Microbial biofilm communities (comprised of bacteria, diatoms, protozoa, and fungi) inhabit the surface of intertidal mudflats and comprise a large proportion of shorebirds’ diets. Given their major role in intertidal food webs, understanding biofilm distribution, quantity, and nutritional value for shorebirds is of vital importance. In California’s San Francisco Bay, the largest tidal wetland restoration project in the western U.S., the South Bay Salt Pond Restoration Project (SBSPRP), will transform 6,110 hectares of former salt ponds to a mosaic of wetland habitat types. One of the project’s key uncertainties is whether the restoration will impact mudflat resources such as biofilm. To address this uncertainty, this study is using a multi-scalar approach (1-meter to regional scale) to model biofilm parameters of quantity and quality using both field spectroscopy and satellite remote sensing to capture measurements of chlorophyll-a (chl-a; indicator of biomass), lipids, total organic carbon (TOC), and glucose. In summer 2019, in situ mudflat and biofilm reflectance spectra were collected concurrently with biofilm parameters using an full-spectrum portable spectroradiometer. The team successfully modeled chl-a using an existing optical model of the chlorophyll absorption coefficient (α) at 673 nanometers (nm) that accounts for background reflectance (Launeau et al., 2018), producing an R2 of 0.54 (n = 16, p = 0.001). Correlations between field spectra and lipids, TOC, and glucose were explored through partial least squares regression (PLS), producing R2 = 0.64, 0.64, and 0.59, respectively (n = 16). Given the heterogeneity of biofilm across the mudflat surface, next steps will be to develop methods to scale biofilm parameter estimates with hyperspectral or multispectral imagery. Results will support managers’ need to measure and visualize habitat quality for shorebirds and understand the influence of restoration activities on biofilm resources.
The absorption coefficient at 673 nm of intertidal biofilm measured with a field spectrometer in San Francisco Bay, California.