CHARACTERISTICS AND FORMATION DRIVERS OF INTERTIDAL BIOFILMS AT AN OPEN OCEAN-FACING SANDY BEACH

Intertidal biofilms on sandy sediments are commonly observed on sand flats and relatively quiescent embayments, but rarely on open ocean-facing beaches. Visually prominent colored patches are routinely observed in the sandy-beach intertidal zone of Waties Island, South Carolina, a privately-owned island with restricted human access. The biofilms transform along spatial and temporal scales: their intensity changes with time of day and time of year, while their position on the beach shifts with the presence of runnels and stage in the lunar tidal cycle. Such biofilms have not been observed elsewhere in the Grand Strand, where many beaches are extensively frequented by locals and visitors alike and are often mechanically groomed. Chlorophyll concentrations are very high in these biofilms which, consequently, may be an important site of primary productivity and key in supporting the intertidal infaunal food. This study builds on our current understanding of the spatiotemporal scales of biofilm development and focuses on their chemical characterization. Specifically, biofilm-associated pore-water and solid-phase nitrogen, phosphorus and iron will be analyzed across the tidal cycle to test for the influence of pore water or ground water emersion as a key driver for biofilm formation and persistence. Understanding the geochemical character and formation drivers of intertidal biofilms may inform our understanding of intertidal productivity and food webs and consequences for beach management practices.