In 2019, with the collaboration of Karen Gray and GreenWave and with support from the California State University Agricultural Research Institute, Cal Poly Humboldt (then known as Humboldt State University) established the first commercially licensed seaweed farm in open water in California. The university’s seaweed farm is located in a one-acre leased area in Humboldt Bay (Wiyot: Wigi), CA. This bay is unique because it is managed by the Humboldt Bay Harbor, Recreation, & Conservation District, which was able to secure the permits necessary to grow seaweed. Lacking prior knowledge of which species to grow, when to grow them, how to grow them, and what yield to expect, we decided to investigate these factors further.
In August 2020 (during COVID-19), we installed two 107-m long-lines. Pacific dulse (Devaleraea mollis) was the first seaweed we outplanted. We used 3-m droppers to evaluate the growth of dulse at 0, 1, 2, and 3 m. We found that the best growth was at 0 and 1 m and the best months were May, November, and December. Bull kelp (Nereocystis luetkeana) was the second species outplanted. In October 2021, we installed a multi-line system (five 60-m grow lines) along a depth gradient to evaluate kelp growth at different depths. Unfortunately, our first attempt to grow bull kelp was impacted by record-high precipitation levels in January 2023. This caused Humboldt Bay to become brackish, with salinity levels as low as 27 ppt (Figure 1). On the second attempt, we outplanted seedlings in March 2023 and harvested in June 2023. We produced as much as 6 kg per meter of bull kelp on the single-line systems.
Winged or ribbon kelp (Alaria marginata) was the last species we tested. For the outplants in July 2024 and June 2025, none of the sporophytes survived due to high temperatures in the bay (up to 19°C). When the seedlings were outplanted in December 2024 and harvested in April 2025, we were able to produce as much as 2.2 kg per meter.