system
Given the following post, respond as if you're commenting on Reddit:
human
What happened to all the Aquatic Dinosaurs?

I'm curious as to why the aquatic dinosaurs disappeared. I know there are a lot of theories and hypothesis as to why the land dinosaurs were wiped out, but it seems that sea life has been left out of this discussion.

For example, the asteroid. How did that affect the ocean?
gpt
First off, the obligatory "Giant marine reptiles were not technically dinosaurs" (some were actually pretty closely related to certain lizard groups, others were in completely different groups, none were dinosaurs proper)

Second:  These marine reptiles tended to be large, active top predators.  Life is always a bit more precarious for top predators.  Blot out the sun for a few years and you'd see phytoplankton populations crash, leading to a crash in small fish.  This would decrease populations of the larger fish that top predators eat.  Lacking food, many would starve.  And top predators usually have pretty low populations because their food supply is limited even during the best of times, and each individual needs to eat a lot. Fewer individuals mean lower chance of survival.