Northern Pacific Sea Star Invasion Control
话题：北太平洋海星入侵控制方法
The Northern Pacific sea star, which is native to the coasts of Japan, Korea, and China, has recently appeared thousands of kilometers away. Because this sea star now threatens to harm marine ecosystems in new and distant areas, scientists are currently investigating ways of controlling the spread of invasive Northern Pacific sea stars.
One method of reducing Northern Pacific sea star populations is by administering a poison called quicklime. Quicklime in its powdered form can be spread over large areas of the seafloor invaded by the sea stars. While quicklime destroys sea stars, it does not harm commercially important mollusks, such as oysters, scallops, and mussels, which are cultivated on the seafloor in many waters.
A second strategy is to introduce parasites that naturally control the spread of Northern Pacific sea stars in their native habitat. One major reason why Northern Pacific sea star populations are flourishing in distant waters is the absence of natural enemies, such as parasites. In their native environment, male sea stars are infected by parasites that specifically attack their reproductive system. If these parasites became established in distant waters, invasive Northern Pacific sea star populations could be significantly decreased.
A third measure involves sterilizing ballast water. Ships that have unloaded their cargo take aboard some amount of sea water as a weight and balance stabilizer. This sea water is referred to as ballast water. Sea star larvae (immature sea stars) float freely in the sea and are often taken up in ballast pumps. After taking aboard ballast water with numerous larvae in Northern Pacific waters, ships dump this water in ports thousands of kilometers away and thus contribute to the spread of these sea stars. If ships treated their ballast water with chemicals before releasing it in a different location, Northern Pacific sea stars could be prevented from spreading to new areas.
北太平洋海星原产于日本、韩国和中国海岸，最近出现在数千公里外的地区。 因为这种海星威胁到新地区的海洋生态系统，科学家正在研究控制其传播的方法。
生石灰很安全：
生石灰可以杀死海星，但不会伤害商业软体动物（牡蛎、扇贝、贻贝）。
会伤害本地生态：
虽然不伤商业软体动物，但会杀死本地海星。生石灰长期有效，本地海星迁入后也会死，破坏生态系统。
寄生虫能控制种群：
引入寄生虫，攻击雄性生殖系统，可以显著减少海星数量。
繁殖力太强：
寄生虫不能完全破坏雄性生殖系统，感染的雄性仍能让雌性受精。雌性能产2000万卵，影响有限。
处理压舱水能阻止传播：
海星幼虫通过船只压舱水传播，用化学物质处理压舱水可以防止传播。
还有其他传播途径：
幼虫会粘在小船和渔具上，压舱水不是唯一途径，处理压舱水无法完全阻止传播。
The reading passage argues that scientists can use three methods to control the spread of invasive Northern Pacific sea stars. 阅读总观点
However, the lecturer disagrees with this view. 听力立场
First, the reading states that quicklime can destroy sea stars without harming commercially important mollusks. 阅读观点1
However, the lecturer refutes this by saying that quicklime also kills native sea stars, which are critical to local ecosystems. 听力反驳
For example, the lecturer mentions that quicklime remains active on the seafloor for a long time, and when native sea stars move into areas previously occupied by invasive ones, they will also die. 具体例子
Second, the reading claims that introducing parasites that attack male sea stars' reproductive systems can significantly decrease invasive populations. 阅读观点2
In contrast, the lecturer argues that these parasites do not completely destroy the reproductive system. 听力反驳
Specifically, infected male sea stars can still fertilize female eggs, and since a single female can produce 20 million eggs, the impact would be minimal. 具体说明
Finally, the reading suggests that sterilizing ballast water can prevent sea star larvae from spreading to new areas. 阅读观点3
However, the lecturer points out that ballast water is not the only transport method. 听力反驳
According to the lecture, sea star larvae stick to small boat bottoms and fishing equipment, so invasive sea stars will likely continue spreading regardless of ballast water treatment. 根据讲座
The reading passage argues that scientists can use three methods to control the spread of invasive Northern Pacific sea stars. However, the lecturer disagrees with this view.
First, the reading states that quicklime can destroy sea stars without harming commercially important mollusks. However, the lecturer refutes this by saying that quicklime also kills native sea stars, which are critical to local ecosystems. For example, the lecturer mentions that quicklime remains active on the seafloor for a long time, and when native sea stars move into areas previously occupied by invasive ones, they will also die.
Second, the reading claims that introducing parasites that attack male sea stars' reproductive systems can significantly decrease invasive populations. In contrast, the lecturer argues that these parasites do not completely destroy the reproductive system. Specifically, infected male sea stars can still fertilize female eggs, and since a single female can produce 20 million eggs, the impact would be minimal.
Finally, the reading suggests that sterilizing ballast water can prevent sea star larvae from spreading to new areas. However, the lecturer points out that ballast water is not the only transport method. According to the lecture, sea star larvae stick to small boat bottoms and fishing equipment, so invasive sea stars will likely continue spreading regardless of ballast water treatment.