Marie is an Octoling, so it's technically not cannibalism.

My interpretation of the image is that the takoyaki belongs to Marina and she is trying to prevent Pearl from putting her disgusting condiment on it.

Either way squid and octopus are both sapient creatures in this universe so eating each other should be frowned upon.

and now I remember Marie saying that squid rings were morbidly delicious, so I don't know anymore.