Phytoplankton, accounting for less than 1% of the Earth´s biomass but almost 50% of annual marine net primary production, plays a critical role in global carbon cycling. Mechanisms that control their mortality are, however, still poorly understood, and th e current project, VIPMAP, seek to generate new knowledge of two such mechanisms: 1) Lysis of marine phytoplankton caused by viral infection and 2) programmed cell death (PCD), and will explore relations between the two mechanisms. VIPMAP aims at improvin g methods for determining algal virus diversity. Methodology for identification and quantification of algal viruses and for detecting PCD in situ will also be developed. In order to reach the goals VIPMAP will integrate three internationally high-quality research groups and combine advanced molecular (sequencing, quantitative PCR, biochemical (determination of metacaspase protein levels (via western blot analysis) and metacaspase gene expression (via q-RT-PCR)) and technological methodology (flow cytomet ry with cell sorting). The methods will be applied in situ to increase our understanding of mortality mechanisms in different phytoplankton species and thereby gain a better understanding of why some phytoplankton species form extensive blooms whereas oth ers do not. VIPMAP ´s contribution to society as such is apparent in view of the fact that correct understanding of control mechanisms in the lower part of the pelagic food web is necessary to correctly assess a wide range of socio-economically important aspects of the marine ecosystem such as biodiversity and plankton dynamics, harmful algal blooms and global change research. Moreover, the methodology developed may prove useful for other areas of marine research such as ballast water treatment, detection of and understanding harmful algal blooms, fish-and shellfish farming, e.g. detection of fish- and/or shellfish pathogenic agents.