Graduation Date

Spring 2023

Document Type



Master of Science degree with a major in Natural Resources, option Fisheries

Committee Chair Name

Rafael Cuevas Uribe

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Jose Marin Jarrin

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Frederick Zechman

Third Committee Member Affiliation

HSU Faculty or Staff


Seaweed, Aquaculture, Humboldt Bay, Seaweed farm, Pacific dulse, Devaleraea mollis, Long lines, Long-lines, Pacific Northwest

Subject Categories



The goal of this study was to adapt open-water rope culture techniques to the native red seaweed Devaleraea mollis to support a new seaweed aquaculture industry in Humboldt Bay, California. The specific objectives for this study were to: 1) evaluate the growth of D. mollis cultivated at different depths and seasons (fall/winter, spring/summer), 2) estimate nutrients removed by D. mollis from the water, and 3) measure heavy metals and pesticides to determine potential health risk upon ingestion. Bundles of seaweed were inserted into 3 m long weighted vertical lines attached to two horizontal long-lines suspended by floats. Two four-month trials (September to December 2020 and April to July 2021) were compared. Long-lines in Trial 1 were seeded on the same date, and data was pooled from both long-lines. Data was analyzed separately for each long line in Trial 2 as the lines were seeded on different dates. Both depth (p<0.001) and month (p<0.002, two-way ANOVA, Tukey HSD test) had significant effects on wet weight for the first trial with depths 0 m and 1 m and months November and December producing the best growth. For Trial 2 only depth was significant (p=0.006) for long-line 1 with the 0 m depth producing the best growth while both depth (p<0.001) and month (p=0.006) significantly affected wet weight for long-line 2 with 0 m and the month of May producing the best growth. Maximum growth rate from Trial 1 was 0.21 g/day, and 0.19 g/day from Trial 2. A total of 1.20 kg of carbon, 0.12 kg of nitrogen, and 0.02 kg of phosphorus were removed from the water by the seaweed produced in this study. All pesticides were found to be undetectable, and all heavy metals were either undetectable or below action levels with the exception of manganese for 3 m in Trial 1 and 2 m and 3 m in Trial 2 (21.0 mg/kg, 77.6 mg/kg, 93.3 mg/kg respectively). Results from this study suggest optimal growth occurs in the winter and early spring at no more than 1 m in depth, D. mollis’s potential for nutrient bioextraction, and that D. mollis grown in Humboldt Bay poses low risk to consumers for heavy metals and pesticides.

Citation Style

Aquaculture Journal


Thesis/Project Location


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