Dynamic satellite seascapes as biogeographic framework for tracking seasonal shifts of phytoplankton assemblages in south Florida waters

Physical, chemical, geological, and biological factors interact in marine environments to shape complex but recurrent ecological organization patterns on multiple spatial and temporal scales known as seascapes. We sought to characterize such biogeographic seascapes for the Florida Keys National Marine Sanctuary (FKNMS; 24.3-25.7° N, 80.1-83.2° W) using multivariate satellite and in situ measurements of Essential Ocean Variables. Dynamic seascapes were derived by combining satellite time series of sea surface temperature, chlorophyll-a concentration, and normalized fluorescent line height (nFLH) using a supervised thematic classification for three periods during which oceanographic expeditions were conducted (March 11-18, May 9-13, and September 12-19, 2016). In situ observations collected during these periods included bio-optical parameters (particulate and dissolved spectral absorption coefficients), phytoplankton community composition, and hydrography. Phytoplankton community composition was evaluated using 1) chemotaxonomic analysis (CHEMTAX) based on high-performance liquid chromatography (HPLC) pigment measurements, and 2) analysis of spectral phytoplankton absorption coefficients (a_phy). The seascapes represented areas of different salinity and nutrients within which different phytoplankton communities were present, as determined by hierarchical cluster analyses of HPLC pigments and a_phy spectra. Oligotrophic, Mesotrophic and Transition seascape classes of deep, offshore waters were dominated by small phytoplankton (< 2 mm; ~ 40-60 % of total cell abundance). In eutrophic, Optically Shallow coastal seascapes influenced by fresh water discharge, the phytoplankton was dominated by larger taxa (> 60 %). The seascape framework promises to be a tool to detect different biogeographic domains quickly, providing information about the changing environmental conditions experienced by coral reef organisms including coral, sponges, fish and higher trophic levels. The effort was conducted as part of the Sanctuaries Marine Biodiversity Observation Network (MBON) demonstration project and as part of the South Florida Ecosystem Restoration Research (SFER) project managed by the Atlantic Oceanographic and Meteorological Laboratory of NOAA (AOML-NOAA).