The conditions required for the successful cultivation of bull kelp (Nereocystis luetkeana) in Prince William Sound, Alaska, USA (PWS) are not well understood. PWS represents the northern most region of the species’ range. Growth, buoyancy, nutrient availability, salinity, and current exposure to better understand the requirements for cultivating this valuable and unique species.
Bull kelp was grown on modified 1 m x 1 m crab pots (kelp pots) threaded with 20 mm nylon strapping cord at the Native Village of Eyak’s Sheep Bay Research Farm. Five kelp pots were deployed in November 2023 at a water depth of 20-35 m. The pots were suspended by polyform buoys in the water column at a depth of 6 m. Bull kelp seed string was planted on four of the kelp pots in December 2023, while one control pot was left unseeded to compare buoyancy measurements due to biofouling. Another pot was designated for measuring kelp morphology by sacrificial means. Semi-monthly measurements of bull kelp morphology followed the Bull Kelp Research Squad working group’s standard operating procedures, which included measuring bulb + stipe length (BSL), stipe length, sub-bulb diameter, supra-holdfast diameter, mid-stipe diameter, and bulb diameter. Buoyancy measurements were conducted using a crane scale by weighing pots and kelp completely submerged in the water and also fully removed from the water. Additionally, an acoustic Doppler current profiler (ADCP), and HOBO water temperature loggers were moored at the site. Each field visit included CTD casts (RBR Concerto) and water quality sampling from 3 m depth to assess nutrient availability.
Presented here are data from the first year of a two-year study. Bull kelp morphology was not measured until April 2023 due to a lack of growth during the winter months. Water temperature and salinity did not significantly vary from past years’ data. Nutrient and current data analyses are pending. Anecdotally, bull kelp appeared nutrient starved based on the pale-yellow coloration of thalli. Sugar kelp grown nearby also displayed poor nutrient exposure with pale-yellow blades and transparent blade tips. From December 2023 to August 2024, bull kelp exhibited minimal growth. The peak average BSL was 51.7 ± 17.2 mm in June, with a density of 40.2 individuals m-1. The small size of the kelp prevented accurate buoyancy measurements due to the lack of sensitivity of the crane scale. By August, fewer than two ind. m-1 remained on the kelp pots.
A new crop of bull kelp will be seeded on the kelp pots in January 2025, and growth and buoyancy will be evaluated using the same methodologies to assess temporal variability.