Recruitment patterns in the Mediterranean deep-water alga Cystoseira zosteroides

Although recruitment is considered an essential process regulating populations of many marine species, there is still a lack of knowledge about the ultimate factors that influence it. This is especially true for seaweeds, where population dynamics studies are also lacking. The main objective of this study was to investigate the main mechanisms driving the recruitment patterns of an emblematic deep-water alga in the NW Mediterranean, Cystoseira zosteroides, and its influence on their population dynamics. Five C. zosteroides populations were monitored annually at different sites along the coast of Spain by using permanent transects over 3-4 years. Some of these populations suffered mass mortality events from natural or anthropogenic disturbances, allowing us to study the influence of such events. Our findings agreed with the expected results for a long-lived species. Under low frequency of disturbances, C. zosteroides populations displayed few fluctuations over time given the longevity of the adults, and they were poorly influenced by the dynamics of early life stages because of negative density-dependent control of conspecifics. Moreover, disturbances had a great influence on population dynamics because the removal of adults decreased the effects of density-dependent processes and enhanced the recruitment. Nonetheless, a high mortality was found for early life stages (similar to 50 % year(-1)), contrasting with the high survival of adults (similar to 90 % year(-1)). This study confirmed the slow population dynamics of these deep assemblages, demonstrated the influence of density in the C. zosteroides population dynamics and highlighted their vulnerability to the increase in natural and human-induced disturbances.