Fragment production and recruitment ecology of the red alga Laurencia poiteaui in Florida Bay, USA

In 2000 and 2001, Laurencia poiteaui (Rhodophyta, Ceramiales) was the dominant organism in the patchy seagrass beds off Long Key in Florida Bay. Earlier research established that asexual fragmentation is the predominant mode of reproduction in this benthic drift macroalga, yet no studies documenting post-fragment success have been published to date. To better understand fragmentation, and ultimately recruitment of L. poiteaui, we examined fragment: 1) accumulation rates, 2) variability, 3) dispersal distances, and 4) attachment rates. In July 2000 and July 2001, the majority (>50%) of the algal fragment pool near Long Key was comprised of L. poiteaui. The length of these fragments ranged from 0.7 to 15.7cm, but >75% of the collected fragments were <6cm. Short dispersal distances (<7cm within beds of the seagrass Thalassia testudinum and<30cm over sand after 7days) and fast attachment rates (<48h) suggest that most fragments (3–4fragments/day/m2) recruit locally. Attachment success of L. poiteaui fragments was high in both laboratory and field (95.5% and 88.2%, respectively). Sand and silt decreased the attachment rate of L. poiteaui, but the presence of a terminal apical tip had no influence. The combination of high fragment production, slow dispersal rates, and rapid attachment rates of L. poiteaui ultimately suggests that vegetative fragmentation plays an important role in the abundance of this macroalga in the calm, shallow areas of southeastern Florida Bay.