Answer:
Zooplankton
Explanation:
The correct answer here would be the zooplankton. (see the attached image)
Due to the important position of the Zooplankton in the food web, any change in the environment that removes them will cause the most instability in the ecosystem.
Five different organisms within the food web directly depend on the zooplankton for their food four of which have no any other option. Removal of zooplanktons from the environment will directly affect these organisms and this will throw the entire food web into disarray.
