Kombu is kelp, which means it grows exclusively in saltwater. On the other hand, nori algae is a seaweed that can grow in oceans, rivers, or lakes. In some recipes, nori works as an excellent substitute for kombu. For instance, both kombu and nori will work well in this Sushi Bowl recipe. However, the lack of umami flavor and soft texture of nori will not work in noodle broths and stocks.