The importance of organism density and co-occurring organisms in biases associated with molecular studies of marine protist diversity

DNA-based molecular methods such as clone libraries constructed of 18S rRNA amplicons have been increasingly employed in surveys of marine protist communities but are known to have underlying biases, and especially haptophytes are known to be underestimated in eukaryotic clone libraries. Using controlled mixtures of laboratory strains, we show that the recovery of organisms in clone libraries is both influenced by their concentration in the environment as well as bias exerted by certain co-occurring organisms.