Epidermal shedding in Ascophyllum nodosum (Phaeophyceae): seasonality, productivity and relationship to harvesting

Epidermal shedding, a process that effectively controls epiphyte accumulation on certain long-lived macroalgae, was quantified weekly for over 1 year in a population of Ascophyllum nodosum from Nova Scotia. About 25% of the frond epidermis is shed per week and for at least 9 months of the year, this shedding occurred in population-level cycles of skin shedding followed by reaccumulation of epiphytes. Using a geometric model based on cross-sectional area of branches assigned to one of four size categories, we determined that about 1% of frond biomass is shed during each monthly cycle. Taking into account the differences in frond architecture at 10 sites from around Nova Scotia, an estimated 10% of vegetative frond biomass enters coastal waters each year solely as a result of epidermal shedding. This natural contribution to coastal detritus amounts to about 2 t ha(-1) of Ascophyllum beds in Lobster Bay, the primary harvest region for Ascophyllum in Nova Scotia. This is a significant and previously unconsidered addition to the environmental impact of the annual harvest of over 20 t ha(-1) that is reported by industry from this area. These data form part of a wider assessment of the impact of the commercial harvest of Ascophyllum on biomass removal from coastal detrital food webs.