Population structure and dynamics of Ascophyllum nodosum were analysed in late summer (August/September) 2012-2019 across ten permanent plots (0.25x0.25 cm) situated in the mid-tidal zone of Kobbefjord. Population biomass was non-destructively estimated each year by measuring the length from the holdfast to the tip of the longest shoot and the circumference 2-3 cm above the holdfast (comprising all basal shoots) for all marked individuals. The fresh weight of each individual was then detemined using a previously derived equation between individual biomass and the corresponding lenght and circumference specific to A. nodosum in Kobbefjord (see Olesen et al. xx). Population density was determined as the number of adult (marked) individuals, the number of unmarked juveniles divided into 2-10 cm long individuals and less than 2 cm individuals in each plot. Minimum estimate of biomass production was calculated by summing the biomass gain from all marked individuals showing an increase in biomass from one year to the next, and omitting losses from those experiencing a reduction in biomass between years. Net population growth rate was estimated ln(Nt/N0) where N0 and Nt are the number of marked individuals at year 0 and year t, respectively. Recruitment rate was estimated as ln(N0+Nnew)-ln(N0), where N0 is the number of marked individual at year 0 and Nnew is the count of new indviduals (>10 cm) observed the following year. Mortality rate was estimated as ln(N0/Nsurv) where N0 is the number of marked individual at year 0 and Nsurv the number suvivining until the following year.
