Preliminary investigation of Synechococcus sp and Prochlorococcus sp of South Western Western Australia

The west coast of Australia represents a unique environment in which to study marine organisms as the major cur-rent, the Leeuwin Current, flows pole-wards rather than equator-wards like all other eastern boundary currents. This current is stronger in winter and during summer the coastal Capes Currents develops. These currents influence the physical and chemical properties of the water column and thus the distribution of picoplankton in general. The data presented here represents the first quantification of picoplankton on the coast of Western Australia using flow cytometry and is composed of two sections. Firstly, as part of the Strategic Research Fund for the Marine Environment, three sites were sampled to determine microzooplankton grazing, on an inshore/offshore transect, evaluating their bactivory on Synechococcus sp. and Prochlorococcus sp. In addition samples were collected from the long term CSIRO monitoring station west of Rottnest Island to examine the vertical distribution of Synechococcus sp. and Prochlorococcus sp. The abundance of Synechococcus sp. and Prochlorococcus sp. were within the lower ranges reported in the literature, whilst the transect stations had an order of magnitude more cells than the RNI station. Carbon was also within the lower ranges reported in the literature. Synechococcus sp. and Prochlorococcus sp. were both grazed at >100% across the transect. At the inshore station, Synechococcus sp. experienced exceptional grazing pressure. Grazing pressure was responsible for preventing accumulation of these species in this region, both onshore and offshore. Synechococcus sp. was more abundant than Prochlorococcus sp. at Rottnest Island (RNI) station. The vertical distribution of both species showed a maxima at 30 m depth below the thermocline and in approximately 4–5% surface irradiance. These preliminary findings suggest that Synechococcus sp. and Prochlorococcus sp. are found in similar quantities to other oligotrophic regions of the world and contribute to the microbial food web