Coral, get ready for your close-up
A new tool lets researchers zoom in on coral-reef health.
It’s a hard-knock life for a coral. Pesticides, oil spills, ships, and climate change are just a few of the punches that humans have thrown at reefs. With that in mind, Ph.D. student Miriam Weber of the Max Planck Institute for Marine Microbiology (Germany) started looking for a way to study corals in their ocean home instead of in the lab, where they’re hard to keep alive.
After 2 years of work, the result is a new diver-operated tool to diagnose exactly what’s ailing reefs, down to the decimal point. The microsensor profiler, as it’s called, is described in new research published in ES&T (DOI es070200b).
Weber’s motorized profiler uses microsensors to measure oxygen, hydrogen sulfide, pH, calcium, light levels, and other environmental conditions that could challenge the survival of corals or help them thrive. Each measurement is precise to within 5 micrometers (μm)—a grain of salt is about 70 μm in diameter. This means that an experienced diver can use a magnifying glass and maneuver the probe right into the mouth of an individual polyp.
“No microsensor system existed that I could deploy on a coral reef, so I knew I had to design one myself,” Weber says. The new device functions underwater down to 30 meters, allowing divers to collect data without returning to the surface. Its tiny, pointed feet also permit divers to deploy it on the uneven, fragile surfaces of a coral reef.
So far, the institute’s microsensor research team, led by Dirk de Beer, has used the system to study the effects of human-induced sedimentation on fragile reefs. In the Great Barrier Reef lagoon off the coast of Australia, sediment loads are 10 times higher now than before settlers arrived 200 years ago. In addition, extensive grazing by livestock and farming of sugarcane crops have leaked nutrients from soil to coastal waters and have displaced coastal vegetation that would otherwise hold sediments on land.
With the help of the new microsensor system, the team discovered that sediments flowing into reefs damage coral not only by blocking light, a known mechanism, but also by suffocating tiny coral polyps of oxygen and, according to new unpublished data, consequently poisoning them with toxic sulfide. This means that loads of nutrient-rich sediments can kill coral within 24 hours, much more quickly than previously thought. Today, nearly 60% of coral reefs worldwide are threatened by sedimentation, Weber says.
Kay Vogel of the National Institute of Water and Atmospheric Research (New Zealand) is eager to try out the new device. He uses microsensors to understand the boundaries between living systems and water to show, for example, that microbial mats under Antarctica’s floating ice are alive. “I would use this in my own research,” he says, noting that he now has to transmit each data point laboriously to a shipboard crew, and someone on board writes it down.
The setup comes with fun accessories: a magnifying glass, an underwater flashlight, and a paintbrush accompany the motor, micromanipulator, and microsensor. To tote it all, “I need something really small in a little suitcase that I can take with me and look for just the right spot,” Weber says.
The kit is not sold in stores, but any researcher can build a profiler using the instructions in the paper and supporting materials. In fact, Weber encourages other marine scientists to borrow her design, “so we can learn much more about what is really happening down there.”
