Can the reproductive traits of Asparagopsis taxiformis contribute to its success as an invader? We present the reproductive phenology of a population located in southern Spain and a quantitative study of gametophyte reproductive structures. Reproductive allocation (the proportion of biomass allocated to reproductive tissue) in different size classes was analysed to investigate whether the shoot size influences the reproductive output of this population. Gametophytes were found to be reproductive in spring, autumn and the beginning of winter, whereas fertile tetrasporophytes were never observed. High reproductive performance was recorded in July, when reproductive allocation was surprisingly low (12.74±4.79%). Reproductive allocation of each size class varied over the study period, ensuring a continuous reproductive yield. The shoot size for reproduction ranged between 4–6 cm and 24–26 cm. An analysis of reproductive and vegetative volume suggested that reproductive allocation decreases with shoot size, which, as intermediate size classes are the most abundant and most persistent in the field throughout the year, optimizes the reproductive output. Reproduction in gametophytes was independent of environmental conditions in the study area. The yearly persistence of gametophytes together with the abundance of tetrasporophytes makes this population a donor source for future invasive populations.
