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\section{Discussion}   \subsection{Biomass Pool Size} The goal of this study was to evaluate how changes in available C affected the biomass pool size,  membership size  and structure composition  of planktonic and biofilm communities. Our results suggest that C subsidies increased heterotroph biomass in both plankton and biofilm communities as predicted. communities.  C amendments also resulted in decreased photoautotroph biomass in the plankton community, but there was no significant change in biofilm photoautotroph biomass between resource treatments. Although the DOC concentration in the highest C treatment was significantly higher than the other treatments, the concentrations we measured were in the range of those reported in natural marine ecosystems \citep{Mopper1980} and it is has been noted that glucose concentrations in coastal marine ecosystems may fluctuate over several orders of magnitude \citep{Alonso2006}. The changes in the biomass pool size that did occur were consistent with changing relationships (commensal to competitive) between the autotrophic and heterotrophic components of the plankton communities but not necessarily of the biofilm communities. While we recognize that other mechanisms may drive the shift in biomass pool size of these two components of the microbial community (e.g. increased grazing pressure on the algae with C additions, or production of secondary metabolites by the bacteria that inhibit algal growth) previous studies \cite{Stets_2008,Cotner_2002} and the data reported here suggest that altered nutrient competition among heterotrophic and photoautotrophic members of the plankton is the most parsimonious explanation for this shift in biomass pool size. \subsection{Biofilm and Plankton Alpha and Beta Diversity} Beyond changes  in the biomass pool size of each community, we explored how shifts in  resource C affecteda)  the membership and structure of each community, andb)  the recruitment of plankton during biofilm community assembly. Intuitively, shifts in planktonic community composition should alter the  available pool of microorganisms that can be recruited into a biofilm. For  example, if planktonic diversity increases, the number of potential  
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represent a temporally integrated sample of the planktonic organisms moving  through the reactor resulting in higher apparent alpha diversity (i.e. mass  effects would be the dominant assembly mechanism). Second, the biofilm  environment may disproportionately enrichfor  the least abundant low abundance  members of the planktonic community. In this case it is probable that the biofilm would  incorporate the most abundant members from the planktonic community (i.e. mass  effects) but also select and enrich (i.e. species sorting) the least abundant 
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populations when compared to the most abundant members of the plankton  community. As noted above, in the highest C treatment (C:P = 500) the  heterotroph biofilm and plankton community membership had significant overlap  at the final timepoint (Figure~\ref{fig:pcoa}). However, heterotrophic plankton membership community composition  for the highest C treatment among timepoints (8 and 17 days) were also qualitatively as similar to each other as any other  community. Thus, variable planktonic community composition among timepoints  would not explain the higher diversity observed in the biofilm compared to the 
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treatment levels and both timepoints. While we did not (could not) specifically  measure niche diversity within the biofilm communities our results suggest that  the biofilm habitat selected for unique members of the photoautotroph and  heterotrophic community that were in low abundance in the planktonic habitat but readily became major constituents of the biofilm community. % Fakesubsubsection:few studies have  Few studies have simultaneously evaluated the relationship among membership 
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intermediate peak in OTU richness is consistent with a classic  productivity-diversity relationship that has been shown for many ecosystems and  communities both microbial and otherwise. However, as with other experiments  with this result our experimental design did not allow us to tell whether resources drove productivity that subsequently  drove changes in diversity or whether resources drove diversity which altered productivity. Rather, we note that as diversity decreased in the highest C treatment, heterotrophic plankton and biofilm membership became increasingly similar. This suggests that environments that contained high amounts of labile C selected for fewer dominant taxa, overwhelming the lifestyle species sorting mechanisms that appeared to dominate biofilm community assembly in all other treatments. Similarly, while we did not measure extracellular polymeric substances (EPS), direct microscopy showed that planktonic cells in the highest C treatment (C:P = 500) were surrounded by what appeared to be EPS. Because biofilm EPS appeared also to increase moving from the low to high C treatments it is possible that more abundant planktonic cells were more readily incorporated into biofilms due both to increased "stickiness" of the planktonic cells as well as the biofilm itself. While we did not observe flocculating DOC which has been shown to dominate high DOC environments in nature, we did measure a substantial increase in DOC in the C:P = 500 treatment which was more than 2-fold higher than any of the other treatments. Thus additional adhesion of the plankton and the biofilm may also explain the merging of the planktonic and biofilm heterotroph membership in the highest C treatment. \subsection{Lifestyle (biofilm or planktonic) Enriched OTUs} There are only a  few studies that attempt to compare biofilm community composition and the 
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the plankton) but are readily enriched in the biofilm lifestyle. Most of the  biofilm enriched photoautotroph OTUs were \textit{Bacillariophyta} although  there were also many \textit{Bacillariophya} OTUs enriched in the planktonic  libraries. We also found more  \textit{Cryptophyta} and \textit{Viridiplantae} weremore uniformly  enriched in the planktonic photoautotroph libraries. It appears that these broad taxonomic groups were selected against in biofilms under our experimental conditions. Heterotroph OTUs enriched in planktonic samples  displayed more dramatic differential abundance patterns than heterotroph OTUs  enriched in biofilm samples, but, biofilm enriched heterotroph OTUs were spread 
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in the highest C treatment. Consistent with a growing body of work our results  suggest that complex environmental biofilms are a unique microbial community  that form from taxa that are found in low abundance in the neighboring  communities. This membership was affected by C amendments for heterotrophic but not autotrophic photoautotrophic  microbes and then only in the most extreme resource environment. This suggests that lifestyle is a major division among environmental microorganisms and although biofilm forming microbes must travel  in planktonic form at some point, reproductive success and metabolic  contributions to biogeochemical processes comes from those taxa primarily if