Problem 10 - Campbell Biology

Question

In the Chesapeake Bay estuary, the blue crab is an omnivore that eats eelgrass and other primary producers as well as clams. It is also a cannibal. In turn, the crabs are eaten by humans and by the endangered Kemp's Ridley sea turtle. Based on this information, draw a food web that includes the blue crab. Assuming that top-down control occurs in this system, describe what would happen to the abundance of eelgrass if humans stopped eating blue crabs.

Step-by-Step Solution

Answer

Eelgrass abundance will likely decrease.

Step 1: Identify Organisms

List all the organisms involved: eelgrass, blue crabs, clams, humans, and Kemp's Ridley sea turtles.

Step 2: Establish Trophic Levels

Identify the trophic levels: - Primary producers: eelgrass and other primary producers.- Primary consumers: blue crabs (when eating eelgrass).- Secondary consumers: blue crabs (when eating clams), humans, and Kemp’s Ridley sea turtles.

Step 3: Draw the Food Web

Create a diagram with arrows pointing from the food source to the consumer:- Eelgrass → Blue crab- Clam → Blue crab- Blue crab → Human- Blue crab → Kemp's Ridley sea turtle- Blue crab → Blue crab (cannibalism)

Step 4: Analyze Top-Down Control

Top-down control occurs when predators control the structure or population dynamics of the ecosystem. Because humans are predators of blue crabs, if humans stop eating blue crabs, the crab population will likely increase.

Step 5: Predict Eelgrass Abundance

With an increase in blue crab population, there will be more blue crabs eating eelgrass, which will likely lead to a decrease in eelgrass abundance.

Key Concepts

Chesapeake Bay estuary

The Chesapeake Bay estuary is an incredibly diverse and vital ecosystem located on the East Coast of the United States. Estuaries are unique because they are areas where freshwater from rivers mixes with saltwater from the ocean, creating a diverse habitat for many species. The Chesapeake Bay supports thousands of species, including fish, birds, and plants. It also provides essential resources and services such as water filtration, storm protection, and breeding grounds for fish and shellfish. Understanding this estuary is crucial for managing and maintaining its health and biodiversity.

Trophic levels

Trophic levels are the hierarchical steps in a food chain, where each level represents a different position in the flow of energy or nutrients. Here's a simple view:

• Primary producers: These are plants, algae, and other organisms that produce their own food through photosynthesis. In our exercise, eelgrass and other primary producers fit this category.
• Primary consumers: These organisms eat primary producers. Blue crabs, when they consume eelgrass, are primary consumers.
• Secondary consumers: These organisms eat primary consumers. Blue crabs, when eating clams, humans, and Kemp’s Ridley sea turtles all fit into this level.

This layered structure helps us understand how energy flows through an ecosystem and how different organisms are interconnected.

Top-down control

Top-down control refers to a scenario in which predators at the top of the food chain regulate the population sizes of the organisms below them. In the context of the Chesapeake Bay estuary, humans act as top predators by consuming blue crabs. If humans stopped eating blue crabs, the population of blue crabs would increase because there's one less predator keeping their numbers in check. This increase would lead to more blue crabs consuming eelgrass, ultimately reducing the eelgrass population. Top-down control showcases how changes at the top of the food web can cascade down and affect the entire ecosystem.

Ecosystem dynamics

Ecosystem dynamics involve the natural changes and processes that occur within an ecosystem. Factors like predation, food availability, and environmental conditions continuously shape these processes. In the Chesapeake Bay estuary, the interaction between blue crabs, clams, eelgrass, and the Kemp's Ridley sea turtle is a perfect example of complex ecosystem dynamics. Changes in one species, such as an increase or decrease in the blue crab population, can lead to significant effects across the entire food web. For instance, if blue crab numbers rise, eelgrass abundance may decline, which could then affect other species that rely on eelgrass for habitat or food. Understanding these dynamics helps in making informed decisions for conservation and resource management.