Ascophyllum nodosum - population structure and dynamics

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.2012至2019年夏末（8月/9月），我们对科布峡湾（Kobbefjord）潮间带中区的10个永久性样地（0.25×0.25 cm）内的泡叶藻（Ascophyllum nodosum）种群结构与动态开展了分析。每年均通过测定所有标记个体从固着器（holdfast）至最长茎（shoot）尖的长度，以及固着器上方2~3 cm处（包含所有基生茎（basal shoots））的周长，对种群生物量进行非破坏性估算。随后利用先前推导得到的、针对科布峡湾泡叶藻的个体生物量与对应长度、周长间的关系式，计算得到每个个体的鲜重（fresh weight）（详见Olesen等xx）。种群密度通过以下方式计算：样地内成年（标记）个体数量，以及划分为2~10 cm长度组与小于2 cm长度组的未标记幼体（juvenile）数量之和。生物量生产（biomass production）的最小估算值通过累加所有标记个体在年度间的生物量增量得到，同时剔除年度间生物量下降个体对应的损失量。种群净增长率（net population growth rate）通过ln(Nt/N0)估算，其中N0与Nt分别为第0年与第t年的标记个体数量。补充率（recruitment rate）通过ln(N0+Nnew)-ln(N0)估算，其中N0为第0年的标记个体数量，Nnew为次年观测到的新个体（长度>10 cm）数量。死亡率（mortality rate）通过ln(N0/Nsurv)估算，其中N0为第0年的标记个体数量，Nsurv为存活至次年的个体数量。