LAUSR

Abstract Primary production of a population of the red invasive seaweed A. taxiformis from southern Spain was assessed using a demography-based approach and studied in relation to environmental conditions. In-depth analysis of shoots biomass of different size classes revealed a population dynamic characterized by six cyclic cohorts that followed consecutively or overlapped along the study period. Cohorts differed in their longevity, resource exploitation and contribution to the whole population’s primary production. Altogether, annual primary production of the population was 253.17 g DW m−2. The most productive one was cohort III, which was also the briefest (26 days) and occurred at the beginning of autumn. Cohort III allocated its productivity towards the synthesis of the fixation structure, the increase of shoots size and reproduction. The development of cohorts I and VI was favoured by high irradiance, increasing temperatures and daylight hours, while cohorts III, IV and V were dependent on nutrient availability. Maximum expansion of this species matches with spring peak of oxidized nutrients (nitrate, nitrite and phosphate), but it is also able to produce new cohorts in summer and winter periods, when reduced nutrients (ammonium) are predominant. Principal Component Analysis revealed that primary production of the studied population was not related to environmental variables considered. Nevertheless, the presence of different cohorts in A. taxiformis that respond singularly to a changing environment allows this species to maintain a constant production, what can reinforce its invasive behaviour in the area.