Exploration of Nereocystis luetkeana restoration in the Salish Sea: analysis of spore and gametophyte settled substrates to inform best techniques

Abstract

Canopy-forming kelp forests are vital to the marine environment, providing habitat and essential ecosystem services. However, Nereocystis luetkeana (bull kelp), the primary canopy kelp in the Salish Sea, has experienced significant declines in recent decades. Restoration efforts are urgently needed, but in this developing field, best practices are still being refined. In collaboration with Vital Kelp, a restoration company on the Sunshine Coast, this project evaluated and compared cultivation and out planting techniques. Two seeding methods (spore-settled and fragmented gametophyte sprayed) were applied to four substrate types: twine, clay tiles, green gravel, and polypropylene grid mesh. Successful settlement did not occur on the green gravel or clay tiles for either method. Kelp successfully settled on polypropylene twine and grid mesh, which were subsequently out planted at Ole’s Cove for further monitoring. Sporophyte recruitment was observed on the twine substrate for both seeding methods, but only the spore-settled grid mesh. This suggests that twine may be the most versatile and best substrate to work with. Additionally, performance of the seeding method may be influenced by the substrate type, with the gametophyte twine having a higher density and only the spore mesh exhibiting recruitment. However, none of these suggestions could be statistically concluded due to the limited dataset. Future kelp restoration efforts should prioritize exploring gametophyte-based approaches, as their potential for genetic preservation, selective breeding, and large-scale restoration, outweighs the benefits of traditional spore seeding methods.