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Cement helps, but coral will need time to repair


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POSTED: Monday, July 20, 2009

What does it take to put thousands of coral heads back together again?

A couple of things the king's horses and king's men did not have: scuba gear and cement.

When Navy divers recently reattached thousands of coral colonies to a reef damaged by a Navy ship that went aground in February, several readers wondered what you use to glue down thousands of broken coral heads.

I wondered, too. In this case, experts chose a common kind called Portland Type II cement.

Portland cement has nothing to do with Oregon.

In 1824 a British stonemason heated some limestone, clay and water on his kitchen stove. After drying, it looked like a kind of stone found on the Isle of Portland, a peninsula in the English Channel. The bricklayer called his invention Portland cement. Today, dried, we call it concrete.

Portland cement comes in eight mixtures, each with slightly different characteristics such as setting time, strength and resistance to certain chemicals.

The Type II used to mend the coral heads is resistant to sulfur, a natural mineral in sea water that degrades concrete.

The kinds of corals the ship damaged are typical of most of Hawaii's reefs. The most common are lobe (mounds and lumps), finger (pointy), cauliflower (small heads), rice (bumpy sheets and plates) and sandpaper rice (smooth sheets and plates).

The grounded ship and its rescue efforts broke coral heads from tiny to the size of a VW Beetle, at 9 to 45 feet deep, in an area of six to 10 acres.

About 80 percent of the damage came from the cables on rescue vessels. Those heavy lines dragging over the bottom acted like weed whackers, a state Department of Land and Natural Resources biologist told me, lopping off everything in their paths.

During high surf conditions, the resulting rubble will bang into and damage the area's remaining coral heads. Navy divers removed about 250 cubic yards of it. Still, some wreckage remains, and like all living organisms, corals can only take so much stress.

Of the colonies that were not killed by collisions, many were uprooted, tumbled, stepped on and handled. This evicted the reef's resident crabs, shrimp and other animals that defend the corals from predators.

And the corals need their feisty tenants more than ever at a time like this. When traumatized, corals release cellular fluids into the water. If crown-of-thorns starfish and cushion stars, both coral eaters, detect these chemicals, they come a-running.

The small coral colonies broken in the accident are lost, but now more than 5,400 of the larger ones are glued with Portland cement to the stony bases left on the ocean floor.

Only time will tell whether this repair effort worked, because coral reef-making is a massive endeavor that moves at a glacial pace. For instance, a 15-foot-wide head of lobe coral, one of Hawaii's most common reef-building species, contains about 25 million individuals, and adds about one-fourth of an inch per year to its colony. Such a coral head would be about 300 years old.

As a sailor and skipper, my heart aches for this ship, its commanders and its crew. I know how easy it is for things to go wrong at sea. As a Hawaii resident, biologist and lover of marine life, my heart also aches for the damaged corals and their displaced residents.

The Navy and corals had a great fall. I wish both the cementers and the cemented all the best.

 

Susan Scott can be reached at www.susanscott.net.