Bryan L Morse1, Jean-Sébastien Lauzon-Guay1 and Raúl A. Ugarte1
1Acadian Seaplants Limited, 30 Brown Ave, Dartmouth, Nova Scotia, B3B 1X8, Canada
The recruitment of new individuals into an existing bed of Ascophyllum nodosum is required for population maintenance after disturbances such as storms or ice scour. However, it is known that the spatial distribution of new recruits is not uniform. While small timescale studies have highlighted the importance of individual post-settlement factors on the loss of recently settled zygotes, few large-scale surveys of recruits have been completed. We measured the recruitment of A. nodosum in Eastern Canada in the field, alongside wave exposure, predation pressure, tidal height, and substrate type. Abundance of A. nodosum recruits decreased with the abundance of their main herbivorous snail. This was observed both within beds, and between larger regions which also differed in substrate type. To tease apart the effect of snail abundance and substrate type on recruitment, a common garden experiment was set-up in two locations. One site was in southwest New Brunswick where the dominant bedrock is a basalt with a complex surface, the other site was in southwest Nova Scotia where the dominant bedrock is a granite with a more uniform surface. After three years, our results indicate that a complex substrate type facilitates recruitment. Deep cracks are thought to provide protection from both wave action and predation during the post-settlement period. Our findings indicate that there are a number of physical and biological factors that drive the successful recruitment of A. nodosum in Eastern Canada and suggests that the timescale of population recovery after disturbance could differ greatly between regions.