I'm developing a planet populated by giant sea creatures (think Megalodon, but bigger.) While I know that gravity has an effect on size, the sources I found only made reference to land creatures, who can't grow past a certain size, or else their legs/bones would snap. Legs are obviously not a problem for sea creatures.
What things determine the upper size limit on aquatic creatures? How much effect does gravity have on aquatic size? Or is size more a function of available food (which is what I've heard about blue whales)?
(First-time asker, so if I've done something wrong, please let me know and I'll do better next time!)