About Bull Kelp

Photo Credit: Angie Korabik

Bull kelp (Nereocystis luetkeana) is a canopy forming species of kelp native to the North American west coast. The range of bull kelp extends from Point Conception (California, USA) in the south to the Aleutian Islands (Alaska, USA) in the north (Abbott & Hollenberg 1992). Bull kelp typically grows in nearshore subtidal environments at depths between 10-100 feet, and is particularly adapted to coastlines characterized by high wave action. Bull kelp is typically thought of as an annual species, with yearly canopy reappearances and die offs, but in some areas (e.g. Kodiak), bull kelp canopies overwinter and can be found all year round.

Bull kelp is an ecologically and culturally important species. Bull kelp canopies create ecosystems and food supplies for a number of ecologically and economically important species such as urchins, abalone, cod, salmon, and even other seaweeds. Additionally, bull kelp canopies provide a number of benefits to humans, such as a source of food, a good fertilizer, and reducing coastal erosion via wave dampening.

Bull kelp can grow up to 33 meters (>100 feet) in height, and at peak growth, can grow up to 6 inches per day. Bull kelp’s physical structure can be divided into 4 main sections:

The holdfast - the root-like structure that anchors kelp to rocks
The stipe - the stem like structure that reaches towards the surface
The pneumatocyst (or bulb) - the round, gas filled structure that reaches the water surface and causes bull kelp to float, and
The blades - the leaf-like structures that photosynthesize near the surface of the water.

Photo Credit: BKRS SOP

Bull kelp’s life cycle alternates between two main stages: the large, sporophyte (what we typically imagine when we think of kelp) and the microscopic gametophyte. As they grow, sporophytes develop patches called sori at the end of their blades. These sori contain millions of spores that are eventually released into the water column, either at the surface or at the benthos once the sorus is abscised (dropped) and sunk to the bottom. These spores will eventually sink and settle onto hard surfaces where they will develop into either male or female gametophytes (A). Females will begin to extrude eggs and release a pheromone called Lamoxirene that stimulates sperm release from the males. Once fertilization occurs, the newly fertilized eggs will begin to grow tiny blades (B) that eventually grow into a new adult sporophyte.

Photo Credit: A) Angie Korabik B) Tamsen Peeples