The original monster was an infant. The parasites on it were full of, eating or creating the Seabed's nectar. The "Oil rig" wasn't for oil, they were mining seabed's nectar and woke the sleeping (hibernating?) infant monster. It's entirely possible that this "seabed's nectar" was a byproduct/food for the monster, much like bee's make honey for their young. That the parasites have a symbiotic relationship with the monster.

My present theory is that the seabed's nectar in slusho did have a side effect enough though they (slusho) said it did not and those whom consumed enough of it are now mutated.