## 4 Discussion  
Our experiment demonstrates that marine biofilms are highly resilient to stress and disturbance events but have lower tolerances of them when experiencing both together. Productivity was not altered within our experimental timeline, but resultant stoichiometric shifts may lead to less productive biofilms over a longer timescale, affecting local food sources and biogeochemical cycling. Although past studies have focused on how biofilm metabolic activity and structure change after exposure to biosurfactants and grazers separately, no research has been performed to investigate these combined relationships. Prior research has shown that biofilm exposure to synthetic surfactants can decrease respiratory activity temporarily, with full recovery occurring after 12 h [40]. Conversely, antibiotic exposure temporarily increased respiration for several hours for affected single-species biofilms [41]. Biomass has similarly been negatively affected by surfactant exposure over a short time period. Rhamolipid exposure reduced single-species biofilms by 74-98% over a 4-day exposure of a 4-day-old biofilm [42]. Grazing on biofilms from known biofilm feeders has also been seen previously to significantly decrease biofilm biomass after a period of 3-4 days [43]. Our study took place over a longer time period than the previous studies, and the exposure started before the initial growth occurred. Therefore, it is likely that the lack of significant differences in GPP, CR, and biomass occurred due to the longer experimental timeline allowing the biofilm time to recover and adapt its growth to the presence of a surfactant stressor. Our GPP and CR results are also comparable to other studies examining the GPP and CR of biofilms overall, demonstrating a similar productivity level to other aquatic biofilms [44; 45]. In addition, our results were comparable to another long-term study, where a 32-day exposure of rhamnpid yielded no differences in examined GPP, CR, or biomass for exposed freshwater biofilms, where exposure to the surfactant also occurred before biofilm development began [46]. As originally hypothesized, exposed biofilms demonstrated strong tolerance and resistance to grazing effects. Our results also indicate the development of a potentially holobiontic relationship, as biomass increased and productivity remained high and similar to the control per cm\({}^{2}\) of biofilm material examined. The formation of a beneficial relationship between biofilms and grazers in our study is supported by previous studies where similar results occurred, although we obtained our evidence over a much smaller timeframe. Limpet grazing of epilithic biofilms over the summer when growth and grazing  
Figure 3: Carbon (**A**) and nitrogen (**B**) quantities within marine microbial biofilms (\(n\) = 8) exposed to either predation by the common periwinkle snail and/or 150 ppm rhamnpid. Dots indicate outliers in the data for figure visualization. All mesocosms were treated similarly and were thus equally affected by the low-level deposition of inorganic solids from the sea water flowing through the system. This deposition decreased the relative carbon and nitrogen contents within the measured biofilm, which were analyzed after a 14-day exposure. rates peaked led to biofilm biomass growth increases of 20% later on in the season [47]. Nutrients from grazer excretion can also specifically increase microhydrobethnic growth, which would then affect local biofilm productivity [48]. Nutrients obtained from grazer excretion are typically P [49] and N [50], which would explain why biofilms exposed to only grazers within our mesocosoms had altered stoichiometry with decreased C:N ratios and increased N. Relatively low C and N contents in percent of biofilm dry mass were attributable to the inevitable low-level deposition of inorganic solids from the water flowing through the system.