Surface flow for colonial integration in reef-building corals

Reef-building corals are endangered animals with a complex colonial organization. Physiological mechanisms connecting multiple polyps and integrating them into a coral colony are still enigmatic. Using live imaging, particle tracking, and mathematical modeling, we reveal how corals connect individual polyps and form integrated polyp groups via species-specific, complex, and stable networks of currents at their surface. These currents involve surface mucus of different concentrations, which regulate joint feeding of the colony. Inside the coral, within the gastrovascular system, we expose the complexity of bidirectional branching streams that connect individual polyps. This system of canals extends the surface area by 4-fold and might improve communication, nutrient supply, and symbiont transfer. Thus, individual polyps integrate via complex liquid dynamics on the surface and inside the colony. [Display omitted] •Surface-associated currents connect individual polyps in a coral colony•Surface currents show species-specific topography, complexity, and speed variation•Mucus plays a role in surface currents to different extent depending on the species•Complex flow in the gastrovascular system further integrates individual polyps Bouderlique et al. reveal a new way of integrating individual coral polyps via complex-surface-associated currents. These mucus-containing currents show species-specific patterns connecting individual polyps, removing debris to keep the surface clean and to help polyps to control individual feeding territories on the colony’s surface.