In a closed ecosystem, red algae, crabs and green algae are present and interact with each other. In order to understand the interactions between them, the following experimental treatments were imposed
i. All crabs removed
ii. All green algae removed
iii. All crabs and green algae removed
iv. All crabs, red and green algae are retained (Control)
The results of red algae growth from these experiments are shown in the graph. Plus $(+)$ indicates presence and minus ( - ) indicates absence in this closed ecosystem. Red algae growth in all the treatments was significantly different from each other.


Based on these results, the correct option is

• A

  in the absence of crabs, green algae positively affected red algae growth.
• B

  in the presence of crabs, green algae positively affected red algae growth.
• Correct answer
  C

  in the absence of green algae, crabs negatively affected red algae growth.
• D

  in the presence of green algae, crabs negatively affected red algae growth.

Hence, the correct answer is option: 'C'.