Spatio-temporal variations and recruitment of Sargassum flavifolium Kützing in sublittoral cobble bottoms: relationships with environmental variables

Abstract

Dynamics of Sargassum flavifolium Kützing were studied in sublittoral cobble bottoms. The analyses showed that some morphological attributes (thallus length and number of branches, blades, stipes and receptacles) were related to selected environmental variables (depth, cobble size, temperature, wave exposure and day length), and spatio-temporal differences in selected variables (thallus length, reproductive capability, recruitment and number of thalli per cobble) were found. S. flavifolium showed an annual life cycle with marked variations in habit along the year and between locations. The longest thalli were found in May–July coinciding with annual increases in seawater temperature and day length, and the decrease in wave exposure. However, depth and cobble size were also variables that interacted with this seasonal pattern, and as a result, differences in Sargassum development could be observed within a site or at the same depth. The longest thalli were found at the deepest bottoms and on larger cobbles. The highest number of receptacles occurred on the largest individuals, and the greatest percentage of fertile thalli was observed in the deeper samples. Reproduction and recruitment were coupled, and recruits were conspicuous and more numerous in shallow cobbles. Significant differences in number of thalli per cobble were observed between months, although changes related to recruitment were only observed in small cobbles.