i hope this answers your question.
no
Phytoplankton is the small plant life that whales and some other sea life eat. Many other forms of sea creatures eat fish and other sea creatures.
Large creatures live in the ocean, eat other animals, and get eaten by other animals. (example: Sea Turtles eat Jellyfish)
Some sea creatures have ansetors of dinosaurs
Some plants eat plankton and other small creatures.
If you mean, "are all under water creatures, sea creatures?" then no. The term SEA is for the ocean and there also can be creatures in freshwater. Also some creatures that live in water such as some snakes and sea turtles come out of the water every so often, so they are no total sea/water creatures. Fish are underwater creatures though.
Some people believe in Champ and Nessie.they are related sea monsters.
sea stars mainly, and some other sea creatures that eat away at the coral reef
Any sea creature, from the blue whale to the smallest krill, will be eaten by other creatures when they die.
Yes every day by other deep sea creatures.
some
None, all sea creatures eat each other if no food .
They feed on fish and other small sea creatures.