Sea surface microlayer and bacterioneuston spreading dynamics

The sea surface microlayer (SSM) has been well studied with regard to its chemical and biological composition, as well as its productivity. The origin and dynamics of these natural communities have been less well studied, despite extensive work on the relevant physical parameters, wind, turbulence and surface tension. To examine the effect these processes have on neuston transport, measurements of wind-driven surface drift, surfactant spreading and bacterial transport in the SSM were made in the laboratory and in the field Spreading rates due to surface tension were up to approximately 17 km d ¹ (19.7 cm s^-1) and were not significantly affected by waves. Wind-induced surface drift was measured in the laboratory. Wind speeds of 2 to 5 m s^-1 produced drift speeds of 8 to 14 cm s^-1, respectively. We demonstrate that bacteria spread with advancing slicks, but are not distributed evenly. Localised concentrations were found at the source and at the leading edge of spreading slicks. The Reynolds ridge, a slight rise in surface level at the leading edge of a spreading slick, may provide a mechanism by which bacteria are concentrated and transported at the leading edge. Bacteria already present at the surface were not pushed back by the leading edge, but incorporated and spread evenly across the slick. The spreading process did not result in the displacement of extant bacterioneuston communities. The results indicate surface tension and wind-induced surface drift may alter distributions and introduce new populations into neustonic communities, including communities distant from the point source of release.