Bull Kelp Buoyancy Assessment

Kelp farm anchoring systems are the most important and expensive component of a farmer’s investment. Balancing costs and efficacy for each unique farm site and species cultivated is critical for the sustainable growth of this industry. Growing bull kelp (Nereocystis luetkeana) adds additional hurdles to anchoring designs due to the buoyancy of its characteristic floating pneumatocysts. A lack of information regarding the buoyancy of an entire crop of bull kelp and how this changes during the growing season has made designing appropriate anchoring systems difficult. The objective of this project is to fill this data gap and understand how cultivated bull kelp buoyancy changes during growth at an exposed location in the Prince William Sound (PWS). We propose a straightforward study design to document changes in bull kelp buoyancy over the course of a year. Bull kelp seeded crab pots will be suspended in the water column at 10 m throughout the study. These arrays will be monitored for kelp density and individual morphology (pneumatocyst diameter, stipe length, biomass) and compared to a control array without seed string. Oceanographic conditions including temperature, salinity, and currents will be documented via instrumentation (CTD, temperature loggers, ADCP). Additional measurements of individual bull kelp plants grown on NVE’s established MacroAlgal Cultivation Rig (MACR) will be sacrificed monthly to determine buoyancy of each. The results from this study will fill a critical data gap required by engineers to design cost-effective anchoring systems that can maintain this floating kelp throughout its life cycle.

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