Microbes are integral to the structure and functioning of marine ecosystems, and to the chemistry of the ocean and its interaction with the atmosphere. They mediate the chemical transformations that over geological time have determined the composition of our atmosphere (Fennel et al., 2005) and the balance of major nutrients in the sea (Arrigo, 2005). These nutrients ultimately determine how much and what kinds of marine life can be supported in surface waters, the amount of primary production that can be transferred to higher trophic levels, and how much carbon is stored in the deep ocean (Falkowski et al., 1998). Microbes in the ocean are thus directly and indirectly sensitive to, and part of, the ocean’s response to global change. The manifestations of global change include not only the changes in ocean temperature, circulation, pH, and nutrient availability linked to increasing greenhouse gases, but also the profound alterations of the marine environment associated with a growing and rapidly developing human population—habitat destruction, coastal eutrophication, pollution (GESAMP, 2001), and the elimination of larger predators by fishing, leading to fundamental alterations in food webs (Pauly et al., 1998; Myers et al., 2007).