Repetitive harvesting of Macrocystis pyrifera (Phaeophyceae) and its effects on chemical constituents of economic value

Kelp harvesting has increased globally in recent decades and is expected to continue rising as the demand for kelp-derived products for use in aquaculture and industrial applications increases. In response, numerous studies have examined how harvesting impacts kelp populations and their associated communities, but the effects of repeated harvesting of the same individuals on the chemical properties for which they are extracted remain poorly understood. This knowledge gap may be especially crucial in areas where the same kelps are necessarily harvested multiple times per year due to their overall low abundance. To address this, we examined how repetitive harvesting of the same individuals of giant kelp, Macrocystis pyrifera, over a 3-month period influences tissue chemical properties (i.e. alginate yield, viscosity and strength, nutritional quality, such as protein, carbohydrate, lipid, crude fiber, ash and energy content, and tissue carbon/nitrogen ratios). Our results indicate that, while these properties vary over time, presumably due to variability in oceanographic conditions, repetitive harvesting of the same individuals does not significantly impact these properties.