So long and I suppose I should start putting names to things so I guess I'll call the stuff I've been eating ehh plankton that's a fine name init so eh so long and thanks for all the plankton
'So long and thanks for all the fish!' is what the dolphins say in the Hitchhiker's Guide to the Galaxy, when they leave the Earth and fly off into space, shortly before the Earth's destruction to make way for a hyperspace bypass.
The Purrgil's in Star Wars are also a species of space-faring cetaceans and OP is making a meme linking the two.