Journal of the Marine Biological Association of the UK

Research Article

Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel

William H.  Wilson a1c1, Glen A.  Tarran a2, Declan  Schroeder a1, Michael  Cox a3, Joanne  Oke a1 and Gillian  Malin a4
a1 Marine Biological Association, Citadel Hill, Plymouth, PL1 2PB
a2 Plymouth Marine Laboratory, Prospect Place, Plymouth, PL1 3DH
a3 Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL
a4 School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ


This study used analytical flow cytometry (AFC) to monitor the abundance of phytoplankton, coccoliths, bacteria and viruses in a transect that crossed a high reflectance area in the western English Channel. The high reflectance area, observed by satellite, was caused by the demise of an Emiliania huxleyi bloom. Water samples were collected from depth profiles at four stations, one station outside and three stations inside the high reflectance area. Plots of transect data revealed very obvious differences between Station 1, outside, and Stations 2–4, inside the high reflectance area. Inside, concentrations of viruses were higher; E. huxleyi cells were lower; coccoliths were higher; bacteria were higher and virus:bacteria ratio was lower than at Station 1, outside the high reflectance area. This data can simply be interpreted as virus-induced lysis of E. huxleyi cells in the bloom causing large concentrations of coccoliths to detach, resulting in the high reflectance observed by satellite imagery. This interpretation was supported by the isolation of two viruses, EhV84 and EhV86, from the high reflectance area that lysed cultures of E. huxleyi host strain CCMP1516. Basic characterization revealed that they were lytic viruses approximately 170 nm–190 nm in diameter with an icosahedral symmetry. Taken together, transect and isolation data suggest that viruses were the major contributor to the demise of the E. huxleyi population in the high reflectance area. Close coupling between microalgae, bacteria and viruses contributed to a large organic carbon input. Consequent cycling influenced the succession of an E. huxleyi-dominated population to a more characteristic mixed summer phytoplankton community.

(Received December 3 2001)
(Accepted April 19 2002)

c1 Corresponding author, e-mail: