## 1 Introduction  
Microorganisms, such as those making up microbial biofilms, are major drivers of biogeochemical cycling (or nutrient movement across abiotic and biotic elements) within aquatic ecosystems [1; 2; 3; 4]. In marine environments, these biofilms are often made up of bacteria, which are important cycles of dissolved organic matter [5; 6], and diatoms, depending on their location [7]. Diatoms can break down and recycle environmental nutrients, such as nitrogen, which is necessary in typically nitrogen-limited marine environments [8; 9]. Diatoms are also very important autotrophs, acting as major primary producers in marine environments [10; 11]. Living within biofilms is a way that microorganisms can protect themselves against outside biotic and abiotic stressors and disturbance events, including environmental changes or contaminant exposure [12]. The surrounding extracellular polymeric substance (EPS) matrix, formed by microorganisms within the biofilm [13], limits compounds, such as antibiotics, from reaching the bacterial cells and other microorganisms within the biofilm [14; 15; 16]. This matrix has a high carbon content and is mainly composed of compounds such as proteins, lipids, polysaccharides, and extracellular DNA [17]. The structure of the EPS matrix itself also provides biofilms a measure of protection against predation and grazing. For example, cellulose in the EPS matrix gives biofilms resistance against the mechanical forces of predation from _Caenorhabditis elegans_ (nematode) [18]. Biofilms have complex relationships with other aquatic organisms. For many, such as predatory bacteria [19], nematodes [20], invertebrates, and various fish taxa [21], the biofilms are an important food source. However, they also have holobiontic (where a symbiotic relationship forms between hosts and the surrounding microbiats, creating a unique ecosystem [22]) and mutualistic relationships with other marine organisms. Holobionic relationships have been noted among grazers where snails [23] and limpets [24] remove unproductive canopy from the biofilm. This encourages new biofilm growth and greater productivity, leading to benefits to both the grazer, which also acts as the host for microorganisms, and the surrounding biofilm itself. Research has shown that the presence of filter feeders, such as mussels and tadpoles, in aquatic environments can increase benthic primary production and increase nitrogen (N): phosphorus (P) ratios within aquatic biofilms, leading to a bottom-up effect on the food chain from consumers [25; 26]. These beneficial relationships are important for local biofilm and grazer health, and any alterations in biofilm stoichiometry (determined through testing carbon (C) and N within the biofilm that indicate changes in the EPS matrix and nutrient levels) potentially indicate shifts in biofilm productivity and composition. Although organisms such as snails can positively influence biofilm and EPS accumulation, microorganisms within a biofilm typically produce biological surfactants, such as rhamnols, as a way to control their EPS matrix size and structure [27; 28]. Surfactants are part of a chemical class that reduces surface tension through micelle formation. Micelles occur when molecules form an aggregate where hydrophobic tails or chains are on the inside [29] and the hydrophilic moieties (or heads) of the amphiphilic compound are on the outside [30]. Biological surfactants, such as rhamnols, are currently being investigated for their ability to control biofilm growth industrially and medically in a more environmentally friendly way than synthetic alternatives, which have a known toxicity within the environment [31]. With a growing presence of anthropogenic chemicals within marine environments [32], marine biotas are constantly exposed to low levels of these pollutants. Surfactants specifically are being introduced in great diversity and quantity to the marine environment due to their heavy use in cargo ships, oil cleanups, and ocean drilling [32].