There are two ways of assessing the costs of environmental degradation: as the costs associated with the loss of benefits resulting from the degradation of natural capital, and as the maintenance costs required to compensate for the actual or potential degradation of natural capital. The first of these methods is based on the Total Economic Value (TEV) of benefits forgone because of the depletion of ecosystem services delivered by marine biodiversity. The second method is based on the costs required to maintain a good state of marine biodiversity, one which makes it possible to deliver ecosystem services. This paper gives an illustration of this second approach. It details how these maintenance costs have been calculated in the initial assessment of the Marine Strategy Framework Directive (MSFD) in France. It addresses nine problem areas – corresponding to nine sources of environmental degradation – from non-native invasive species to oil spills. It gives a total figure for these degradation costs (around 2 billion Euros). The results are compared with those of other Member States who have taken similar approaches in the context of the MSFD. One key conclusion is that it is not really possible to make meaningful comparisons at this stage, since the methods of data collection and the nature of the costs are very different. The need to develop such assessments in a standardised way is noted.