Biomass and height of Ascophyllum nodosum after two decades of continuous commercial harvesting in eastern Canada

With the increasing demand for seaweed resources worldwide, management must ensure that the harvest of wild seaweed stocks is sustainable. We evaluate the impact of over 25 years of commercial harvesting of Ascophyllum nodosum in eastern Canada by comparing the biomass and height of the seaweed in the late 1990s to the late 2010s over a broad spatial scale spanning the provinces of Nova Scotia and New Brunswick. There has been no significant decrease in the biomass of A. nodosum in either province, and biomass has increased in some regions of New Brunswick during that period. The average height of A. nodosum has decreased by 7.8 cm in Nova Scotia while it increased by 13.8 cm in New Brunswick. Biomass of A. nodosum in unharvested sectors was 7% higher than that in harvested sectors while height of A. nodosum in unharvested sectors in New Brunswick is similar to the values observed in harvested sectors. Over the same period, water temperature has increased in both provinces and, in recent years, has at times exceeded the optimal growing temperature for A. nodosum within bays in Nova Scotia. We conclude that the current management and harvest of A. nodosum in eastern Canada are sustainable and maintain the biomass and height of A. nodosum beds but that control sites are necessary to offer adequate comparisons as environmental conditions are changing.

Automated summary

The study evaluated the impact of over 25 years of commercial harvesting of Ascophyllum nodosum in eastern Canada by comparing biomass and height. It was found that there was no significant decrease in biomass, and in some regions, there was an increase. While the average height of A. nodosum decreased in Nova Scotia, it increased in New Brunswick. In unharvested sectors, biomass was higher, but height was similar in harvested and unharvested sectors in New Brunswick.