Does bryozoan colonization alter the biochemical composition of Saccharina japonica affecting food safety and quality?

The encrusting bryozoan Membranipora membranacea frequently colonizes late-harvested blades of the cultured Saccharina japonica. We measured the proximate compositions, amino acid and fatty acid profiles and metal contents of bryozoans, colonized blades and healthy blades. Bryozoans contained high levels of crude ash (657 g kg-1 dry weight) and arsenic (As; 49 mg kg-1 dry weight) contents, exceeding the recommended range for human food, and had relatively low levels of essential amino acids. The content of inorganic As in bryozoans was 31% of the provisional tolerable weekly intake for inorganic As established by the World Health Organization. Hence, bryozoans decrease the food and fodder quality of the seaweed product. After removing the bryozoans, we found that the seaweed blade tissues beneath the colonies had elevated levels of potassium, iodine and docosahexaenoic acid and reduced levels of copper, chromium and cadmium compared to healthy tissues. Thus, lacy crust bryozoans must be removed from the surface of seaweed prior to its use as food or fodder.