Effects of competition and dispersal on the recruitment of the annual kelp Nereocystis luetkeana

Abstract

In central California, the role of algal assemblages on the recruitment of the canopy producing annual kelp Nereocystis luetkeana was examined by experimentally manipulating canopy and understory algae within 1) a Macrocysits bed and 2) a Nereocystis bed. Nereocystis reproductive material was introduced in some plots to examine the role of dispersal distance on recruitment. Nereocystis recruitment at both sites was significantly higher during spring compared to recruitment observed later in the study. Recruitment continued throughout the fall, however, suggesting a broad recruitment window. Recruitment success increased dramatically when understory algae were removed. Presence of a canopy (Nereocystis or Macrocystis) did not affect Nereocystis recruitment, suggesting that Nereocystis was not directly competitively inferior to Macrocystis. Greater recruitment was observed in areas seeded with Nereocystis propagules. Ultimately, recruitment of Nereocystis was controlled by understory algal assemblages and by the relatively short dispersal distance of its propagules. Additionally, the broad recruitment window for Nereocystis described here suggests that summer recruits can contribute to population resilience to late spring disturbances. This study indicates that given sufficient disturbance to the benthos and ample propagule supply, Nereocystis should be able to recruit and colonize new areas, regardless of the presence of Macrocystis.