Effect of Solar Radiation on Presence and Abundance of Surfactant Associated Bacteria in the Sea Surface Microlayer

The sea surface microlayer (SML) is the boundary layer at the surface of the ocean, distinct from the water below and highly variable in space and time. SML is influenced by organisms that aslicks. Slicks are the result of surfactants dampening capillary waves, which can be seen in synthetic aperture radar (SAR) imagery because the smooth surface reflecting backscatter away from the receiver. This experiment investigated the presence and abundance of surfactant-associated bacteria in the SML above a coral reef and in slicks in a coastal seagrass ecosystem. During the experiment in the Florida Keys, 220 SML and subsurface water (SSW) samples were collected above a coral reef area and in slicks above a coastal seagrass ecosystem. During our previous experiments in the Gulf of Mexico samples were collected in the daylight only; while, in the Straits of Florida, in both daylight and nighttime (due to the study of the coral sponging, which however did not happen at the time of the experiment). All SML and SSW samples were sequenced on the Illumina MiSeq, 12 surfactant associated bacteria genera were found. Increasing wind speed had a negative effect on the abundance of these genera, with lower wind speeds showing a more habitable environment. The ratio of abundance of surfactant-associated bacteria between the SML and SSW was found different and affected by the ultraviolet component of solar radiation. Thus, the concentration of bio-surfactants in the SML may be different during the daylight and nighttime with corresponding consequences for the SAR imagery and air-sea interactions.