Testing top-down vs bottom-up influences on marine biofilm communities

Microbiomes have become central in understanding marine ecosystems. While describing the community composition has become easy, determining drivers of microbial community structure still lacks a solid framework. Ecological theory predicts two fundamental categories for community drivers: bottom-up or top-down control. For microbial ecology the focus has been on bottom-up control which assumes communities are structured by abiotic factors limiting growth [e.g. availability of macro and micronutrients, or preference of habitat type]. However, top-down control through biotic interactions [i.e. competition or predation] has received less attention. Microbial studies are frequently limited to identifying drivers of community structure associated only to bottom-up controls, likely due to the ease of assessing physicochemical drivers. This ignores the potentially crucial role that top-down controls play in microbial ecology through preferential predation of microbes. Here we present results from a study that assesses the degree of influence of top-down and bottom-up controls on a marine biofilm. Through predator exclusion experiments [limiting access to biofilms to only organisms <100 µm] and utilization of multiple substrates for establishment of biofilms we quantified the contribution of both top-down and bottom-up controls to shaping microbial communities using 16s and 18S amplicon sequencing.