The ecology of microbial communities associated with Macrocystis pyrifera

Kelp forests are characterized by high biodiversity and productivity, and the cycling of kelp-produced carbon is a vital process in this ecosystem (Mann 1982; Mann 2000). Although bacteria are assumed to play a major role in kelp forest carbon cycling, knowledge of the composition and diversity of these bacterial communities is lacking. Bacterial biofilms on the surface of Macrocystis pyrifera were sampled at the Hopkins Marine Life Refuge in Monterey Bay, CA, before and after the onset of spring upwelling. The population distribution of the biofilm and adjacent seawater bacterial communities were studied using 454-tag pyrosequencing (16S RNA). Our results suggest that M. pyrifera harbors species-specific microbial biofilms that respond to changes in the environment. We identified several kelp-specific taxa that were highly similar to other bacteria known to either prevent the colonization of eukaryotic larvae or to exhibit antibacterial activities. We also identified host-specific bacterial associations that might play an important role for M. pyrifera. This study reports on the first in-depth assessment of the diversity and phylogenetic profile of the bacterial communities associated with M. pyrifera.