Recovery Following Harvesting of Ascophyllum nodosum Forests: Impacts on Populations and Canopy Composition

ABSTRACT

Our overall aim was to assess the sustainability of exploitation of slow‐growing, long‐lived intertidal Ascophyllum nodosum forests. They have been mechanically harvested for almost 50 years in Breiðafjörður, Iceland, but there is a lack of long‐term local research as various local factors can impact the recovery time of Ascophyllum. Post‐harvest studies of the Ascophyllum stands are important for understanding recovery, particularly re‐growth of fronds on individual plants and population structure of the resource to inform management. At four sites, we demarcated two control plots and one harvest plot which was mechanically harvested by the local seaweed harvesting team. Biomass and cover of all fucoids and plant height of Ascophyllum plants were measured on shore transects from 2016 to 2021. Ascophyllum harvesting was most efficient in the middle and lower parts of its zone on the shore due to tidal and mechanical constraints of cutters on the upper shore. Efficiency of the harvesting at mid and low shore ranged from 35% to 66% biomass removal at sites where harvesting effort was measured. Ascophyllum reached pre‐harvest cover within 3 years at all sites. Ascophyllum biomass recovered within 5 years at all sites; but pre‐harvest plant height had not been reached within the 5‐year study period. Harvesting efficiency varied among the four sites due to variability in shore topography. Despite the large biomass removed, it was difficult to distinguish between the effect of harvesting and occasional disturbance events such as storms. We confirmed the efficacy of rotation of harvesting on a 5‐year cycle. Sustainable stewardship of Ascophyllum benefits from the complex topography of Icelandic shores leading to refuges from cutting, coupled with rotation among shores.