Vegetative and reproductive phenology of Zonaria tournefortii (Dictyotales, Phaeophyceae) in sublittoral populations off the Canary Islands

Abstract

Sublittoral populations of Zonaria tournefortii off the Canary Islands were studied to monitor vegetative and reproductive phenology. Sterile individuals, sporophytes and gametophytes coexisted throughout the year, but significant differences were detected between seasons and life-history stages for most parameters tested. Density was maximal in autumn (3513 individuals m-2). Twenty-five percent of all individuals were fertile, with sporophytes at much higher densities than gametophytes in all seasons. The highest average individual thallus length occurred in winter, but the highest frequencies of long specimens and the greatest size inequalities were in summer. Fertile thalli were significantly longer than sterile thalli, however, sporophytes and gametophytes had similar average lengths. Populations exceeded 100% overall cover in all seasons (up to 552% in autumn), with highest cover occupied by fertile individuals. Overall biomass, produced mainly by sporophytes, was maximal in summer-autumn (981 g DW m-2). Results suggest that this perennial species exhibits a somewhat exceptional phenological pattern amongst dictyotaleans. Its phenology was regulated in most years by elevated water turbulence in early winter, which causes breakage or loss of whole individuals. Blade regeneration and recruitment from the remaining damaged individuals began in winter-spring, and continued until autumn. Individual growth, hierarchical structuring and maturation of populations occurred mainly in spring-summer. Optimal reproductive potential per individual occurred during summer, although the reproductive potential per unit area was similar among seasons.