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
Learning outcomes
Explore how changes in one variable (nutrients) impact another habitat variable (O2) and the number of species in a habitat.
Competencies
Critical thinker, Collaborator, Communicator
Focus question
What are the relationships between marine species and their habitats?
Learning objectives
Make and record observations.
Explain how the agricultural farm and the aquaculture farm in Malpeque Bay impact the number of species in the habitat.
Use the power of observation to determine the ultimate balance between nutrients, oysters and species.
Time
15 - 25 min
Before you start the workshop
Set up the computer/projector to display Bay Watch.
Load the video Ulva Overload in one tab. Test your sound.
In a second tab, load Bay Watch . Test to make sure it is working.
Workshop
Introduction
10 min
Welcome!
Explain to the group they are going to learn how farming can impact marine habitats, and that they will be challenged to help farmers balance their needs with keeping the marine ecosystem healthy.
Ask learners:
What do you know about how farms affect water systems?
What do you know about how farms affect marine habitats?
Ulva overload
Explain that they will start by watching a short video to learn a bit more about how farms can impact the Bay.
Play video
Use the introduction slider of Bay Watch and/or information below to review the essential information in the video.
Habitats can be very sensitive
When nutrients (nitrogen and phosphorus) are used as fertilizers on agricultural farms, water runoff can cause nutrient pollution in the water. This can lead to excessive plant and algal growth.
For example, we just learned how too much nutrients can cause ulva (sea lettuce) to grow so much that ulva and other species cannot get enough sunlight and they decay of these plants uses up a lot of the oxygen. 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.
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.
Investigation
10 min
Welcome to the Bay
Explain the activity using the following as a guide:
What to say: “Here is our Bay. We are going to try and figure out what the ultimate balance between nutrients, oysters and species is. I will be the farmer controlling how much nutrients goes on my farm and how many oyster platforms I have.”
Action: Slide the nutrients up and down and change the number of oysters in the bay.
What to say: “You will be the scientist underwater. Your job is to observe what is happening to the species, habitat and oxygen level and communicate your observations when I ask you.”
Action: Set nutrients back to 0. Go to goggles in top right corner to change view to underwater.
Round 1: Observe
Set nutrients and oysters to lowest level and have group describe the bay: What does the water look like? Is the farm doing well?
Toggle to the underwater view
Ask 1-2 learners to share their observations.
Round 2: Note the changes
Increase nutrients to max level.
Ask the group to describe the agricultural farm and bay - What does the water look like now? Is the farm doing better? How do we know? Or Why?/Why not?
Toggle to the underwater view. Encourage participants to look around and make observations.
Next, toggle back to the farm and decrease the nutrients.
Return to the underwater view and ask learners to describe the changes that occurred. Invite participants to share their observations -What did the water look like when nutrients was highest? What species were present? What happened when it was decreased?
Change the focus to the oyster beds. Increase the number of oyster beds to 10. Ask participants to make observations. What happened when there were more oyster beds?
Round 3: Challenge
Ask the group: What do you think is the ultimate balance between nutrients, oysters and species?
Give the group time to discuss and share with you their answer.
Set the requested level of nutrients and number of oyster platforms.
Ask the group: What does the bay looks like? Is the farm doing well?
Toggle underwater.
Ask the group: What did the water look like when nutrients was highest? What species were present? Did we succeed in balancing the Bay? Why or why not?
Discussion
5 min
Use the following questions to guide a discussion.
What do you think is essential for a healthy marine habitat? Ask students to give specific examples based on their observations.
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.