Why cant an ecosystem exist without producers

The producers produce glucose and that is the source of energy for all life. Most producers are plants, which harness the sun's energy, however deep in the ocean near volcanic vents, there are producers that use chemical energy to make glucose.

Producers convert basic energy from the sun or in some cases, chemicals or heat vents, and turn it into usable energy, hence the name "producers". Without that, other creatures would starve.