Every trophic level in a food web is important because each level depends on the level below it for food energy.
The producers or autotrophs, which include green plants and algae, capture solar energy and transform it into the chemical energy found in food, such as glucose sugar. They do this by carrying out photosynthesis--chemically combining water and carbon dioxide in the presence of light energy to produce glucose sugar plus oxygen.
The removal of the producers would cause the collapse of the entire food web. Primary consumers or herbivores, which feed on producers directly, would die off. The next to be affected would be the secondary consumers or carnivores that eat the primary consumers. Higher level consumers would suffer as organisms from lower trophic levels start to die off. Decomposers would break down the bodies of dead organisms, returning their basic elements and compounds to the environment. However, even these dead organisms would run out and the entire food web would collapse.
To conclude, in a food web, the removal of any trophic level upsets the balance within the web and can cause its eventual collapse. Because producers capture solar energy and convert it to food energy, their loss would affect every other level of the food web.
I have attached a link with a great diagram of a food web in Chesapeake Bay.