Submersible maps seafloor to probe health of coral reefs

Aboard the Nancy Foster off the coast of Puerto Rico -- Whirring over a sun-streaked patch of tropical seafloor, a submersible equipped with cameras is helping to provide the most detailed maps ever recorded of underwater shelves and struggling coral reefs off this U.S. Caribbean territory.

The small machine, tethered to a 187-foot survey ship, was steered by remote over coral hills, sending a fish-eye view back to scientists who studied the images in hopes of restoring reefs weakened by manmade and natural threats. More exact contours were mapped in an hour by video and multibeam sonar imagery than was ever charted before 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 oohed and aahed as they watched a sporadic grouper or squirrel fish dart behind coral or sponges on images sent by the submersible to a control room on the Nancy Foster, a ship operated by the National Oceanic and Atmospheric Administration.

The maps generated by the NOAA team during an expedition along coastal stretches of Puerto Rico 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 polyplike animal that builds a calcium-carbonate shell around itself and provides important refuge, breeding and feeding areas for thousands of marine creatures, is under assault in the Caribbean and across the globe.

In Puerto Rican waters, shallow-water reefs are stressed badly by coastal pollution and overfishing. Nearly half of the coral in areas of the neighboring U.S. Virgin Islands died from disease outbreaks after months of warming waters in 2005.

Researchers have predicted that up to 60 percent of the world's coral could die by 2030 if ocean temperatures and pollution levels continue to inch upwards. Carbon dioxide and other greenhouse gases contribute to rising sea temperatures that are damaging the reefs.

NOAA marine biologist Mark Monaco said the U.S. agency has been undertaking the most extensive mapping study ever of reefs from the Atlantic to the Pacific using a wide variety of imaging systems to support natural resource management and save dwindling reefs.

"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.

A key, Monaco said, is to protect these fragile areas from damaging pressures by enforcing rules against overfishing, runoff from coastal developments, and the impacts of anchors.

New NOAA maps will also aid government authorities in fish conservation because hydroacoustic devices aboard the Nancy Foster can emit sonic waves underwater to count fish and chart how they are distributed, said Laura Kracker, a NOAA scientist aboard the research ship.

Source : http://www.sfgate.com/