Future and emerging pervasive computing systems call for new service models and coordination approaches enforcing self-organisation as an inherent property of component interaction. We introduce the concept of a pervasive ecosystem, and present the coordination approach grounded upon it, which revolves around (i) the notion of a distributed and dynamic space of “live semantic annotations” (wrapping data, knowledge, and activities of humans, devices, and services) and (ii) a set of chemical-resembling coordination rules that are applied to such annotations semantically. As an application example we present a simulated scenario of crowd steering in an exhibition centre.