We have critters in the ocean that would die without petrochemicals to eat. The oil bubbles up from naturally occurring deposits.
In vietnam, off the Mekong delta, the USS Iwo Jima's Avgas fuel cells were invaded by a microbe that turned the purple 115/145 avgas brown. They were eating high octane leaded gas. These fuel cells had to be purged and disinfected at Sasebo, Japan. This gave me a month of virtual R&R in Subic Bay while we waited for the ship to return.
Want to see petrochemical microbes at work? Add a tablespoon of water to a gallon of diesel fuel and watch it turn into sludge.
There is a broad spectrum of life that is dependent on hydrocarbons and able to metabolize it into an even broader spectrum of other chemicals.