Overview

During this interactive experience, students will explore how the actions of an agricultural farmer and an oyster aquaculture farmer impact the health of eelgrass in Malpeque Bay, and therefore the survival of other species in the habitat.

Background

Habitats can be very sensitive — even a small change such as a change of temperature or the availability of nutrients can alter the habitat. These changes can occur naturally, but humans also cause changes to occur.

Coastal runoff is a major source of nutrients in the ocean. When nutrients (nitrogen and phosphorus) are used as fertilizers on agricultural farms, water runoff can cause nutrient pollution in the water. Eutrophication occurs when an excess of nutrients leads to excessive plant and algal growth.

Ulva (sea lettuce) is a green seaweed that uses photosynthesis to make food. When there are lots of nutrients in the water, ulva grow and grow, both on the bottom and floating in the water. Too much growth in the water column creates so much shade that other Ulva and other species cannot get enough sunlight. Once the ulva start to die because of shading, bacteria and other organisms begin to decompose the dead organic matter. Their activity uses up a lot of the oxygen, creating areas of hypoxia (very low oxygen) on the seafloor. The areas of low oxygen make the habitat unsuitable for fish that live near the sea bottom: they either find another habitat or they die.

Eelgrass is a seagrass that is an important habitat-forming species. Its thick, long, green blades of grass make excellent habitat for small juvenile fish to hide in. Eelgrass also photosynthesizes, so when the ulva grows too thick, the eelgrass also cannot get enough sunlight. As the eelgrass dies, the fish lose their habitat.

Oyster aquaculture also affects the eelgrass in the Bay. The oysters are cultivated on floating platforms. Platforms cause a significant amount of shading on the coastal seafloor, limiting the amount of sunlight available for the eelgrass.

Related links

• NOAA — What is nutrient pollution?

• BBC — Eutrophication

Learning outcomes

Students use the scientific method to explore how changes in 1 variable (nutrients) impact another habitat variable (O₂) and the number of species in a habitat.

Note: The students can visually monitor the impact of the number of oyster platforms on the health of the bay, but the data collection sheet does not include that information.

Competencies

Critical thinker, Collaborator, Communicator

Focus question

What are the relationships between marine species and their habitats?

Learning objectives

• Make and record observations.

• Explore and interpret data using graphs.

• Explain how the agricultural farm and the aquaculture farm in Malpeque Bay impact the number of species in the habitat.

Before you get started

The data collection sheet is automatically generated, and cannot be altered. If you would like to provide different instructions, you will need to share those with your class.

Steps

The students’ activity guide for Bay watch prompts them to:

1. Reflect on their experience

2. Record their observations on land, on the surface of the water, and underwater

3. Graph the data that was recorded in the Bay watch data collection sheet.

4. Interpret the graph data and try to explain the relationships present in the data

5. (Optional) Create a social media post sharing what they’ve learned

Discussion points

• What factors are essential for a healthy marine habitat? Ask students to give specific examples based on your observations and data analysis.

• The agricultural farmer and oyster farmer need to make a living by producing crops, cows and oysters - but the impacts are not always positive. Suggest some ways to balance the needs of the habitat and its species with the needs of the farmers.