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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 producitons 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 is the most parsimonious explanation for this 

mesocosm (C:P = 500) include OTUs in classic copiotroph families such as  \textit{Altermonodales} and \textit{Pseudomonadaceae}. Interestingly, the most  depleted OTU in the high C treatments is annotated as being in the HTCC2188  order of the \textit{Gammaproteobacteria} and shares 99\% sequence identity with another "HTCC" strain (accession AY386332). HTCC stands for 'high throughput culture collection' and is a prefix for strains cultured under low nutrient conditions \citep{Cho_2004, Connon_2002}.  \subsection{Conclusion} In summary this study shows that changes in low resolution community level dynamics are concurrent with changes in the underlying constituent populations that compose them. We found that autotrophic pools and heterotrophic pools         

\section{Materials and Methods}  \subsubsection{Experimental Design}  We placed test tube racks in one smaller (185L, control) and 3 larger (370L)  flow-through mesocosms. All mesocosms were fed directly with marine water from an inflow source in Great Bay approximately 200 m from the shore. Each mesocosm had an adjustable flow rate that resulted in a residence time of approximately 12h. Irregular variation in inflow rate meant that flow rate varied around that target throughout the day, however, regular monitoring ensured that the entire volume of each system was flushed approximately two times per day. To provide a surface for biofilm formation we attached coverslips to glass slides using nail polish and then attached each slide to the test tube racks using office-style binder clips. Twice daily 10 ml of 37 mM KPO$_{4}$ and 1, 5 and 50 ml of 3.7M glucose were added to each of 3 mesocosms to achieve target C:P resource amendments of 10, 100 and 500 respectively. The goal of the resource ammendements amendments  were to create a gradient of labile carbon among treatments. The same amount of P was added to each treated mesocosom mesocosm  to ensure that response to additions of C were not inhibited by extreme P limitation. The control mesocosm did not receive any C or P amendments. \subsubsection{DOC and Chlorophyll Measurements}  To assess the efficacy of the C additions we sampled each mesocosm twice 

bacterial abundance. Once it was clear that pool size of each community had  been altered (day 8) we filtered plankton onto 0.2 $\mu$m filters and harvested  coverslips to assess bacterial and algal biofilm community composition (16S and 23S  rDNA). In addition all mesoscosms mesocosms  were analyzed for community composition a second time (day 17) to assess how community composition of both the plankton  and biofilm communities had been altered over time. Control samples were only  analyzed for community composition on day 17.