You are presented with the question "What are a source of food for many fish species?" and the following answer choices: 
- layers of fat
 - bird species
 - human species
 - keystone species
 - Organic compounds
 - barnacles
 - gastropod shells
 - species of deer

Now knowing that sponges are a source of food for many species of fish and sponges are also keystone species, choose the best answer.


 

    keystone species     