Botanica Marina 49 (2006): 406–416  2006 by Walter de Gruyter • Berlin • New York. DOI 10.1515/BOT.2006.052 Article in press - uncorrected proof 2006/42 Vegetative and reproductive phenology of Zonaria tournefortii (Dictyotales, Phaeophyceae) in sublittoral populations off the Canary Islands Marı´a A ´ ngeles Montan ˜e ´ s, Marta Sanso ´ n* and Javier Reyes Departamento de Biologı ´a Vegetal (Bota ´ nica), Universidad de La Laguna, 38271 La Laguna, Islas Canarias, Spain, e-mail: msanson@ull.es * Corresponding author 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. Den- sity was maximal in autumn (3513 individuals m -2 ). Twen- ty-five percent of all individuals were fertile, with sporophytes at much higher densities than gameto- phytes in all seasons. The highest average individual thallus length occurred in winter, but the highest fre- quencies of long specimens and the greatest size in- equalities 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 indi- viduals. Overall biomass, produced mainly by sporo- phytes, 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 caus- es breakage or loss of whole individuals. Blade regen- eration 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. Keywords: Canary Islands; phenology; reproductive potential; seasonal variations; Zonaria tournefortii. Introduction The brown algal genus Zonaria C. Agardh currently includes ten species (Guiry and Nic Dhonncha 2006). It has a broad global distribution in temperate waters, especially in the Australasian region (Phillips and Nelson 1998). On Atlantic coasts, Zonaria is represented only by the type species, Z. tournefortii (Lamouroux) Montagne, which has been reported also from the Mediterranean Sea and the eastern coasts of South Africa (Schneider and Searles 1991, Montan ˜e ´ s et al. 2002). As in all Dictyotales, Zonaria tournefortii has a life-his- tory with two isomorphic free-living generations, diploid sporophytes and haploid dioecious gametophytes, which can be distinguished only by their mature reproductive structures (Sauvageau 1905, Schneider and Searles 1991, Montan ˜e ´ s et al. 2002). Thalli are characterized by an erect habit, up to 30 cm long, with abundant terminal flabellate blades, branched cylindrical stipes of rhizoidal origin, and a basal discoid holdfast (Montan ˜e ´s et al. 2002). Zonaria tournefortii has been documented as an epili- thic sciaphilous species, growing commonly from lower- eulittoral rockpools to 30 m depth (Neto et al. 2000). Off the Canary Islands, it is also the dominant macrophyte in some dense submarine communities and is a member of deep-water assemblages at more than 90 m depth (Børgesen 1938, Montan ˜e ´ s et al. 2002). The vegetative and reproductive phenology of this widely distributed species are still little known, in contrast to the other spe- cies of Zonaria with more restricted distributions (King and Farrant 1987, Phillips et al. 1994, Phillips and Clay- ton 1997, Phillips and Nelson 1998). Peckol (1982) reported the seasonal occurrence and reproduction of Zonaria tournefortii in North Carolina, USA, however there is a lack of detailed phenological data for the east- ern Atlantic coasts. The aim of this study was to analyse the seasonal patterns in abundance and reproduction of the species in shallow sublittoral populations. We gave emphasis to changes in density, morphology and bio- mass of life-history stages. Studies were also carried out to estimate the reproductive potential of Z. tournefortii through the year. This information is not available for any dictyotalean species. Materials and methods The study site was Playa de San Marcos, a semi- exposed bay on the north coast of Tenerife, Canary Islands (28821’N, 16842’W) (Figure 1). The sublittoral zone comprised 70% rocky bottom and 30% sand. Popula- tions of Zonaria tournefortii were the most extensive sea- weed beds, forming dense meadows covering about 1.2 ha of rocky substrata, from 3 to 15 m depth (Mon- tan ˜e ´ s et al. 2002). Samples were taken on the west side of the bay by SCUBA diving (Figure 1). Samples were collected sea- sonally in October 1997 (autumn), February (winter), May Brought to you by | University of Arizona Library Authenticated | 150.135.135.70 Download Date | 11/21/12 12:07 PM