Distribution and population dynamics of the introduced seaweedGrateloupia turuturu(Halymeniaceae, Rhodophyta) along the Portuguese coast

Abstract

Araújo R., Violante J., Pereira R., Abreu H., Arenas F. and Sousa-Pinto I. 2011. Distribution and population dynamics of the introduced seaweed Grateloupia turuturu (Halymeniaceae, Rhodophyta) along the Portuguese coast. Phycologia 50: 392–402. DOI: 10.2216/10-65.1 Despite the increasing number of coastal areas invaded over the last years by the introduced seaweed Grateloupia turuturu, studies on this species are scarce worldwide, and its invasive capability and future impacts remain unexplored. In the present study, we describe the geographical distribution of the species after a few years of colonization of the Portuguese continental coastline. Additionally, we examine the structure and dynamics of one of the first population of Grateloupia in our shores. Seasonal dynamics of standing biomass, density, size structure and inequality (size variability), together with the presence of fertile fronds were investigated during one year. Grateloupia was recorded in midintertidal pools at 11 of the 36 localities sampled, two of which presenting an elevated abundance of fronds. Fronds were present during the entire year, but their size (length and biomass), density and size inequality varied seasonally reaching highest values at the beginning of the summer. The annual cycle of the population studied included a slow-growth phase in winter, a fast-growth phase during spring-early summer when some density-dependent regulation appeared to occur, as well as a dieback phase at the end of summer. In terms of fertility, abundance of fronds bearing reproductive structures were seasonally variable although carposporophytic and tetrasporophytic fronds were recorded throughout the year. The results of this work highlight some of the biological characteristics of Grateloupia turuturu that may determine its invasive nature and its possible impact on native ecosystems.