This spell costs {1} less to cast for each Sea Creature you control with a +1/+1 counter on it.

Sea Creature spells you cast cost 1 less to cast for each Sea Creature you control.

(Krakens, Serpents, Leviathans, Whales, Crabs, Squid, Starfish, Turtles, Fish, and Octopuses are Sea Creatures)