Plankton are rather like soil microorganisms in that many thousands of species form the bottom of the food chain on sea and on land. This may mean that by the time we are ready to seed life onto Mars’ surface (once it has been terraformed with atmosphere and oceans) we may find that there are just too many microorganisms to reanimate directly from DNA sequences in computer memories. Therefore given that Mars is a cold planet and most of the plankton and microorganisms we will be trying to introduce will be cold tolerant, it seems sensible to bring samples from earth in frozen form. For soils this would be a filtered first to get rid of the sand and gravel, and for plankton it would need to be filtered to increase the number of species collected.
Other issues which would need to be considered would be which types of microorganisms and plankton to introduce first. For plankton this would mean phytoplankton which could use sunlight, carbon dioxide, water and minerals in the water to create plant tissue.
However the survival rate of the organisms in these samples is likely to be low, so repeated sample additions may allow an ecosystem to develop layer by layer. So the first survivors would be able to survive in isolation using inorganic resources, and the last would be predators which would need a rich micro ecosystem to be in place for their survival.
charlesjoynson 