Life history traits of Laminaria ochroleuca in Portugal: The range-center of its geographical distribution

While the life cycle and conditions affecting most species in the genus Laminaria are quite thoroughly studied, little is known about Laminaria ochroleuca, the main forest forming perennial kelp species of Southern Europe. Growth, recruitment, and reproduction of L. ochroleuca were recorded in the field on a monthly basis during one year, in 2013, while sporulation induction experiments were performed in the laboratory to study reproduction triggers, in 2013 and 2014. In the field, L. ochroleuca individuals were followed at 4 different locations and divided into two stages: recruits, too small to become reproductive, and adults. Recruitment was observable year round, except for winter (January and December), peaking in early summer (around June), and preceding peak reproduction by about two months. Reproduction occurred from mid spring to early winter (April to December), peaking in late summer (August-September). Maximum relative elongation rate (RER) occurred between late winter and early summer (from February to June) for adults and between late winter and late summer (from February to August) for recruits. The two stages followed a similar pattern, with recruits occasionally elongating significantly faster. RER was similar for non-reproductive individuals and those undergoing sporogenesis, which disagrees with an inhibitory effect of meristem activity on sporogenesis reported for other kelp species. Laboratory sporogenesis trials confirmed these observations and further showed that sori developed independently of blocking the transport of the putative sporogenesis inhibitor released by the active meristem. Further studies are needed to better understand the mechanisms controlling sporogenesis in this species.