Crown of Thorns starfish I

Crown of Thorns starfish I

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about what diagrams of food chains can and/or cannot tell you about the organisms involved. 
Scientists have observed the Crown of Thorns starfish eating hard coral and being eaten by fish such as wrasse, puffer fish and the triton trumpet shell fish.
They represent this feeding relationship in food chains as shown below.
COT-II-food-chain-400h.png
 

Question

The order of the organisms and the direction of the arrows are agreed upon by scientists to describe the feeding relationship [what eats what to obtain nutrition] between the species in a biotic community.
 

Choose which idea below is being represented by the direction of the arrows?

    • The energy transferred from one species to another.

    • The nutrients the predators obtain. 

    • The producer species. 

    • How much energy the predators need. 

Question

Choose which 2 things the Crown of Thorns food chain tells us about the hard coral?

    • Hard coral is eaten by the Crown of Thorns starfish.

    • Hard coral is eaten by zooplankton.

    • Pufferfish are a predator of hard coral.

    • Hard coral eats zooplankton.

Question

Feeding relationships can be very complex. Food chain diagrams tell just a little part of the food relationship story.
 
 
Choose which 2 things the Crown of Thorns food chain does not tell us about the Crown of Thorns predators?

    • Wrasse, pufferfish and triton trumpet shellfish are predators of Crown of Thorn starfish.

    • Wrasse, pufferfish and triton trumpet shellfish each eat the same amount of Crown of Thorn starfish.

    • Wrasse, pufferfish and triton trumpet shellfish only eat Crown of Thorn starfish. 

    • Wrasse, pufferfish and triton trumpet shellfish are not predators of hard coral.

Question 1Change answer

Knowing about the interactions of organisms in a food chain helps scientists predict what might happen when there is a change in the environment.
From the information in the Crown of Thorns food chain, for each of the following three statements choose whether you think scientists could confidently predict an outcome without gathering further information.
1. Overfishing of the triton trumpet shellfish will affect the COT starfish population 
confidently predictit dependscan't predict
2. A phytoplankton bloom [increase in the phytoplankton population] will affect the zooplankton population 
confidently predictit dependscan't predict
3. An increase in COT starfish will affect the hard coral population of a coral reef 
confidently predictit dependscan't predict

Question

Choose one of your answers and explain why you think this.

    • Overfishing of the triton trumpet shellfish will affect the COT starfish population

    • A phytoplankton bloom [increase in the phytoplankton population] will affect the zooplankton population

    • An increase in COT starfish will affect the hard coral population of a coral reef 

Explanation
Task administration: 
This task can be completed with pencil and paper or online.
Level:
5
Curriculum info: 
Science, Communicating in science, Living World
Keywords: 
food chains, starfish, feeding relationships, scientific explanations
Description of task: 
Task: Decide what information can or cannot be inferred from food chain diagrams. Assessment focus: reading food chains
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.  
 
Capability: Use evidence
This resource provides opportunities to discuss what/how much evidence is needed to support an explanation.
 
Capability: Interpret representations
This resource provides opportunities to discuss scientific conventions for representing feeding relationships (a food web).
Science capabilities: 
Interpret representations, Use evidence
Answers/responses: 
Questions
Choose which idea is being represented by the direction of the arrows.
Responses
  • The energy transferred from one species to another.
Choose which 2 things the Crown of Thorns food chain tells us about the hard coral.
  • Hard coral is eaten by the Crown of Thorns starfish.
  • Hard coral eats zooplankton.
Choose which 2 things the Crown of Thorns food chain does not tell us  about the Crown of Thorns predators.
  • Wrasse, pufferfish and triton trumpet shellfish each eat the same amount of Crown of Thorn starfish.
  • Wrasse, pufferfish and triton trumpet shellfish only eat Crown of Thorn starfish. 
From the information in the Crown of Thorns food chain, for each of the following three statements choose whether you think scientists could confidently predict an outcome without gathering further information.
 
  1. Overfishing of the triton trumpet shellfish will affect the COT starfish population.
  2. A phytoplankton bloom [increase in the phytoplankton population] will affect the zooplankton population.
  3. An increase in COT starfish will affect the hard coral population of a coral reef.
Accept any answer for each of the statements. Evidence should support student's choice. 
Students might look at the short term:
one change e.g., 
  • With fewer triton trumpet shellfish eating the Crown of Thorn starfish the COT numbers could increase.
  • More COT starfish could eat more of the hard coral so the hard coral numbers could decrease.
Students might look at the long term:
more than one change e.g., 
  • As phytoplankton numbers increase zooplankton, which feed on the phytoplankton, could increase. As zooplankton increase, predators that eat the zooplankton could also increase. 
Or changes that eventually restore the system to a balance/equilibrium, e.g.,
  • With fewer triton trumpet shellfish other predators may increase in numbers as they have more food. As the predator population increases the COT starfish numbers decrease. With less food the predator population could then decrease. Eventually the predator population and the COT starfish populations reach a stable number where both populations are able to survive.   
Students that answer it depends might ask questions, e.g., 
  • We don't know how much COT starfish, triton trumpet shellfish eat so we can't be sure of their effect on the COT population.  
  • Does anything else eat the hard coral? If COT starfish populations increase other predators of the hard coral might have less to eat so their population may decrease. Overall the total number of predators eating the hard coral might not change so the hard coral population may not be affected.
Diagnostic and formative information: 
Questions Problems/Misconceptions
Choose which idea is being represented by the direction of the arrows.
Most students who answered incorrectly chose:
The nutrients the predators obtained 
 
Next steps:
Discuss that the arrows go that way because scientists wanted to show the direction of energy transfer and this was the convention they agreed on. 
From the information in the Crown of Thorns food chain, for each of the following three statements choose whether you think scientists could confidently predict an outcome without gathering further information. 
  • Overfishing of the triton trumpet shellfish will affect the COT starfish population.
  • A phytoplankton bloom [increase in the phytoplankton population] will affect the zooplankton population.
  • An increase in COT starfish will affect the hard coral population of a coral reef. 
Most of the students answered that they could confidently predict an outcome without gathering further information. These students were focused on the immediate effect of removing a predator or increasing the food supply e.g., 
 
With no predators, the hard coral can live longer and produce more coral babies and increase the population.
 
Because zooplankton feed off phytoplankton so if there is more phytoplankton there will be more zooplankton becasue there is more food.
 
Others gave more connections. They were beginning to show long term effects and how all the organisms in a system are affected by a change, e.g.,
 
The more COT starfish there are, the less hard coral resulting in more zooplankton and thus less phytoplankton.
 
more COT means more food for predators meaning back to equilibrium.
Based on a sample of 38 students completing the task on-line. 
Next steps: 
Science Capability: Interpret representations
Scientists use representations to tell us about an idea, an object, a process or a system. They are often 'limited' representations of the particular idea or 'thing' that is being talked about. A food chain diagram is a limited representation of an organism's feeding relationship. 
 
To understand the limitation of representations teachers could ask students to consider what the food chains or food webs tell us and what is left out. As in the Cockles resource they could also:
  • research one of the organisms in a food web and list all the things they eat; and/or
  • include another of their food sources into the food web with the connections to other organisms in the food web that also eat this food.
The following Level 5 ARB resources are about food chains: