Whirring over a sun-streaked patch of tropical sea floor, a submersible equipped with cameras is helping scientists map the struggling coral reefs off this U.S. Caribbean territory, a step toward preserving them.
The small machine, tethered to a 187-foot (57-meter) survey ship, was remotely steered over coral hills, sending a fisheye view back to scientists who hope the images will help them learn how to restore the weakened reefs.
The video and multi-beam sonar imagery taken this week provided the most exact charts ever of coral contours and sea floors in the area.
"It's neat getting the images because some of these spots are where Captain Cook's ships were once dropping lead lines to get an idea of what was down there," said researcher Mike Stecher, referring to the centuries-old practice of lowering weighted lines to map depth.
Scientists and observers in a control room on the Nancy Foster, a boat operated by the National Oceanic and Atmospheric Administration, oohed and aahed as grouper and squirrel fish darted behind coral or sponges before the lens of the submersible.
The maps generated by the expedition along Puerto Rico's coast will help gauge the health of dwindling coral habitats, some of which have been "bleached" and killed by climate change, according to the mission's chief investigator, Tim Battista.
Reef-building coral, a tiny polyp-like animal that builds a calcium-carbonate shell around itself, provides important refuge, breeding and feeding areas for thousands of types of marine creatures. But it is under assault in the Caribbean and across the globe.
In Puerto Rican waters, shallow-water reefs have been harmed by pollution and overfishing. Nearly half of the coral in areas of the neighboring U.S. Virgin Islands died from diseases after months of warming waters in 2005.
Researchers have predicted that as much as 60 percent of the world's coral could die by 2030 if ocean temperatures and pollution levels continue to inch upward. Carbon dioxide and other greenhouse gases contribute to rising sea temperatures that are damaging the reefs.
NOAA marine biologist Mark Monaco said the agency has been undertaking the most extensive mapping study ever of reefs, covering U.S. territories in the Atlantic and Pacific.
"Coral reef ecosystems that we see today clearly have many stressors. You can't pull down big ice cubes to help stop warming oceans, but we have a responsibility as humans to preserve these habitats," Monaco said aboard the NOAA research vessel.
Monaco said the fragile areas can be protected by enforcing rules against overfishing, runoff from coastal developments and the impacts careless dropping of anchors.
The new NOAA maps will also help in fish conservation because devices aboard the Nancy Foster can emit sonic waves to count fish, letting researchers chart how they are distributed, said Laura Kracker, a NOAA scientist aboard the research boat.