What happen if photosynthetic protists disappeared from ocean, how would it affect the food chains in the ocean?

We'll see mostly ever marine life depends on plants in the ocean for example shrimp eat the sea grass and a fish eat that shrimp then a bigger fish eats the fish next a seal eat the fish then a shark eats the seal and sadly my poor sharks are becoming extinct humans evil people hunt them slice up their fins and throw them back in the ocean alive to slowly die
Please save the shark and recycle to keep plastic out of are oceans