Underwater microscopy

Benthic Underwater Microscope

Many important biological processes in the ocean take place at microscopic scales, but when researchers remove organisms from their native habitats to study them under laboratory conditions, much of the information and its context are lost.

Colleagues from the Scripps Institution of Oceanography in San Diego have developed a new type of underwater microscope to image marine microorganisms in their natural settings without disturbing them. The Benthic Underwater Microscope, or BUM, is a two-part system.  An underwater computer with a diver interface tethered to a microscopic imaging unit allows researchers to study marine subjects at nearly micron resolution. The instrument has a high magnification lens, a ring of focused LED lights for fast exposures, fluorescence imaging capabilities, and a flexible tunable lens, similar to the human eye, to change focus for viewing structures in 3-D.

To test the new technology's ability to capture small-scale processes the imaging system was used to view millimeter-sized coral polyps off the coast of Israel in the Red Sea, and off Maui, Hawaii. During the experiments in the Red Sea, the researchers set up the BUM to capture the interactions of two corals species placed close to each other. The images revealed processes in which corals emit string-like filaments that secrete enzymes from their stomach cavity to wage a chemical turf battle to destroy the tissue of other species in a competition for seafloor space. 

The team also looked at temporal processes such as the algal colonization and overgrowth of bleaching corals. Off Maui they followed one of the largest coral-bleaching events on record, which occurs when single-celled algae that live inside the coral polyp eject themselves during high ocean temperature events. Recently bleached corals are still alive, but in their weakened state can be rapidly invaded and overgrown by filamentous turf algae. Using the microscope, the research team observed a previously unreported honeycomb pattern of initial algal colonization and growth in areas between the individual coral polyps during coral bleaching.

This underwater microscope is the first instrument to image the seafloor at such small scales. The system is capable of seeing features as small as single cells underwater. This instrument is a part of a new trend in ocean research to bring the lab to the ocean, instead of bringing the ocean to the lab.