Phenology, biomass and productivity of sub-Antarctic Ruppia filifolia

Abstract

Seagrasses play important ecological roles in shallow coastal ecosystems from tropical to sub-polar seas. Ruppia filifolia (Phil.) Skottsberg is the seagrass with the world's southernmost distribution but with virtually unknown biology and ecology. The goal of this study was to identify the ecological roles that R. filifolia might play in sub-Antarctic environments through the assessment of the development and primary productivity of this aquatic flowering plant. We monitored biomass and shoot density, rhizome growth and the presence of reproductive structures during 1 year in Skyring Sound, sub-Antarctic Chile. Ruppia filifolia forms perennial meadows with high biomass (124-293 g DW m(-2)) and shoot density (1800-5300 shoot m(-2)), a continuous presence of vertical stems and a rhizome plus root to shoot biomass ratio > 1. Plant development shows a unimodal seasonal pattern with flowering in spring, and fruiting and maximum growth during summer. An average rhizome plastochrone of 37 days and median rhizome elongation of 27.5 cm plant(-1) year(-1) rank R. filifolia as a slow-growing seagrass. Primary productivity varied from 0.5 to 4.2 g DW m(-2) day(-1), resulting in an annual primary production of 700 g DW m(-2). Ruppia filifolia in sub-Antarctic environments might play ecosystem roles (carbon sequestration, sediment stabilization, structural habitat, nutrition sources) as important as those played by seagrasses in tropical or temperate coastal environments.