Coral polyps have been caught taking turns embracing one another, a behavior known as coral polyp kissing, for the first time with the help of an underwater microscope.  Although not much is known about this phenomenon, researchers speculate the kissing corals engage in this act to exchange food or nutrients.

The discovery is part of a study by researchers from the Scripps Institution of Oceanography at the University of California San Diego and University of Haifa’s Charney School of Marine Science, who created the Benthic Underwater Microscope (BUM) to understand the never-before-seen ecological processes of the underwater world at a microscopic scale. Their findings were published on July 12 in the journal Nature Communication.

BUM contains a high-magnification lens, fluorescence imaging capabilities, a ring of focused LED lights for fast exposures and a flexible tunable lens to view structures in 3-D, similar to our eyes. This instrument allowed the researchers to study the creatures in their natural habitat instead of bringing them in the laboratories, which cannot provide scientists with other valuable information.

“This underwater microscope is the first instrument to image the seafloor at such small scales,” says co-lead author Andrew Mullen, a PhD student at Scripps. “The system is capable of seeing features as small as single cells underwater.”

Apart from kissing corals, the researchers also observed coral turf war in the Red Sea. When a species of corals competes for seafloor space with another species, these corals produce string-like filaments that emit enzymes from their stomach to destroy the tissue of the other coral. However, when the research team placed corals with the same species close together, they did not do the same action, showing that the corals can recognize their enemies and friends.

They also observed one of the largest coral bleaching events on record off Maui in Hawaii. This is the result when corals lose their colors due to rising temperatures or environmental stressors like pollutants.

The next step for the team is to take photos of microscopic particles in the water near the surface of the corals. This could give insight into how corals breathe.