Variation in biochemical composition of wild-harvested Macrocystis pyrifera (Ochrophyta) from sites proximal and distal to salmon farms in Tasmania, Australia

Macrocystis pyrifera (Linnaeus) C. Agardh (Ochrophyta), also known as giant kelp, is a key species in coastal ecosystems of temperate regions worldwide providing important habitats and food for a range of species. M. pyrifera also has the potential for cultivation for commercial application (e.g. food, food additives and feed). This study compared the effect of proximity to Atlantic salmon aquaculture sites (proximal and distal) on the nutritional value (proximate composition, fatty acids, and dietary minerals) and metal profiling of wild M. pyrifera populations applying standard procedures for proximate composition (Kjeldahl procedure with N x 5 for protein, cold extraction using dichloromethane: methanol (2:1) for lipid, oven drying for moisture, incineration in a muffle furnace for ash, and carbohydrate content calculated by difference), esterification for fatty acid and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for minerals and metals. Lipid contents and some fatty acids (FA, e.g. polyunsaturated fatty acids (PUFAs)) were higher in samples proximal to salmon farms; however, concentrations of lipids were low overall (<1.5% of dry weight). Moisture was consistently higher in distal samples, while the effects of proximity to salmon cages on the concentrations of protein, ash, and carbohydrates (as nitrogen-free extract) were not consistent amongst regions. Iodine levels did not vary between proximal and distal samples, while differences were reported for other elements between the investigated sites, particularly for phosphorous, iron, sodium, and potassium. Overall, metals including aluminium, arsenic, lead, cadmium, and mercury, were low and do not represent a concern for human consumption. These findings help to understand the potential of farming M. pyrifera in combination with finfish aquaculture in southern Australia for nutrient remediation from the finfish aquaculture, and aid in identifying possible commercial applications for M. pyrifera in the Australian market, including food, feed, fertiliser, and nutraceuticals.

Automated summary

Macrocystis pyrifera, also known as giant kelp, is a key species that provides important habitats and food for various species in coastal ecosystems worldwide. This study compared the effect of proximity to salmon aquaculture sites on the nutritional value and metal profiling of wild M. pyrifera populations. The results showed that lipid contents and some fatty acids were higher in samples near salmon farms, while moisture content was higher in distal samples. The concentrations of protein, ash, and carbohydrates varied inconsistently with proximity to salmon cages. Metal levels were low and not a concern for human consumption. These findings help understand the potential of farming M. pyrifera in combination with finfish aquaculture and identify possible commercial applications in the Australian market.