Spatial and temporal variability of carbohydrate compositions in cultivated Alaria marginata, Nereocystis luekteana, and Saccharina latissima

Abstract

Carbohydrates derived from Laminariales (kelp), including polysaccharides and sugar alcohols, present significant market opportunities for nascent mariculture industries. These carbohydrates can enhance crop biomass value through extractive processing, with applications in medicine, manufacturing, health supplements, and bio-plastics. The relative abundance and composition of carbohydrates in kelp can vary depending on species, life history, tissue type, season, and environmental conditions. In Alaska, mariculture of kelp focuses on three species: Alaria marginata, Nereocystis luetkeana, and Saccharina latissima. This study assessed the relative abundance of carbohydrates (glucan, mannitol, alginate, and fucoidan) in these species, as well as the sulfate content of fucoidan and the ratio of mannuronic to guluronic acids in alginate (M:G ratio) as proxies of chemical attributes for these carbohydrates. Samples were collected from commercial farm sites in the Kodiak Archipelago, Prince William Sound, and Southeast Alaska between April and June of 2023. Carbohydrate composition was analyzed using high- performance anion-exchange chromatography with pulsed amperometric detection. Composition varied among species, where on a dry mass basis, A. marginata had the highest average contents of fucoidan and alginate, while S. latissima had the highest average glucan content. Fucoidan was the only measured component to have consistent trends over time across sites for all species. Inconsistency in trends over time across sites for biochemical components was most notable in A. marginata. Seawater temperature was the most consistent environmental predictor across species, having a moderate, negative correlation the M:G ratio in all species and a moderate, positive correlation with fucoidan in A. marginata and S. latissima. Of the species studied, S. latissima harvested in June may have the highest potential for extractive processing in Alaska. This species had a balanced composition of valuable carbohydrates, high consistency across sites, and high potential yield from a relatively large fraction of solids in wet biomass combined with generally high wet mass growth. This study highlights the complex variability of carbohydrate compositions in kelp and provides the first detailed assessment of A. marginata, N. luetkeana, and S. latissima in Alaska.