Bull kelp is a large annual brown seaweed (Nereocystis luetkeana) of the Pacific Northwest, named for the whip-like stem and hollow, cannonball-sized float that keep its blades near the sunlit surface. Firm and crunchy rather than silky, it is eaten fresh and — most famously — brined and pickled, its thick stipe sliced into rings for tangy relishes, salsas and ceviche-style dishes along the coasts of Washington, British Columbia and Alaska.