## Lab 7.1 – How does the abundance of phytoplankton vary over the course of a year?

Fundamental concept: Describe seasonal pattern in chlorophyll concentration over a year
Estimated time to complete
: 45 minutes
Data skills preparation: Lab 2.1 – Time series
Materials needed: None

Phytoplankton are the most abundant marine primary producers. They are found at the base of the marine food web, directly and indirectly supporting most of the life found in the oceans, including large animals such as whales. Because phytoplankton are photosynthetic, they contain the green pigment chlorophyll. The concentration of chlorophyll in the water can easily be measured using sensors and serves as a proxy for the abundance of phytoplankton: higher chlorophyll concentration indicates higher phytoplankton abundance, which in turn indicates higher primary production and more food availability for the rest of the food web.

In this activity, you will explore how chlorophyll concentration (and thus phytoplankton abundance and primary production) varies over the course of a year in the temperate Atlantic Ocean.

You can interact with the data by

• adjusting the date range shown by using the slider bar

### Orientation Quick Check Questions:

Answer the following quick-check questions to ensure that you are correctly reading the graph.

### Interpretation questions:

1. Describe the trends and patterns you see in the concentration of chlorophyll over the course of the year. Pay particular attention to the following: During which months does chlorophyll tend to be higher? Intermediate? Lower? During which months does chlorophyll tend to increase? Decrease?
2. Order the seasons from highest to lowest expected phytoplankton abundance. Assume the following seasons:
• Winter = December, January, February
• Spring = March, April, May
• Summer = June, July, August
• Fall = September, October, November
1. Based on what you know about photosynthetic primary production, which factors might affect chlorophyll concentrations? Formulate some preliminary ideas here that you will be able to explore in more detail in the next activity.

### Reflection question:

1. Right whales feed on copepods (zooplankton), which in turn feed on phytoplankton. Would the abundance of zooplankton in this area be expected to vary seasonally as well? Would the abundance be highest and lowest in the same months as phytoplankton? Why or why not?