托福TPO27 Lecture1

Lecture1-Marine Biology (Coral Reefs) Narrator Listen to part of a lecture in a marine biology class. Professor So we have been fairly thorough in our discussion about coral reefs, which of course are prominent, oceanic features made of hard limestone skeletons produced by tiny coral animals. We’ve gone over where coral reefs are usually formed – along the edges of shallow ocean banks in tropical or subtropical regions, and the fact that they are declining at an alarming rate. But I don’t want to leave you with the impression that all is lost. There are several techniques being employed today that could prove useful in assuring the future of the reefs. Now, we’ve talked in depth about coral bleaching, or whitening, which as you recall, is a symptom of …well that the coral is suffering. As you know, coral is very sensitive to water temperature. Even though one or two degree Celsius rise in sea surface temperature for a relatively short amount of time can cause bleaching. Recently, researchers have used data collected by monitoring surface water temperatures to improve the ability of a reef to recover from bleaching. One future possibility is that improved monitoring can help predict where and when bleaching will occur, which might potentially enable us to mitigate its effects. And there’s another technique that’s been experimented with to try to help coral reefs recover from bleaching. It’s called coral transplantation. This involves moving young coral from a healthy reef onto a degraded reef, you know, in an attempt to regenerate the degraded reef by encouraging young healthy coral to take over. There has been some success with this, but it’s still somewhat controversial. Some scientists support it because, well for one thing, it means you don’t have to rely on the existing coral to reestablish itself because it might not be able to. But in my opinion, transplanting coral should only be used as … well as a last resort. I mean, this method is not only costly but it’s … well even if it’s successful, it still fails to address the ongoing problem, the root causes of the degradation, which really is paramount to devising an effective solution. So I don’t really take comfort in the successes they have had with transplantation. Perhaps some more constructive use of our time could be spent at researching corals that do survive, like in areas known as refugia. Refugia are areas on the reef that are seemingly, well resistant to bleaching. See, when coral reefs experience bleaching, it’s rarely a case of the whole reef being affected. There are almost always pockets of coral on the reefs that remain unaffected. And these are often the lower areas of the reef, those located in deeper water, where temperatures are lower. Now, we have evidence that corals in these locations are able to escape the destructive bleaching that affects portions of the reef in shallower or warmer water. So in my mind, it’s these refugia that are the key components of overall reef resilience. These should be the area of concentration for researchers to locate and protect those regions as a way to sustain coral reefs. And we can also protect the reefs by protecting the surrounding ecosystems, like mangrove forests and seagrass beds. Both of these grow in coastal waters, often in the vicinity of coral reefs. By protecting these areas, we also protect the coral. Let’s take, for example, the mangrove forests. Mangrove root systems have the ability to absorb and well trap sediments and pollutants in water that flows through them before they enter the ocean. This of course has beneficial results for the nearby coral reefs. And fishery’s management is another key strategy. Overfishing can be seriously disruptive to coral. Let me give you a couple of examples. Overfishing certain species of fish and shellfish like snappers, barracudas and even lobsters. Well all of these creatures feed on snails, worms and other organisms that eat coral. So depleting the number of lobsters, for example, means that we are adding to the threat of coral decline. Sea urchins are another example. They eat algae and prevent it from overwhelming the coral. Since the disappearance of sea urchins from the waters up the coast of South Florida, many coral reefs there have been smothered by the uncontrolled growth of algae.