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What intricate baskets of Venus flowers manipulate the flow of sea water

A basket of Venus flowers is not quite a spectacle. This stunning deep water sponge can also alter the flow of seawater in amazing ways.

A barrel-shaped lace chamber forms the glassy skeleton of the sponge. Flow simulations reveal how this intricate structure alters the way water moves around and through the sponge, helping it withstand unforgiving ocean currents and perhaps feed and reproduce, researchers reported online on July 21 in Nature .

Previous studies have found that the grid-shaped construction of a basket of Venus flowers (Euplectella aspergillum) is strong and flexible. “But no one has tried to see if these beautiful structures have dynamic fluid properties,” says mechanical engineer Giacomo Falcucci of Tor Vergata University in Rome.

Taking advantage of the supercomputers, Falcucci and his colleagues simulated how water flows around and through the body of the sponge, with and without different skeletal components such as the countless pores of the sponge. If the sponge were a solid cylinder, the water flowing later would form a turbulent wake immediately downstream that could push the creature, Falcucci says. Instead, water flows in and around the highly porous Venus flower basket and forms a soft zone of water that flanks the sponge and shifts the turbulence downstream, the team discovered. This way, the sponge body withstands less stress.

The ridges that exhale around the outside of the sponge skeleton also cause the water to slow down and turn inside the structure, the simulations showed. As a result, food and reproductive cells that flow into the sponge will be trapped up to twice as long as in the same ridge-free sponge. That persistence could help filters capture more plankton. And because Venus flower baskets can reproduce sexually, they can also increase the chances of floating sperm finding eggs, the researchers say.

It’s amazing that beauty can be so functional, says Falcucci. Sponge flow alteration skills, he says, can help inspire taller, wind-resistant skyscrapers.

This simulation shows how water flows around and through a basket of Venus flowers (gray). The ridges that exhale on the outside of the sponge cause the water inside to soften and rotate in some way, forming particle trapping vortices. And the shape of the sponge creates a softer zone of slower water that forms immediately downstream, cushioning the creature against turbulence. The vertical cross sections contrast the flow activity of the quiet zone (closest to the sponge) and the turbulent zone (downstream).G. Falcucci et al / Nature 2021

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