An underwater microscope allows researchers to capture behaviours of corals and other marine organisms in their native habitats.

Credit: L: Emily L. A. Kelly/R: Andrew Mullen

Andrew Mullen at the Scripps Institution of Oceanography in La Jolla, California, and his colleagues designed a system (pictured left) that divers can use to take almost micrometre-resolution images (Stylophora coral pictured right) at depths of up to 30 metres. It lets marine biologists observe biological processes on the sea floor that cannot be easily replicated in a lab.

The authors used their instrument to study millimetre-sized coral polyps off the coast of Maui, Hawaii, in 2015, during the first mass coral-bleaching event recorded for the main Hawaiian islands. They found that algae colonized bleaching corals in specific patterns. Near Eilat in Israel, they discovered that coral polyps connect to each other through their openings, probably to share chemicals.

Nature Commun. 7, 12093 (2016)