CANOPY AND COMMUNITY STRUCTURE OF ROCKWEED BEDS IN NOVA SCOTIA AND NEW BRUNSWICK: REGIONAL VARIATION AND EFFECTS OF COMMERCIAL HARVEST AND PROXIMITY TO AQUACULTURE

Abstract

Ascophyllum nodosum (rockweed) is a significant component of intertidal rocky shore communities in Atlantic Canada. In Nova Scotia and Southwest New Brunswick, rockweed and other fucoids cover 80-90% of the intertidal zone, maintaining high biomass and primary productivity. Rockweed plays important roles storing carbon, cycling nutrients and providing habitat and food for associated plant and animal communities. For humans, rockweed has been economically important and commercially harvested in Atlantic Canada since the late 1950s. Considerable monitoring and research efforts have been made to study changes in rockweed plants themselves in response to harvesting; however, the effects of rockweed harvesting on the overall canopy structure and the associated fauna and flora have received much less attention. Additionally, the cumulative effects of harvesting and other human impacts, such as proximity to aquaculture, on the rockweed community have not been well studied. Using large-scale underwater field surveys and multivariate statistics, we quantified regional variation in the canopy and community structure of harvested and unharvested rockweed habitats in Southwest New Brunswick and Nova Scotia and established that canopy structure influences community structure. We conducted an experimental harvest reproducing the current commercial harvest in Yarmouth, Nova Scotia to assess the short-term effects of current harvest intensity. Finally, we demonstrate an effect of proximity to salmon aquaculture in Southwest New Brunswick that interacts with the effects of long-term rockweed harvesting on canopy and community structure. Overall, our results have implications for the spatial and ecosystem-based management of rockweed harvesting.