We are interested in the problem of coexistence of many species consuming the same limiting resource. It is clear that a periodically returning optimal limiting resource (i.e. each species consumes its own portion of the limiting resource) supports coexistence. Our theory is that a periodically returning quasi-optimal limiting resource (i.e. each species mainly consumes its own portion of the limiting resource, but also consumes some of other species’ portions) also supports coexistence. To verify our theory, we introduce a natural mathematical model on the population dynamics of many species of plankton consuming a periodically returning quasi-optimal limiting resource. Our numerical simulations show that in this case, these species of plankton can coexist even when the quasi-optimality is quite far away from optimality. This is another mechanism toward the resolution of the paradox of plankton. Field collection of data shows that lake resource of plankton tends to be patchy with each patch mainly consumed by one species but also shared with other species