Questions answered

By Sherry Seethaler

SAN DIEGO UNION TRIBUNE
December 1, 2004

QUESTION: Are recent environmental threats to coral reefs from rising sea levels unfounded? In Panama's gulf on Isla Contadora last year we were stunned to find huge coral reefs alive and well where tidal range is more than 20 feet, in water so hot that it almost felt scalding upon entry. If El Nino caude "bleaching" due to excessively high temperatures, we utterly failed to find any evidence of it.

– Fred Crowe, San Diego

ANSWER: Your question identifies two possible threats to coral reefs, both of which are linked to global climate change: rising sea level and increase in seawater temperature. Sea level rise itself is not expected to devastate coral reefs. Larger waves may cause erosion of less protected reefs, but rising sea level also permits reefs to expand vertically.

On the other hand, temperature increases can lead to mass bleaching, as occurred in 16 percent of the world's coral reefs in 1998 (an El Niño year). Mass bleaching is believed to be a relatively recent phenomenon. Since 1979, there have been six such events.

Bleaching occurs when the individual coral polyps – the organisms that produce the limestone skeleton of the reef – lose the algae they harbor. The algae, called zooxanthellae, give the reef its color. The zooxanthellae also produce oxygen and food needed by the coral, in return for the coral's nutrient-rich waste products.

Although coral can recover after mild bleaching, the sensitivity of coral to temperature changes has led scientists to predict that half of the world's coral reefs could be lost by 2030. However, recent research shows that at least some bleached coral can recover by partnering with a more heat-tolerant species of zooxanthellae.

Coral reefs therefore seem to have some adaptability to climate change that scientists have not factored into their predictions. However, there is much uncertainty about the combined impact of temperature changes and other threats to reefs. For example, sewage damages coral by aiding inthe spread of diseases. Also, carbonic acid produced as levels of carbon dioxide in seawater increase can weaken coral skeletons.

When I was inserting my contact lenses, I noticed that I had a very tiny hole on the inside corner of my bottom eyelids. What are these holes?

– Brent Hannify, Poway

They are called puncta and are the openings to the tiny canals through which tears drain. Tears flow from these canals into a tear sac and then down the tear duct into the nose. In fact, you can taste eye drops after they flow from the puncta into your nose and drip onto the back of the tongue.

copyright 2004 The San Diego Union Tribune