Kwakwaka’wakw use of the edible seaweed łәqq’әstәn (Porphyra abbottiae Krishnamurthy: Bangiaceae) and metal bioaccumulation at traditional harvesting sites in Queen Charlotte Strait and Broughton Strait

Abstract

Porphyra abbottiae Krishnamurthy (Rhodophyta) is an intertidal red alga harvested by a number of coastal First Nations in British Columbia. The Kwakwaka’wakw have a long history of harvesting P. abbottiae as food and medicine, reflected in the language, songs and stories of the Kwakwaka’wakw oral tradition. Harvesting and drying practices for this alga have undergone changes with the introduction of new technologies and a decrease in time available for seaweed harvesting. The adoption of timesaving equipment into the seaweed harvest has given harvesters the flexibility to work around constraints including work and school obligations, tides, long distances to harvesting sites, and unpredictable weather conditions. Harvesting and drying practices reflect a thorough understanding of the lifecycle, biology, and ecology of P. abbottiae. Timing of the harvest during the seasonal round optimizes the taste and texture of P. abbottiae fronds while avoiding the seaweed in its reproductive stage. Songs and taboos associated with the harvest promote safety and efficiency while harvesting the seaweed.

Concerns about potential contamination of edible seaweed led to the second part of this research: testing for metal contamination. Inductively coupled plasma mass spectrometry analysis for selected metals and trace elements revealed the presence of arsenic, cadmium, lead, and mercury in Porphyra abbottiae sampled from the southern Queen Charlotte and Broughton Straits. Mercury concentrations fell below the detection limit of 0.01 ng/mL in 28 of 112 samples. Calcium was the most abundant element measured, averaging 1445 mg/kg dry seaweed. The remaining metals, in decreasing order of concentration, are: Fe>As>Zn>Mn>Cu>Cd>Pb>Cr>Co>Se>Hg. Copper-zinc (r=0.835) and copper-lead (r=0.948) concentrations are significantly correlated (p<0.05), suggesting selective uptake of these elements. PCA analysis suggests that the location of harvesting sites within specific water channels is influencing metal concentrations. Hazard quotients calculated using guidelines set by Health Canada and the World Health Organization revealed that, among the suite of elements surveyed, arsenic followed by cadmium ranked the highest in relative risk for consumers of P. abbottiae. An average 60 kg adult consumer can safely consume approximately 9.4 g dried seaweed per day and not exceed tolerable upper intake limit guidelines. In conclusion, Porphyra abbottiae can be eaten in moderation with minimal risk of chronic metal contamination. Kwakwaka’wakw consumers can also benefit from cultural reconnection with this important traditional food.