Human Activities Threaten Coral Reefs

发布于:2011-03-15 17:13

分类于:VOA慢速英语 | 来源:飞达广播网

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BOB DOUGHTY: This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty.
FAITH LAPIDUS: And I'm Faith Lapidus. Today we tell about threats to coral reefs and some new discoveries about these ancient, biological structures.
BOB DOUGHTY: Corals are groups of small organisms called polyps. Millions of polyps grow together to form coral reefs. America's National Oceanic and Atmospheric Administration, NOAA, says the coral reefs that exist today are up to fifty million years old. The ancestors of these reefs were formed at least two hundred forty million years ago.
However, human activities are threatening the world's coral reefs. NOAA scientists say the main threats are pollution, overfishing and climate change. As a result, coral reef populations are decreasing worldwide.
NOAA says an estimated twenty percent of the reefs have been damaged beyond recovery. About fifty percent of the remaining coral are under risk of collapse.
FAITH LAPIDUS: Now there is a new threat facing coral reefs in the Caribbean Sea. The threat comes from another sea creature.
A recent study found that damselfish are killing head corals in the Caribbean. Researchers say this is creating even more problems for the area's already troubled coral reefs. The journal PLoS ONE published a report about the study.
Damselfish live in ocean waters throughout the world. They kill parts of coral colonies or communities, so that simple organisms like algae can grow. Damselfish use the resulting gardens of algae for feeding and producing young.
BOB DOUGHTY: In earlier times, damselfish often used staghorn corals to grow in these areas. During this period, staghorns were the most common coral in the Caribbean. The coral's long, thin branches offered the damselfish great places to hide and feed. Even after damselfish killed off parts of the staghorn colonies, the areas that remained were able to survive.
In recent years, coral diseases, storms and other activity in the environment have reduced staghorn coral populations. The corals are now listed as threatened under America's Endangered Species Act.
FAITH LAPIDUS: Les Kaufman is a biologist with Boston University and Conservation International. He says the damselfish had to find new grounds for algae after the staghorn coral disappeared. He says the damselfish are now killing off parts of slow-growing coral. This coral is not able to recover from the destruction as well as its staghorn relative. Professor Kaufman says it could take the slow-growing coral as long as one hundred years to recover.
BOB DOUGHTY: Earlier research suggested that overfishing was responsible for an increase in damselfish populations in the Caribbean. The research found that many of the bigger fish known to eat damselfish had disappeared from the area. Scientists said the increased damselfish populations led to the killing of more coral.
The new study found that the number of damselfish is not the issue. Instead, researchers are blaming the increased killing of coral on the lack of staghorn coral in the Caribbean waters.
FAITH LAPIDUS: A report in the journal Marine Policy draws attention to another threat to corals and other sea creatures. The report says international law has failed to protect coral reefs and the tropical fish that live among them from collectors.
Researchers looked at information collected for the United Nation's conservation monitoring program. The researchers say the coral trade is removing about one million five hundred thousand live stony corals from the oceans each year. They say thirty million tropical fish are disappearing every year because of a growing interest in tropical fish. Many of the fish die while being transported.
BOB DOUGHTY: Brian Tissot is a marine ecologist with Washington State University. He was one of eighteen researchers who wrote the Marine Policy paper. He says some kinds of reef fish are close to disappearing forever.
The researchers say the United States represents more than fifty percent of the trade in coral and reef fish. They have urged America to take a position of international leadership in coral reef protection and to take steps to reduce the trade's environmental effects.
FAITH LAPIDUS: Researchers in the Netherlands Antilles have discovered what they believe is the secret to how young coral find their way home. They use sound from coral reefs to guide them.
Researchers at the University of Bristol in England discovered similar movements among baby reef fish several years ago. A research team at the Carmabi Foundation in Curacao carried out experiments to see if the same was true for baby coral.
The team designed a device it called a choice chamber. Each chamber offered the coral larvae two opposing conditions. One was silence. The other was the recorded sound of a coral reef.
The researchers described what happened when they placed the coral larvae into the chamber. They said the larvae nearly always chose to follow the sound as they sought a place to call home. With this latest discovery, the researchers say noise pollution in coral environments raises yet another cause for concern for these organisms.
BOB DOUGHTY: Coral reefs exist in underwater colonies. These communities make up some of the largest living structures on earth. Some are so large that they can be seen from space.
Coral reefs were listed as plants until seventeen fifty-three. That year a French biologist who had been studying reefs in the western Atlantic discovered that they are animals. His name was J.A. de Peysonnell.
FAITH LAPIDUS: Corals are anthozoans, the largest class of organisms in the cnidaria group. Jellyfish, anemones and seafans are part of the same family. Corals are non-moving animals. They stay positioned in one place. They capture food by seizing it with their long tentacles.
Each coral polyp releases a hard calcium carbonate skeleton that serves as a base. The base grows as more calcium carbonate is released. This creates the main structure of the coral reef.
Several different species of coral can be present in the different colonies that form the reef structure. Soft corals do not form reefs, but may be present in a coral reef ecosystem.
BOB DOUGHTY: Scientists have identified thousands of different species of reef-building coral. They have also discovered hundreds of species of soft corals and deep-sea corals. Progress in science and technology is leading to the identification of even more species of coral each year.
Two years ago, scientists discovered more than one hundred corals in the Great Barrier Reef and on a reef near northwestern Australia. The scientists said that about half of the coral species were new to them.
The four-year study looked at the health, diversity and biological make-up of the reef. The scientists investigated the effect of pollution and climate change on what they called the rainforests of the ocean.
FAITH LAPIDUS: The study was part of a larger ten-year project called the Global Census of Marine Life. More than two thousand scientists from eighty nations have taken part in the project. The goal is to produce the first detailed list of sea creatures. The scientists are expected to release their findings later this year.
In a separate project, scientists identified seven new species of bamboo coral in deep waters near the Hawaiian Islands. The scientists believe that six of the species may represent a completely new kind of coral.
Some of the coral dated back about four thousand years. The scientists say deep-sea bamboo corals produce growth rings similar to those found on trees. They say this can provide important information about how ocean conditions change over time and how corals react to climate change.
BOB DOUGHTY: Coral reefs are extremely important to the earth's environment. They are home to millions of species of sea life that depend on coral reefs for their survival. This makes reefs an important source of food for millions of people around the world.
Coral reefs also protect coastlines from storms and flooding. And, they are important for the travel industry in some countries. Experts say a continuing reduction in coral reef populations will have harmful effects for people worldwide.
FAITH LAPIDUS: This SCIENCE IN THE NEWS was written and produced by June Simms. I'm Faith Lapidus.
BOB DOUGHTY: And I'm Bob Doughty. Listen again next week for more news about science in Special English on the Voice of America.