Answer:
It would prevent them from receiving sunlight and, therefore, to produce photosynthesis, affecting the amount of atmospheric oxygen and disrupting the food web.
Step-by-step explanation:
Diatoms are a group of microalgae that are important components of phytoplankton, which produce almost half of atmospheric oxygen and are the base of the marine food web.
If diatoms weren't able to store their food as oil, it would prevent them from receiving sunlight and, therefore, to produce photosynthesis as the oil enables them to float in the sea surface. This situation would have detrimental impacts on the food web because, as primary producers, they are fundamental organisms that not only provide oxygen for the marine ecosystem and the atmosphere but they also serve as food for zooplankton, which are then eaten by bigger and important organisms.