3.4 Phytoplankton

Summary

Phytoplankton are the primary producers in aquatic ecosystems, influencing water turbidity and nutrient cycling. Their growth is driven by key factors including nutrient availability, light, and temperature. Phytoplankton concentration can be measured by indicators like chlorophyll a, which is commonly used. Mechanisms such as sedimentation, resuspension, and grazing by zooplankton regulate their populations. Some species, like cyanobacteria, can control buoyancy, allowing them to thrive under calm conditions. In deeper lakes, thermal stratification impacts nutrient mixing and phytoplankton growth. The interplay of these factors shapes the aquatic ecosystem and phytoplankton dynamics.

Takeaways

• 😀 Phytoplankton is the primary producer in aquatic ecosystems, influencing water turbidity.
• 😀 Phytoplankton concentration can be measured by cell count, chlorophyll a levels, or dry weight per liter.
• 😀 Chlorophyll a concentration is commonly used to estimate phytoplankton levels due to ease of measurement.
• 😀 Nutrients, light, and temperature are the primary factors affecting phytoplankton growth.
• 😀 The composition of phytoplankton communities depends on species and environmental conditions.
• 😀 Dry weight of phytoplankton contains 2% chlorophyll a, 0.5% phosphorus, and 3% nitrogen.
• 😀 Nutrient concentration in water limits the growth of algae and phytoplankton.
• 😀 Other mechanisms suppressing phytoplankton concentrations include sedimentation, resuspension, light limitation, and zooplankton grazing.
• 😀 Phytoplankton in standing water will settle due to their inability to swim or control buoyancy.
• 😀 In deep lakes, thermal stratification can reduce phytoplankton growth by limiting nutrient circulation.
• 😀 Some phytoplankton species, like cyanobacteria, can regulate buoyancy and swim, leading to the formation of harmful surface layers under calm conditions.

Q & A

What is the main primary producer in an aquatic ecosystem?

Phytoplankton is the main primary producer in an aquatic ecosystem.

What factors influence the concentration of phytoplankton in the water?

Factors that influence phytoplankton concentration include nutrients, light, temperature, and environmental conditions.

How is the concentration of phytoplankton commonly measured?

The concentration of phytoplankton is commonly measured using chlorophyll a concentration, as it is relatively easy to measure.

What nutrients are essential for phytoplankton growth?

Nutrients essential for phytoplankton growth include phosphorus, nitrogen, and other trace elements.

What is the general composition of dry weight in phytoplankton?

The general composition of dry weight in phytoplankton consists of 2% chlorophyll a, 0.5% phosphorus, and 3% nitrogen.

What are some mechanisms that suppress phytoplankton concentrations in the water?

Mechanisms that suppress phytoplankton concentrations include sedimentation, resuspension, flushing, light limitation, and grazing by zooplankton.

How does sedimentation affect phytoplankton populations in shallow lakes?

In shallow lakes with limited water depth, phytoplankton sedimentation results in a high reduction of the population.

What role do aquatic plants play in phytoplankton resuspension?

In lakes with high aquatic plant density, resuspension is limited, which leads to clearer water between the plants.

What is thermal stratification, and how does it affect phytoplankton growth?

Thermal stratification occurs in deep lakes during summer when the water layers separate, preventing circulation and reducing nutrient concentration in the top layer, which limits phytoplankton growth.

How do some phytoplankton species regulate their buoyancy?

Certain phytoplankton species, especially cyanobacteria, can regulate their buoyancy using flagella, allowing them to swim or adjust their position in the water column.

What happens when harmful phytoplankton species, like cyanobacteria, regulate their buoyancy?

When cyanobacteria and other harmful species regulate their buoyancy, they can form fluorescent green layers on the water surface, especially under calm weather conditions.