Kelp cheese is a food item that appears in the episode "Walking the Plankton."
It is dark yellow cheese.
Role in episode
It is one of the foods served on the cruise. The D'oeuvre guy offers some to Plankton, but the cheese lands on his head. Karen laughs at his misfortune and Plankton tells her that she should have married a pile of cheese, which gives Plankton an idea: he sculpts the kelp cheese into his likeness and sneaks off to steal the Krabby Patty secret formula.