Coral stays healthy by internal ocean flow within colony

Corals rely on the flow of water around them to carry nutrients and waste to and from their living polyps. While it is known that coral polyps on the outside of a reef receive a greater hydrodynamic flow than those in the interior, researchers at Virginia Tech found the rate of nutrient and waste transfer was nearly equal in both locations.

The geometry of a coral is determined by its stony skeleton, which is built by the polyps when they secrete calcium carbonate onto their existing structure. The researchers found while water velocities on the inside of the coral colony are up to slower 64% by virtue of the colony design, the rate of mass transfer remained essentially constant throughout the colony.

Researcher Anne Staples said understanding the relationship of flow hydrodynamics from the surrounding ocean to the hydrodynamics inside the coral could teach us how to maintain the health of remaining coral colonies in our oceans.

“It is known that increased ocean acidity, pollution, and temperatures are bad for coral health,” Staples said. “The more we know about how the conditions in the interiors of coral colonies and reefs relate to the surrounding ocean conditions, the more effectively we can design interventions to safeguard coral health.”

The researchers are planning to investigate how the ocean hydrodynamics affects colonies with different geometries. They believe that understanding the detailed flow characteristics in a reef will enable the development of more precise mathematical models that can effectively bridge the gap between coral and ocean hydrodynamics and lead to insights in many critical areas of inquiry, like nutrient uptake, reef growth rates and bleaching.

Source: “Passive vortical flows enhance mass transport in the interior of a coral colony,” by Md Monir Hossain and Anne E. Staples, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5094076 .