Changes in composition of rockweed (Ascophyllum nodosum) beds due to possible recent increase in sea temperature in Eastern Canada

Abstract

Ascophyllum nodosum (rockweed) is the main economic resource of the seaweed industry in the Atlantic Provinces of Canada. The annual harvest steadily increased since 1995, reaching a historic peak of 37,000 tonnes in 2007. Due to a high demand for fertilizers and animal feed supplements derived from rockweed, this trend seems likely to continue. The current management plan for the sustainable harvest of the A. nodosum resource is considered conservative. The resource has been managed with a precautionary approach since 1995 to protect the integrity of the habitat. Acadian Seaplants Limited (ASL) has been granted approximately 90% of the government-issued licenses to harvest A. nodosum resources in the Maritimes. The Canadian approach is based on an annual harvest from a given bed and not strip-and-return after several years. Since 1995, ASL has proactively undertaken extensive annual surveys and research on biomass productivity of this renewable resource to establish acceptable annual exploitation rates. Historically, the rockweed beds of southwestern Nova Scotia (NS) have been almost 99% pure A. nodosum, with a minor component of Fucus vesiculosus. However, since 2004, a steady increase in F. vesiculosus, with a peak of 4.6% of the total biomass in 2008, was recorded. This coincided with one of the mildest winters on record for the Maritimes. This increase in temperature seemed to be also responsible for an unusual recruitment of the blue mussel Mytilus edulis in rockweed beds in some areas of southern New Brunswick (NB) in 2006, causing the detachment of up to 30% of the seaweed biomass in some harvesting sectors. Another phenomenon observed in southwestern NS during 2003 and 2004 was extensive ice damage on rockweed beds produced by an early melting of the ice, with losses of up to 90% of the rockweed biomass in some areas.