll-a, DCM locations, and mesoscale eddy dynamics.
