The stunted growth of coral reefs.

 
New York City shelters its 8.3 million residents within a complex, three-dimensional matrix of concrete and steel. Construction crews must work on the integrity of the city’s structural skeleton constantly just to keep up with growth and age. Like a living organism, the city is expanding up, down and outwards while repairing and replacing decrepit trusses and frames with new, high quality materials.

It is a common big-screen fantasy to imagine the physical decay of New York City if these construction efforts were to suddenly cease in some kind of post-apocalyptic madness. However, the structural collapse that would bring New York City back to nature is actually occurring within nature, and you don’t need CGI graphics to imagine it. Just last week a team of scientists shared new findings that warming oceans are reducing the size and strength of coral reefs in two different parts of the world.

A coral reef is not unlike a city. Reefs are massive underwater edifices that support a stunning diversity and density of organisms. But instead of using building materials like concrete and steel, coral reefs house their residents within and upon a skeleton of calcium carbonate. This calcium carbonate is continually laid down by the reef's construction crew – growing colonies of coral polyps.

Individual coral polyps are actually small, soft-bodied animals that grow affixed to a hard surface. For protection they secrete calcium carbonate near their base. This calcium carbonate accumulates as the polyps grow, clone themselves, and multiply into large colonies. Over many generations, the calcium carbonate left behind becomes the skeleton of the reef, which still consists of a living colony of coral polyps on the surface.

The ability of coral polyps to produce calcium carbonate, called calcification, depends on a host of environmental factors. For example, seasonal differences in water temperature cause calcification to increase in the summer and decrease in the winter, resulting in alternating layers of high and low calcium carbonate density. It creates a pattern similar to the annual growth rings of a tree. The scientists used this pattern to measure the extent of growth and the density of calcium carbonate produced every year by coral colonies. They focused on two genera, Porites and Montastraea, from the Great Barrier Reef and Mesoamerican Barrier Reef. They compared these annual growth data to existing records of warming sea surface temperatures spanning at least a decade.

One of the coral genera, Porites, showed the greatest sensitivity to warming temperatures regardless of location. In both the Great Barrier Reef and the Mesoamerican Barrier Reef, Porites experienced sharp declines in calcification rate as sea surface temperatures increased. If climate change models are correct, at the given rate of decline, Porites in the Great Barrier Reef will stop laying down calcium carbonate entirely by 2100. In the warmer Mesoamerican Barrier Reef, calcification by Porites will cease in 2060. The genus Montastraea has also experienced reduced rates of calcification, although not as extreme. Montastraea in the Mesoamerican Barrier Reef will experience a 40% reduction in calcification by 2100.

The consequences of reduced calcification will manifest differently in the two genera. As temperatures rise, Porites produces calcium carbonate at the same density, but compensates for reduced calcification by not extending as far. Therefore, Porites reefs will grow more slowly and could be outcompeted for space by other organisms. Montastraea continues to extend in warmer temperatures, but it does so at the expense of calcium carbonate density. Much like osteoporotic bones, a Montastraea reef with reduced calcium carbonate density is more susceptible to physical and biological damage. Warming water temperatures will compromise both types of reefs in their ability to support biodiversity, either in terms of space or strength.

As grim as they seem, these predictions are likely conservative. The scientists mention that they don’t consider other factors that affect calcification such as coral mortality, coral bleaching, disease, and the negative consequences of pollution, erosion and other environmental concerns. The slow decline of coral reefs may not be fodder for a disaster flick, but piles of stunted, brittle coral reef will be utterly disastrous for the world’s oceans in a time that is already considered a biodiversity crisis.

Carricart-Ganivet JP, Cabanillas-Tera´n N, Cruz-Ortega I, Blanchon P (2012) Sensitivity of Calcification to Thermal Stress Varies among Genera of Massive Reef-Building Corals. PLoS ONE 7(3): e32859. doi:10.1371/journal.pone.0032859 

Photo: A view of the Mesoamerican Barrier Reef, Belize en.mesoamericanreef.org

A hurricane to Tip the scale.

Tonight New York City is bracing for Hurricane Irene, and while the storm will undoubtedly deliver aggressive winds and major flooding, the level of panic is a little excessive for a fading Category 1 hurricane. Don’t get me wrong, people should take all necessary precautions, and those New Yorkers in Zone A should certainly obey evacuation orders. As Governor Christy says “Get the hell off the beach,” you’ve maximized your tan. I just think that come Monday, people may feel a little bit silly for clearing out the grocery stores of every last crumb of bread and drop of milk.

Although the memory of Hurricane Katrina is still fresh (even more so for fans of Treme), New York City on Monday morning will still resemble New York City, not a post-Katrina New Orleans. Let’s get some perspective. Hurricanes, or tropical cyclones as they are known worldwide, are characterized by a region of extreme low pressure at the center that is surrounded by thunderstorms, causing powerful winds and heavy rain. The lower the pressure and the stronger the winds, the more intense the storm. The Saffir-Simpson Hurricane Scale only categorizes storms by wind speed, although central pressure is also a good indicator of hurricane strength.

Right now, Irene is hanging out about 100 miles south of Ocean City, Maryland. The average sustained wind speed is 80 mph, which makes it a Category 1 storm, and the pressure at the eye of the storm is 951 millibar. When the winds slow to 73 mph, it will become a tropical storm. When Hurricane Katrina hit New Orleans on August 29, 2005, it was a Category 3 storm with sustained winds of 125 mph and pressure of 920 millibar.

Katrina was the costliest tropical cyclone ever, with damage exceeding $100 billion. It also was one of the deadliest, claiming 1836 lives. But let’s talk about another storm. The most intense tropical cyclone ever was Typhoon Tip in 1979. Tip was positioned in the north western Pacific Ocean, and it made landfall on Guam and southern Japan. Although it didn’t claim as many lives as Katrina, the statistics are staggering. The highest sustained winds were 190 mph for one minute and 160 mph for ten minutes. The pressure at the eye of the storm reached an unheard of 870 millibar. It was also the largest storm ever, extending 1380 miles across, which is half the area of the continental United States. Typhoon Tip had such extreme winds, that it ranks as a hypothetical Category 6 on the Saffir-Simpson Scale. This means that the storm’s potential damage is beyond catastrophic.

Hurricane Irene may damage some roofs and fell trees, but we will emerge relatively unscathed. In comparison, read the description of a Category 5 hurricane below:

"People, livestock, and pets are at very high risk of injury or death from flying or falling debris, even if indoors in mobile homes or framed homes. Almost complete destruction of all mobile homes will occur, regardless of age or construction. A high percentage of frame homes will be destroyed, with total roof failure and wall collapse. Extensive damage to roof covers, windows, and doors will occur. Large amounts of windborne debris will be lofted into the air. Windborne debris damage will occur to nearly all unprotected windows and many protected windows. Significant damage to wood roof commercial buildings will occur due to loss of roof sheathing. Complete collapse of many older metal buildings can occur. Most unreinforced masonry walls will fail which can lead to the collapse of the buildings. A high percentage of industrial buildings and low-rise apartment buildings will be destroyed. Nearly all windows will be blown out of high-rise buildings resulting in falling glass, which will pose a threat for days to weeks after the storm. Nearly all commercial signage, fences, and canopies will be destroyed. Nearly all trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Long-term water shortages will increase human suffering. Most of the area will be uninhabitable for weeks or months." From the National Weather Service.

The above photograph is pretty much the reason for this whole post. Courtesy of KeystoneUSA-Zuma/Rex Features.